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Leptalpheus lirai sp. nov., a new species of symbiotically living, infaunal alpheid shrimp, is described based on a single specimen from the Gulf of Santa Fe, Sucre, Venezuela. The new species belongs to an informal group of nine species within the genus Leptalpheus Williams, 1965, which is characterised by the presence of well-developed adhesive disks on the major chela. In addition, Leptalpheus axianassae Dworschak & Coelho, 1999 and Fenneralpheus chacei Felder & Manning, 1986 are recorded for the first time from Venezuela (Anzoátegui and Sucre, respectively), the latter also representing the first record of the genus Fenneralpheus Felder & Manning, 1986 for the country. These records bring to 11 the number of alpheid genera, and to four the number of species of Leptalpheus, known in Venezuelan marine waters.

The reproductive biology of the silver hatchet chela, Chela cachius, was addressed in the present study. A total of 1200 specimens were caught by fine-meshed seine nets from a large perennial water body in Bangladesh Agricultural University Campus, Mymensingh. The gonadosomatic index and the histological examination suggested that the spawning seasons of C. cachius were from February to May and from July to September. Based on histological examination, nine stages of oocyte development were determined; namely, early perinucleolus, late perinucleolus, yolk vesicle, primary yolk, secondary yolk, tertiary yolk, migratory nucleus, premature and mature stage. The absence of postovulatory follicles and hydrated eggs and the presence of two modes of eggs in the mature ovaries indicated that C. cachius was a single spawner, and its spawning frequency or strategy was a synchronous type. The average fecundity was 1708±838.86 having a standard length of 49±2.89 mm in the first season (February to May) and 1997.33±889.92, whereas the standard length was 46.66±1.53 mm in the second season (from July to September). The findings of the present study might be helpful for induced breeding of the species for commercial purposes as well as for management of the natural population (banning/restriction of fishing during spawning season) of C. cachius.

The chela of the hermit crab protects its body against the attack from predators. Yet, a deep understanding of this mechanical defense is still lacking. Here, we investigate the chela of hermit crab, Coenobita brevimanus, and establish the relationships between the microstructures, chemical compositions and mechanical properties to gain insights into its biomechanical functions. We find that the chela is a multi-layered shell composed of five different layers with distinct features of the microstructures and chemical compositions, conferring different mechanical properties. Especially, an increase of the calcium carbonate content towards the layer furthest from the exterior, unlike the chemical gradients of many crustacean exoskeletons, provides a strong resistance to deformation. Nanoindentation measurements reveal that the overall gradient of the elastic modulus and hardness in the cross-section displays a sandwich profile, i.e., a soft core clamped by two stiff surface layers. Further mechanics modeling demonstrates that the high curvature and stiff innermost sublayer enhance the structural rigidity of the chela. In conjunction with the experimental observations, dynamic finite element analysis maps the time-spatial distribution of principal stress and indicates that fiber bridging might be the major mechanism against crack propagation at microscale. The lessons gained from the study of this multiphase biological composite could provide important insights into the design and fabrication of bioinspired materials for structural applications. STATEMENT OF SIGNIFICANCE: Multiple hierarchical structures have been discovered in a variety of exoskeletons. They are naturally designed to maintain the structural integrity and act as a protective layer for the animals. However, each kind of the hierarchical structures has its unique topology, chemical gradients as well as mechanical properties. We find that the chela is multi-layered shell composed of five different layers with distinct features of the microstructures and chemical compositions, conferring different mechanical properties. Especially, a large amount of helicoidal organic fibrils form highly organized 3D woven matrix in the innermost layer, providing a strong mechanical resistance to avoid catastrophic failure. The overall gradient of the elastic modulus and hardness in the cross-section display a sandwich profile, effectively minimizing the stress concentration and deformation. The lessons gained from the multiscale design strategy of the chela provide important insights into the design and fabrication of bioinspired materials.

The main objective of the present study is to make a survey on scorpion species inhabiting New Valley governorate, Egypt as well as to make some morphometric measurements on the recorded species and to design a key for the recorded species. To achieve the aims of the study, random samples were collected during the period from April to July, 2017 and from July to September, 2019. The study revealed the presence of four scorpion species belonging to family Buthidae namely: Leiurus quinquestriatus, Androctonus amoreuxi, Orthochirus innesi and Buthacusleptochelys. The study provides a key for the identification of the species and some morphometric measurements. The morphometric measurements included: Carapace length, Mesosoma length, Metasoma length, Telson length, Aculeus length, Vesicle length, Pedipalp femur length, Pedipalp patella length, Pedipalp chela length and total body length. The study revealed significant differences between the recorded four species. It also revealed significant differences between males and females of each species.

The sexual selection over traits that favor access to mating partners could promote the emergence of sexual dimorphism when the pressure is different between sexes. Monogamous species are considered to have a low degree of sexual dimorphism. The highly diverse snapping shrimps are usually regarded as monogamous, but the mating system has been studied only in few species. We aimed to provide insights into the mating system and sexual dimorphism of Alpheus colombiensisWicksten, 1988. The adult sex ratio was female biased, and solitary ovigerous females were found, suggesting a temporary mate guarding type of mating system. Our results also revealed sexual dimorphism on the snapping claw, which is larger in males than in females. The male’s snapping claw is probably under sexual selection, which can be mediated by male-male competition or female choice. We also estimated the A. colombiensis female size at maturity at 5.2 ± 0.76 mm. Our results contradict the common idea that snapping shrimps are monogamous species, and support that A. colombiensis probably have a temporary mate guarding (e.g., males can sexually interact with more than one female, in opposition to sexual monogamy). This study also sustains the growing evidence that alpheid shrimps display snapping claw sexual dimorphism.

The invasive crab Charybdis longicollis was first reported in Mersin Bay (Mediterranean Sea/Turkey) in 1954, and since the early 1990s, its populations have been heavily parasitised by the alien rhizocephalan Heterosaccus dollfusi. In Antalya Bay, 46.6% of the trawled catch is constituted by C. longicollis. Monthly biomass values fluctuated between 67 kg km−2 (June) and 704 kg km−2 (October), with a mean of 260 kg km−2. The percentage of change in females ranged from 29% in October to 53% in January. The mean carapace width of uninfected crabs was significantly larger in males (35.1 mm) than females (30.6 mm). Male crabs (34.3%) were more heavily parasitised than females (12.1%). The reduction in size of the chela and broadening of the abdomen are two characteristic modifications of infected males. The size at first maturity was estimated at CW = 24.7 mm. Ovigerous females were found all year-round but were more abundant in spring. Male and female individuals of C. longicollis displayed a maximum of three and one modal groups per year, respectively. Natural mortality (M) was estimated as 1.1 year−1 for male crabs.

A new species from Zimbabwe, Anteon chirindense sp. nov. (Hymenoptera: Dryinidae: Anteoninae), is described and illustrated. Its relationship with other Afrotropical species of Anteon is discussed. The new species is close to A. haladai Olmi, described from Zambia, but its chela is different with inner margin of protarsomere 5 curved, whereas it is almost rectilinear in A. haladai. The key to the Afrotropical species of Anteon is modified to include the new species.

One of the most notable evolutionary innovations of marine invertebrates is the snapping claw of alpheid shrimps (Alpheidae), capable of generating a powerful water jet and a shock wave, used for defense, aggression, excavation, and communication. Evolutionary analysis of this character complex requires the study of a suite of complementary traits to discern pre-adaptations or post-adaptations of snapping behavior. A comprehensive phylogenetic analysis of the Alpheidae based on two mitochondrial and four nuclear markers, covering 107 species from 38 genera (77.6% generic coverage), is presented. Ancestral state reconstruction analyses revealed five independent origins of snapping, two of which relate to the morphologically similar but phylogenetically distant genera Alpheus and Synalpheus, highlighting significant convergence. The evolution of the five complementary traits (adhesive plaques, tooth-cavity system, dactylar joint type, chela size enlargement, and orbital hood) did not always show a significant correlation with the evolution of snapping overall, sometimes only in a few lineages, suggesting different evolutionary pathways were involved and demonstrating the versatility in the evolution of the snapping mechanisms.

The paired claws in Gazami crabs, Portunus trituberculatus, are bilaterally asymmetrical, and asymmetry is remarkable on the distal two segments of the first pereiopod, that is, the dactylus and propodus. Shells are exclusively cracked by use of the right chela, representing handedness. In Gazami crabs, handedness is reversed after autotomy of the right chela. Our study focused on the ontogeny of handedness and the mechanism of handedness reversal. Morphologically, asymmetry was first detected in megalopa larvae where the right propodus was significantly larger than the left, as was the canine at the base of the right dactylus. Presumably, the rate of chelagenesis differed between the left and right chelae. With these morphological features, the right chela functioned as a crusher. The crusher exerted a closing force two to three times that of the cutter. With loss of the right crusher, the left chela was bigger than the regenerated right chela and was converted to the crusher. In contrast, the performance of the regenerated right chela deteriorated compared to that of the original right crusher, and exertion of full closing force was inhibited by the more active left chela. Furthermore, crabs with two crusher chelae did not clearly show handedness. A decrease in size and performance of the regenerated right chela can be explained by a default program hypothesis. In conclusion, a difference in the chelagenesis rate results in bilateral asymmetry of the two chelipeds, and then handedness is generated by neural regulation in the thoracic ganglion innervating these claws. Since handedness is reversed after autotomy, the thoracic ganglion would not be lateralized in Gazami crabs. A default program hypothesis is proposed to explain the ontogeny of bilateral chela asymmetry and handedness reversal.

Since scorpions exist almost all over the world, some expected body differences exist among the species: undoubtedly, the most evident is the shape and size of their pincers or chelae. The scorpion chela is a multifunctional body component (e.g. attack/defense, mating and protection from the environment) that leads to the development of different stresses in the cuticle. How such stresses in the cuticle are accommodated by different chelae shape and size is largely unknown. Here we provide new comparative data on the hierarchical structure and mechanical properties of the chela cuticle in two scorpion species: Scorpio Maurus Palmatus (SP) that has a large chela and Buthus Occitanus Israelis (BO), with a slender chela. We found that the SP exocuticle is composed of four different sublayers whereas the BO exocuticle displays only two sublayers. These structures are different from the exocuticle morphologies in crustaceans, where the Bouligand morphology is present throughout the entire layer. Moreover, the scorpion chela cuticle presents an exclusive structural layer made of unidirectional fibers arranged vertically towards the normal direction of the cuticle. Nanoindentation measurements were performed under dry conditions on transversal and longitudinal planes to evaluate the stiffness and hardness of the different chela cuticle layers in both scorpions. The chela cuticle structure is a key factor towards the decision of the scorpion whether to choose to sting or use the chela for other mechanical functions. Statement of Significance Many arthropods such as lobsters, crabs, stomatopods, isopods, and spiders have been the subject of research in recent years, and their hierarchical structure and mechanical properties extensively investigated. Yet, except for a limited number of pre-1980 publications, comparatively little work has been devoted to the terrestrial scorpion. The scorpion chela is a multifunctional part of the body (e.g. attack/defense, mating and protection from the environment) that involves the development of various stresses in the cuticle. How these stresses in the chela cuticle are managed by different chelae shape and size is still unknown. The lack of a single study that integrates morphological characterization of the entire hierarchical structure of the scorpion chela cuticle, and local mechanical properties, significantly affects the scientific knowledge regarding important structural approaches that can be used by nature to maximize functionality.

Two isolated clades of the lined shore crab, Pachygrapsus crassipes, live on opposite sides of the northern Pacific, presenting an interesting opportunity for studies of range limits and divergence. Prior to this study, P. crassipes’ Asian range was unclear; we confirmed that it is found throughout the main Japanese Archipelago, though sporadic or absent from the Ryukyu Archipelago. We examined phenotypic variation of this species’ chelae, which are conspicuously colored and larger in males, and found positive allometry for both sexes, which was stronger in males, a common feature of sexually selected ornaments and weapons. We also found that Asian and North American clades differ significantly in chela reflectance — in contrast to previous studies, which stated that these clades were phenotypically identical. We conclude that these clades are diverging phenotypically, but that these differences are not yet sufficient to warrant distinction as separate species.

A new species of the genus Alpheus Fabricius, 1798, A. mannarensis sp. nov. is described and represented based on the materials collected from the shallow and rocky reefs, Gulf of Mannar (Thoothukudi waters), Southern India. This is the first report of Alpheus species from the Gulf of Mannar region. The new species is assigned to the Alpheus brevirostris group, and is distinguished from other species of this group by the combination of the following features: rostral ridge lower than orbital hood in lateral view and postrostral carina not extended to the middle of the carapace, palm of major chela with a transverse groove near the base of dactylus, the ultimate segment of the third maxilliped slender, fingers of minor chela of male slightly longer than palm, the first carpal segment of second pereiopods shorter than second segment, merus of third pereiopods slender and unarmed, dactylus of third pereiopods slender and subspatulate, and unique colour patterns of longitudinal light lines on the reddish body.

A new species of portunid crab from the genus Cycloachelous Ward, 1942 is described from Vietnamese waters. Cycloachelous levigatus sp. nov. is morphologically most similar to C. orbitosinus (Rathbun, 1911), which was originally described from the syntype series collected from Western Pacific area (Cargados Carajos Islands, Amirante Islands, Seychelles) and C. octodentatus (Gordon, 1938) described from one single male from Singapore. There are differences in the sternal segments, third maxilliped, chela, abdomen and male gonopode shapes. The specific status of C. levigatus sp. nov. is also clearly supported by molecular data. Aside from a comparison of this new species with other known congeners, new photographs of syntypes of C. orbitosinus and the holotype of C. octodentatus are also provided.

A new species of semi-terrestrial crab of the genus Geosesarma (Sesarmidae) is described from a limestone cave in central Sarawak, Malaysian Borneo. Geosesarma sodalissp. nov. is characterised by its quadrate carapace, absence of a flagellum on the exopod of the third maxilliped, presence of 10 or 11 sharp tubercles on the dactylus of the chela and a diagnostic male first gonopod structure. This is the sixth species of Geosesarma reported from Sarawak, and the first member of the genus collected from inside caves.

A small wild prawn of the genus Macrobrachium, found in Chiang Rai Province, Northern Thailand has some morphological features resembling four other closely related species, M. lanchesteri, M. peguense, M. kunjuramani, and M. chainatense. However, it is distinguishable from the above species in terms of distinctive golden colored antennules; number of teeth on the rostrum; number of teeth on the cutting edges of the second pereiopod; and length of carpus relative to that of chela on the second pereiopod. Moreover, DNA analysis places it far apart on the phylogenetic tree from the related species in the genus.

A new pagurid hermit crab species is assigned to the genus Kumepagurus Komai & Osawa, 2012, previously represented only by the type species, K. cavernicolus Komai & Osawa, 2012, known only from a marine cave on Ryukyu Islands, northwestern Pacific. The assignment is made because of the lack of an accessory tooth on the maxilliped 3 ischium, the operculiform right chela, the presence of two distal corneous claws on the left chela fixed finger, the simple pereopods 4 and the development and structure of the male sexual tubes on both coxae of pereopods 5, all characteristic to the type species of the genus. However, in contrast to K. cavernicolus, K. kaikata n. sp. lacks pleurobranchs on the thoracomeres 5 and 6, and in this regard, Kumepagurus is unusual in the family Paguridae. The generic diagnosis of Kumepagurus is emended to accommodate the new species, which is readily distinguished from K. cavernicolus by the proportionately shorter antennular and antennal peduncles and the right cheliped structure and ornamentation, in addition to the difference in the gill number.

A new species of the pagurid hermit crab genus Turleania McLaughlin, 1997, T. rubriguttatus, is described on the basis of two specimens, including one male and one female, from shallow subtidal waters in Kochi Prefecture, Japan. The new species appears close to T. albatrossae (McLaughlin & Haig, 1996), known from the Philippines, but the proximally unarmed dorsal surface of the right chela palm and the lack of a dorsomesial row of spines on the left cheliped carpus easily distinguish T. rubriguttatus n. sp. from T. albatrossae. Examination of the type material of T. similis Komai, 1999 and T. spinimanus Komai, 1999, and supplemental material from Japan, confirms that the two taxa are synonymous with T. senticosa (McLaughlin & Haig, 1996), as was suggested by previous authors. Re-examination clarified that in T. senticosa the maxilliped 3 has no developed arthrobranchs, and this led the author to assess the status of T. sinensis Han, Sha & An, 2016, which is also synonymised with T. senticosa.

A new species of the alpheid shrimp genus Automate de Man, 1888, A. awaji, is described on the basis of an ovigerous female holotype and three paratype specimens (sex not determined) from Awaji Island, Hyogo Prefecture, Japan. The specimens were collected from soft sediments on a shallow subtidal flat (depth 4–8 m) using an airlift suction sampler. The new species is referred to the A. evermanni Rathbun, 1901 species group, in which seven species are currently included, from various parts of the world. Automate awaji n. sp. is characterized by the combination of the following characters: eye with cornea relatively small, in lateral and subdistal position on eyestalk; antennal scaphocerite with distolateral spine not exceeding rounded distal blade; ultimate article of maxilliped 3 with longitudinal row of setae on dorsolateral surface; cheliped ischia without spiniform setae on dorsal and ventral margins; major chela of type I smooth, not rugose or tuberculate on dorsal and ventral margins, fingers not gaping; carpus of pereopod 2 with proximal-most article less than half-length of second article; propodus of pereopod 5 with grooming apparatus consisting of closely spaced transverse rows of stiff setae. It is the fourth representative of the genus Automate reported from Japan. A brief overview on Japanese species of Automate is also given.

Male skip-molting, defined for this study as when adolescent male snow or Tanner crab (Chionoecetes opilio and C. bairdi) do not molt during the winter/spring molting season, reduces the abundances of large mature males by requiring skip-molters survive at least one additional year of natural mortality before molting resumes and by increasing terminal molting at smaller sizes. These dynamics have obvious consequences for fisheries that only target and retain large mature males. Though considered common in Atlantic Canada (AC) snow crab and recently documented in Sea of Japan snow crab, skip-molting remains unexamined for Eastern Bering Sea snow and Tanner crab populations. Using chela height and shell condition data collected from 1989 to 2017, size-specific proportions of skip-molting were estimated for each species. Estimated size-specific proportions for snow crab resemble those reported for AC snow crab populations; estimated Tanner crab proportions are about twice that for snow crab when accounting for size differences between the species. Population simulations indicate skip-molting can reduce the biomass of large mature males by 12–47% relative to a population with no skip-molting, depending on species and assumptions of skip-molter survival. Regression models developed to identify important covariates of skip-molting explained only modest variation in the data (i.e., low deviance explained). Additional histological and physiological data are needed to validate classification of skip-molters from field measurements. Skip-molting proportions may have been underestimated due to shell condition misclassification of skip-molters. The stock assessments for EBS snow and Tanner crab do not consider skip-molting and assume all adolescent males molt annually. The effects of misspecified growth dynamics on assessment estimates warrant further research.

Among the Caridea Infraorder, the palaemonid shrimp from the genus Typton Costa, 1844 are commonly found in association with sponges, frequently feeding on the tissues of their hosts ((Ďuriš et al. 2011; Almeida et al. 2014; Pachelle et al. 2015; Soledade et al. 2017). Typton is mostly characterized by morphological features related to their sponge-dwelling lifestyle, as a simple and compressed rostrum, carapace smooth and antennal spines present, antennae extremely reduced and scaphocerite rudimentary. Mandible without palp, incisor process normal, reduced or absent. Second legs unequal, asymmetrical, without molar process on major chela (Bruce, 1972)

Three new species of snapping shrimps of the genusAlpheusare described from the Persian Gulf. These belong to theAlpheus edwardsiispecies-group, which is mainly characterized by unarmed orbital hoods and the presence of dorsal and ventral notches on the palm of the major chela.Alphus ankerisp. nov. shows a close affinity toA. pacificusDana, 1852 andA. heronicusBanner & Banner, 1982 bearing no balaeniceps crests in both sexes on the dactylus of the minor chela, and the merus of the major chela of both sexes are unarmed. This species differs from the closely related species by the absence of an overhanging proximal shoulder in the major chela. The other rock crevice inhabiting species,A. mohammadpourisp. nov. is diagnosed by exhibiting sexual dimorphism in its balaeniceps crests and the armed merus of the major chela. These two characters are similar to those recorded for three sandy/rubble dwelling species:A. inopinatusHolthuis & Gottlieb, 1958,A. lobidensDe Haan, 1849 andA. australiensisBanner & Banner, 1982. This new species is distinguishable from these latter species by the shape of the minor chela and colour pattern. A coral inhabiting speciesA. abumusasp. nov. appears to be closely related toA. maindroniCoutière, 1898, showing an armed merus of the major chela and the absence of spine-like seta on the ischia of the third legs. This last new species is easily discriminated fromA. maindroniby longer antennular segments, a markedly concave frontal margin between the rostrum and orbital hood, and a different colour pattern.

The Chinese mitten crab Eriocheir sinensis is an invasive species outside native range and represents a substantial threat to recipient ecosystems. It is regarded as an invasive species in Japan and has recently been found in Tokyo Bay, but little is known about its possible impacts on native species, especially on the congener Japanese mitten crab Eriocheir japonica. This study examined shelter competition between E. sinensis and E. japonica under laboratory conditions. Shelter competition trials were conducted in pairs of native and invasive males in different size combinations. Our results indicated that competition between two species was size-dependent: E. japonica always successfully defended shelter when competing with size-matched or slightly larger E. sinensis; E. sinensis always won shelter when its carapace or chela were at least 10 or 7% larger, respectively, than those of E. japonica. The two species exhibited different behavioural patterns: compared with E. sinensis, E. japonica frequently displayed positive behaviour (approach, walking leg contact, chela contact) and seldomly displayed negative behaviour (retreat). Our results highlight the important role of strong native competitors in controlling invasion success and suggest E. sinensis may be unlikely to exclude native E. japonica from its habitat by direct competition for shelter.

The isozyme variability and morphometric analysis were examined in three populations of the fiddler crab, Austruca sindensis. The crab samples were collected from the three populations of A. sindensis (Sandspit, Sonari, and Sonmiani) along the coast of Pakistan. Three different enzymes, Catalase (CAT), Carbonate dehydratase (CD), Amylase (Amy) and a general protein pattern were investigated. Two isozymes were identified to be useful for the populations differentiation of A. sindensis along the coast of Pakistan. POPGENE software was used for the analysis of banding pattern, polymorphic loci, allelic frequency, heterozygosity and genetic distance of three populations of A. sindensis; while, Minitab and MS-Excel was used for the analysis of morphometric analysis. Four polymorphic loci, CAT-I, CAT-II, CD-I and CD-II were interpretable in muscle with Polyacrylamide Gel Electrophoresis (PAGE), the allele frequency differs significantly, detected in population of the Sonmiani Bay as compared with Sonari and Sandspit. The morphometric analysis showed low level of variability among the three studied populations when total 8 selected morphometric traits were analyzed (wet weight (WW), carapace length (CL), carapace width (CW), abdominal length (AL), abdominal width (AW), enlarged chela length (EL), enlarged chela width (EW), pleopode length (PL)). Multiple statistical approaches applied; regression analysis, ANOVA and Discriminant function analysis (DFA). Among all the statistical analysis used total three traits, showed significant variations among three populations (CW, EL and AL). The result of this study indicated that not only the morphological difference reflects the environmental conditions of habitat, but also the biochemical variations can be considered as the indicator of specific population dispersal.

Duplex trichobothria (dx) are paired trichobothria situated near the tip of the fixed finger of the chela in pseudoscorpions of the Devonian plesion Dracochelidae and the extant superfamilies Chthonioidea and Feaelloidea. The paired condition, which is unique within Arthropoda, is here interpreted as the result of a coupling of two previously separate trichobothria: x1 (protonymphal) and x2 (deutonymphal). Trichobothrium et of Chthonioidea and Feaelloidea, which has previously been confused with x1 in the protonymph, does not appear until the deutonymph. In all other extant pseudoscorpions (Iocheirata), the duplex trichobothria are lacking and et appears in the protonymph. These differences allow the definition of two fundamental trichobothriotaxies: Type C (dx present, et deutonymphal) and Type D (dx absent, et protonymphal). The homologies of the trichobothria are determined by the application of Grandjean’s priority rule, which implies an orderly sequence in the addition or loss of organs within a homeotypic set, based on the postulate of trichobothrial equivalence, which states that each trichobothrium of Type D has its homologue in a trichobothrium of Type C. It is argued that trichobothriotaxy D has been derived from C through the loss of dx and an ontogenetic advance in the appearance of et, from the deutonymph to the protonymph. Thus, the absence of the duplex in Iocheirata is considered to be the result of a secondary loss. Because dx appears early in ontogeny, this loss would appear to violate the priority rule, but it is suggested that the modifications of the duplex trichobothria may have altered their nature sufficiently to make them vulnerable to suppression—a mechanism here termed metanomic release. Discrepancies between the positions of the duplex trichobothria and neighbouring organs in the protonymph and deutonymph are explained in terms of phaneric interference, whereby the appearance of a new phanere causes displacement of existing organs. Based on their morphology, the coupled trichobothria are suggested to be highly directional sensors that probably play a role during the final phase of prey capture.

The red crab Chaceon notialis is endemic to the Southwestern Atlantic (Brazil, Uruguay and Argentina), occurring from 200 to 1600 m deep. The species belongs to the Geryonidae family and exhibits a K-strategist life cycle. Due to its increased exploitation over recent decades, this marine resource requires attention regarding its conservation and management. In this work, were analyzed red crab populations from the three countries that cover the species' entire distribution range, assessing diversity and differentiation through morphometric and genetic analyses. The evaluated morphometric measurements were length and width of the carapace; length, width and height of the chelae propodus; and female abdomen width. For genetic evaluation, the following mitochondrial DNA regions were used: the partial 12S gene and the entire Control Region (861 bp); and the partial Cytochrome c oxidase subunit I (1252 bp). The morphometric results showed two distinct phenotypic groups (one from Brazil/Uruguay and the other from Argentina), with significant differences in female abdomen width and chela size. Genetic analyses, however, revealed only a single panmictic population, with no genetic structuring among the analyzed stocks. These findings suggest that the management measures applied in each country will influence the population dynamics of the others, and that international cooperation is necessary for achieving sustainable fisheries of this valuable resource. Since commercial fishing of the red crab C. notialis is not conducted in Argentina, we propose that this area can act as a biological reserve for this species. Due to the commercial importance of this crab, knowledge of the species’ diversity is of fundamental importance for its management, conservation, and to provide baselines for future biological and ecological studies.

A sacculinid rhizocephalan parasite,Sacculina lataBoschma, 1933, was discovered in the Beibu Gulf (= Gulf of Tonkin) west of Hainan Island, China, occurring in 7.4% of 363Charybdis miles(De Haan, 1835) collected by 30 trawls in July 2017. This is the first time thatS. latahas been recorded in Beibu Gulf and in the Chinese Exclusive Economic Zones (EEZs). Of the sampled crabs from 9 stations, 8 males and 19 females were found bearing externae ofS. lataon the abdomen, a prevalence of 4.1 and 11.2% in male and female crabs, respectively. The dominant size group of infected males was larger than that of females. There was no significant relationship between water depth and infection rate of the parasite. A positive correlation was found both between volume and weight of externae, and between surface area of externae and abdomen width of the host crabs. Carapace width and wet weight of infected crabs were significantly less than those of uninfected crabs. In male crabs, the first pleopods of infected individuals were shorter than normal, but their pleons were wider. The propodus of the chela of a parasitized crab was significantly larger than that of normal crabs, both in males and females. No rhizocephalan-infected female crab was found bearing eggs.

The ability to generate large closing forces is important for many animals. Several studies have demonstrated that bite or pinching force capacity is usually related to the linear dimensions of the closing apparatus. However, relatively few studies have applied geometric morphometrics to examine the effects of size-independent shape on force production, particularly in studies of crustacean pinching force. In this study, we utilized traditional and geometric morphometric techniques to compare the pinching force of Procambarus clarkii crayfish to their chela morphology. We found that males possessed larger chelae and pinched harder than females, but that their chela shape and size were weak predictors of strength. Female pinching force was significantly affected by both chela size and shape, with shape variation along the short axis of the claw contributing most to pinching force. We discuss our results in the context of reliable signaling of strength by males and females, and the different selective forces acting on chela shape in the two sexes.

Growth and moulting of male adolescent snow crabs were investigated in a laboratory culture experiment. The moulting season of adolescents was separated into two groups of earlier and later, and they were regarded as normal and skip moulters, respectively. The existence of male snow crab skip moulters was first demonstrated in the Sea of Japan. Although the precise moulting season of the earlier moulter could not be revealed owing to the captive method, the later moulter is suspected to moult approximately 1 year after the earlier moulter. Earlier and later moulters were not different in growth of carapace width or chela height during the pubertal and terminal moult. Our moult and growth results of earlier and later moulters will be useful for predicting recruitment to legally fishable (>90 mm carapace width) or valuable (hard-shelled adult) populations of male snow crab in the Sea of Japan.

Specimens of Aegla castro Schmitt, 1942 were monthly sampled from June 2012 to May 2013 from Couro stream (23°57′15″S 51°06′00″W), located in the Upper Parana river region, southern Brazil. Population structure, morphometric and functional maturity were analyzed. Allometric growth analysis on chela dimension versus carapace length (CL) was employed to recognize juveniles and adult individuals. Two sequential groups of adult males (morphotypes I and II) were recognized according to the state of development of the pair of claws. The CL where 50% of the population of individuals are adults (CL50) was used to estimate the size at the onset of morphometric maturity. Males attain morphometric maturity at same size class of females (8.0–9.0 mm CL). Males and females are heterochelous and they often show the left chela more developed. The reproductive period was extended from June to September 2012 and April to May 2013 (six months) with record of 22 ovigerous females. The recruitment occurred in the mont...

Ocean acidification (OA) adversely affects a broad range of marine calcifying organisms. Crustaceans, however, exhibit mixed responses to OA, with growth or survival negatively affected in some species, but unaffected or positively affected in others. In crustaceans, the mineralized cuticle resists mechanical loads, provides protection from the environment, and enables mobility, but little is known about how OA or interactions between OA and temperature affect its structure or function. Here, the effects of OA on the mechanics, structure, and composition of the cuticle in two Alaska king crab species was assessed. Juvenile blue king crabs ( Paralithodes platypus ) were exposed for a year to three pH levels, 8.1 (ambient), 7.8 and 7.5. Juvenile red king crabs (Paralithodes camtschaticus) were exposed for ~ 6 months to two pH levels, 8.0 and 7.8, at three temperatures: ambient, ambient + 2 °C, and ambient + 4 °C. Cuticle microhardness (a measure of resistance to permanent or plastic mechanical deformation), thickness, ultrastructure , and elemental composition were assessed in two body regions, the carapace and the crushing chela (claw). In both species tested, OA reduced endocuticle microhardness in the chela, but not in the carapace. There was no effect of pH or temperature on total procuticle thickness of the chela or carapace in either species. Reductions in microhardness were not driven by reduced calcium content of the shell. In fact, calcium content was significantly elevated in the carapace of blue king crabs and in the chela of red king crabs exposed to lower than ambient pH at ambient temperature, suggesting that calcium content alone is not a sufficient proxy for mechanical properties. Reduced chela microhardness, indicative of more compliant material, could compromise the utility of crushing chelae in feeding and defense.

An integrative analysis of sexual maturity associated with growth was developed for the spider crab Leurocyclus tuberculosus (H. Milne Edwards and Lucas, 1842). Sexual maturity was characterized based on gonadal, morphological, morphometric, and functional sexual maturity. Progress in sexual maturation was described through 13 growth stages (instars) detected by the examination of size (carapace width) frequency distributions. Mature females displayed mature ovaries, developed vaginae, open gonopores, allometric changes in the abdomen, and ovigerous stage in the transition from instar IX to instar X. Sexually mature males presented spermatophores in the distal vasa deferentia and allometric changes in several measurements of the right chela in the transition from instar X to instar XI. However, two prepubertal phases were recognized in both sexes separated from each other by a prepubertal critical molt. Preceding the second critical molt, gonopores were sealed and vasa deferentia showed no spermatophores, and therefore neither sex was able to mate. The integrated analysis of size at maturity and size frequency distributions showed that in both sexes molt to gonadal, morphological, morphometric, and functional sexual maturity occurred in advance of the terminal molt, in contrast with patterns observed in other Majoidea. Fil: Gonzalez Pisani, Ximena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Baron, Pedro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Lopez, Laura Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina

The assessment of life history traits can help to better understand the population dynamics of the respective species. We present some life history traits of the freshwater crab Potamon ibericum (Bieberstein, 1809) from the western Alborz Mountains, Iran. Carapace size at the onset of morphometric maturity was estimated using the breakpoint of the relative growth of the chela and abdomen in males and females, respectively, by implementing piecewise linear regressions. In order to quantify variations in the estimated breakpoint, a bootstrap resampling method was applied. Allometric trajectories of chelar dimensions were also applied to juveniles and adults. Sexual size dimorphism was evaluated using the dimensions of the carapace and chelae, and patterns of the carapace shape dimorphism were investigated by implementing geometric morphometric analysis. The results showed that females reach morphometric maturity at smaller sizes than males, which could be of advantage in the fluctuating environment of their freshwater habitat in order to mate as soon as possible and increase fecundity. Positive allometric trends in the length of the major chela was observed in adults of both sexes, and the possible adaptive forces on the evolution of this pattern are discussed. Results of sexual dimorphism analyses confirmed male-biased sexual size dimorphism and functional adaptation of carapace shape in both sexes.

To highlight adaptation of an endemic species to an oceanic island environment, adult morphological characteristics and growth patterns were compared between a mitten crab endemic to the Ogasawara Islands ( Eriocheir ogasawaraensis ) and a congener from mainland Japan ( E. japonica ). Mean carapace width of E. ogasawaraensis was nearly 1.6 times larger than that of E. japonica in both sexes. A difference was detected in the carapace length versus carapace width relationship between these two species. Comparing chela propodus height versus carapace width, a sexual difference was detected similarly in both species, but males had only one growth phase in E. ogasawaraensis , whereas males of E. japonica were dimorphic due to two growth phases. The regression line obtained for male E. ogasawaraensis (chela propodus height versus carapace width) was nearly on the extending line of small-phase male E. japonica . Female E. ogasawaraensis had relatively larger chelipeds than female E. japonica . As for ambulatory legs, E. japonica males had relatively longer legs than females, but no sexual difference was detected in E. ogasawaraensis. Eriocheir ogasawaraensis had relatively shorter legs than male E. japonica but longer legs than female E. japonica . Therefore, in E. ogasawaraensis sexual dimorphism was not as differentiated as in E. japonica , and the adult male dimorphism recognized in E. japonica was absent. The large body size of E. ogasawaraensis is consistent with island gigantism that is commonly found in response to a lack of large predators on isolated islands. Evolution of dimorphism can be explained by sexual selection, and the differences between the island and mainland species are presumed to be correlated with differences in the mating behavior and/or environmental factors in their habitats.

A new palaemonid shrimp genus, Unesconia gen. nov., is established to accommodate a peculiar, small, presumably sponge-associated species, Unesconia coibensis gen. et sp. nov. The description of the new genus and species is based on several specimens found in the shallow marine waters of the Coiba Archipelago, Pacific coast of Panama. Unesconia gen. nov. does not seem to have close affinities to other eastern Pacific or western Atlantic palaemonid genera, including those harbouring sponge symbionts. On the other hand, it shares many characters with three Indo-West Pacific genera, which contain sponge-associated species, viz. Paraclimenaeus Bruce, 1988, Apopontonia Bruce, 1976 and Climeniperaeus Bruce, 1996. The most important diagnostic features of Unesconia gen. nov. are the strongly carinate, dorsally dentate rostrum, with its lateral carinae greatly expanded basally and armed with strong supraorbital teeth; the non-filtering mouthparts, with mandible lacking palp; the first pereiopod chela with excavated fingers and strongly tridentate fingertips; the asymmetrical second pereiopods (chelipeds), with the major chela bearing a double-fossa mechanism on the finger cutting edges; the ambulatory pereiopod dactylus armed with one large tooth and at least two small spinules on the ventral margin of the corpus, in addition to the terminal unguis; the lateral section of the uropodal diaeresis armed with five spiniform setae, the latter not extending to the lateral margin of the exopod; and the telson with two pairs of stout long cuspidate setae on dorsal surface and three pairs of strong, elongate spiniform setae on the posterior margin.

Despite growing evidence that crustaceans produce and detect sounds, the behavioural and biological function of these sounds is still poorly understood. Here, we describe sounds produced by the New Zealand paddle crab, Ovalipes catharus, and provide evidence of intraspecific communication using underwater sound. Acoustic and video analyses of tank-based experiments show that O. catharus produce at least three distinct sounds: the rasp, zip and bass. Notably, two of these sounds, the zip and bass, were directly correlated with post-copulatory mate-guarding and courtship behaviour and produced only by competing adult male crabs in the presence of a receptive female. Rasp sounds were produced by both sexes; the occurrence significantly increased in the presence of food, and play-back experiments of these sounds initiated a foraging-like behaviour. Responses to rasps might have evolved as a result of acoustic spying. Further, we show that both the rasp and bass sounds were produced by an alternative mechanism than stridulation of the chela ridges. This refutes widespread assumptions that Ovalipes crabs use only stridulation of ridges along their chelae to produce rasp-like sounds. Our results suggest that sound production in decapod crustaceans may be more widespread than previously presumed.

Coloration, gene-sequence data (H3, 12s, 16s), and subtle features in morphology support the description of two new species, both formerly regarded to represent accepted variants of Phimochirus holthuisi s.l. While color in life consistently separates these species from P. holthuisi s.s. and from each other, morphological distinctions are subtle and less than absolute in small specimens, being based on ventral spine counts of walking leg dactyls and relative development of the superior crest on the major chela. Molecular phylogenetic analyses clearly support the separation of sister clades, representing two new species, from P. holthuisi s.s. as well as other congeners available for analysis. Both of the new species are presently known to occur widely throughout the northern Gulf of Mexico, though one occurs more commonly in the northeastern and southeastern Gulf, and may range as far south as Suriname. The other has been taken primarily in the northwestern Gulf, and is not known from outside Gulf waters. While both of the new species appear restricted to relatively deep subtidal waters of the continental shelf, Phimochirus holthuisi s.s. is instead more commonly found in shallow nearshore tropical waters on or near coral reefs. Previous literature reports of P. holthuisi usually represent, at least in part, one or both of these two new species.

A new species of the alpheid shrimp genus Salmoneus Holthuis, 1955, probably an obligate associate of ghost shrimp burrows, is described based on material from Oman (type locality: Darsait near Muscat), Iran and the Philippines. Salmoneus durisi sp. nov. is characterised principally by both chelipeds enlarged, robust, with ventral and dorsal margins of chelae carrying long fine setae, and with minor chela fingers armed with a few large teeth on cutting edges. All specimens of Salmoneus durisi sp. nov. were collected either directly from burrows of larger decapod crustaceans with the aid of a suction pump, or by exposing burrows dug under large subtidal rocks. The Iranian specimen was found together with its presumed host, Neocallichirus calmani (Nobili, 1904). Two additional specimens from Indonesia and the Solomon Islands are tentatively assigned to S. cf. durisi sp. nov., awaiting further studies.

A new snapping shrimp, Alpheus perlas sp. nov., is described based on a single complete male specimen collected on a shallow mudflat at Casayeta Island in the Las Perlas Archipelago, Gulf of Panama. The new species belongs to the large A. edwardsii (Audouin, 1821) species group characterised essentially by the presence of two notches on the major chela palm, with the dorsal notch extending posteriorly on the mesial surface. Within the eastern Pacific members of the A. edwardsii group, A. perlas sp. nov. appears to be morphologically closest to A. latus Kim & Abele, 1988 and A. burukovskyi Anker & Pachelle, 2015. Alpheus perlas sp. nov. does not seem to be specially adapted for digging and may be inquiline of a larger burrowing host, which currently remains unknown.

The present study deals with five species of the alpheid shrimp genus Salmoneus Holthuis, 1955 from the tropical eastern Pacific. One of them is new to science and is described as Salmoneus tiburon sp. nov. The new species is presently known only from the Las Perlas Archipelago in Panama and can be distinguished from all other congeners by the dentition on the cutting edges of the major chela, with some dactylar teeth reminiscent of shark teeth. It is also one of the largest species of the genus, with the carapace length of both type specimens surpassing 8.0 mm. Salmoneus serratidigitus (Coutière, 1897), a species with an ample distribution across the Indo-Pacific, is recorded for the first time from the Pacific coast of Panama and is confirmed from Colombia. Salmoneus malagensis Anker & Lazarus, 2015, previously known only from Bahía Málaga in Colombia, is recorded from Panama’s Azuero Peninsula. The remaining two species, S. excavatus Anker, 2011 and S. alvarezi Anker & Lazarus, 2015, are recorded regionally from Las Perlas Archipelago in Panama and Playa Tarcoles in Costa Rica, both for the first time since their original descriptions. An identification key to the five currently known eastern Pacific species of Salmoneus is provided. However, several immature and/or incomplete specimens herein preliminarily reported as Salmoneus spp., as well photographic records from southern California, USA, indicate the presence of further undescribed species in the eastern Pacific.

A new species of sponge–dwelling snapping shrimp , Synalpheus amintae sp. nov. from the Parque Nacional Natural Isla Gorgona, Pacific coast of Colombia, is described. This new species pertains to the denominated Synalpheus “ Gambarelloides ” species group sensu Coutiere (1909)—previously known as “ Laevimanus ” group. It was collected in the southern part of the Island, during episodes of extreme low tides, known locally as “puja”. Synalpheus amintae sp. nov. is closely related to the only two other known species of the S. “ Gambarelloides ” species group from the eastern Pacific: Synalpheus occidentalis Coutiere, 1909, from Gulf of San Jose, Lower California, and Synalpheus mulegensis Rios, 1992, from Bahia Concepcion, Gulf of California, and can be differentiated from them by the poorly developed distal portion of pollex of the major cheliped, the armature of the distal segment of third maxilliped, and the number of acute teeth of exopodal uropod. A discriminative analysis dealing with other three species of Synalpheus from the western Atlantic, with distinctive pollex of major chela reduced, is presented. A dichotomous key was elaborated to identify the species of Synalpheus “ Gambarelloides” species group from the eastern Pacific. The number of valid species described of Synalpheus from the eastern Pacific is increased to 23.

A new species of semi-terrestrial sesarmid crab of the genus Geosesarma De Man, 1892, is described from central Taiwan. Geosesarmamirumsp. nov. is distinct in possessing a strong transverse crest on the inner surface of the male chela and a diagnostic male first gonopod which is relatively long and stout, with the distal chitinous part broad and spatuliform. Like most Geosesarma species, G.mirumsp. nov. has large eggs and direct development, contrasting with the only other species known from Taiwan, G.hednon Ng, Liu and Schubart, 2004, which has small eggs and planktotrophic larvae.

Lobithelphusa Rodriguez, 1982 is endemic to southern Mexico. Assigned to this monotypic genus is the freshwater pseudothelphusid crab, L. mexicana Rodriguez, 1982. The original description based on an old, dry, male specimen in the collections of the Natural History Museum, London, is brief and the crab was only partially figured. Lobithelphusa mexicana has subsequently never been recorded from Mexico and, consequently, the conservation status of this species is unknown. The type specimen has a complete, but detached left chela; is devoid of the left ambulatory pereiopods 1–3, with the fourth missing the carpus, propodus and dactylus; and its left first gonopod detached but retained in a glass tube kept adjacent to the crab. In spite of this damage the crab is still in remarkably good condition for a specimen registered in 1860. The purpose of this study is to apply computed tomography (CT) scanning techniques on the extant type, including its first gonopod, in order to provide detailed illustrations of the crab. These, in turn, shall be used to re-describe the species in order to help establish the current distribution status of L. mexicana in Mexico, and clarify its systematic position within the Pseudothelphusidae Ortmann, 1893.

The palaemonid shrimp genus Palaemon Weber 1795 is currently represented by 87 species worldwide, of which 36 species inhabit freshwater environments. In this study, we describe a new species of the genus, P. septemtrionalis, primarily based on material collected from rivers in Miyagi Prefecture, Tohoku District, northeastern Japan. The present new species is morphologically and genetically close to Palaemon paucidens De Haan, 1841, but it is morphologically distinguishable from the latter by the chela of the pereopod 2 being longer than the carpus (versus shorter than the carpus in P. paucidens) and the possession of a low, laminar convexity on the flexor margin of the pereopod 3 dactylus just proximal to the base of the unguis (such a laminar structure is absent in P. paucidens). Comparison of partial sequences of the mitochondrial 16S rRNA gene supports the recognition of the new species. Examination of museum collections and a BLAST search on GenBank revealed that the geographical range of the new species includes the Sea of Japan side ranging from Hokkaido to Hyogo Prefecture and the Pacific side ranging from Aomori to Miyagi Prefecture. An identification key to the 13 Japanese species of the genus is presented.

A new secretive, yet brightly colored hermit crab species of the family Paguridae, Pylopaguropsis mollymullerae sp. n., is fully described based on specimens from the reefs of Bonaire, Lesser Antilles, southern Caribbean Sea. Populations of this new species were discovered and photographed in the Bonaire National Marine Park under a large coral ledge, at a depth of 13.7 m, living in crevices known by scuba divers to serve as den to a pair of “flaming reef lobsters” Enoplometopus antillensis, or a “broad banded moray” Channomuraena vittata. This new species is only the second species of Pylopaguropsis Alcock, 1905 known from the western Atlantic, the 20th named worldwide, and belongs in the teevana group of species of the genus. It is remarkably similar, and herein considered geminate, to the tropical eastern Pacific congener, Pylopaguropsis teevana (Boone, 1932), the two being characterized and uniquely different from all other species of the genus, by the striking and deeply excavated, scoop-like ventral surface of the chela of the right cheliped. Minor differences separate this new species from Pylopaguropsis teevana in the relative length of the antennal acicles (exceeding the corneas versus not exceeding the corneas in Pylopaguropsis teevana); dorsal armature of the right chela (smooth or with scattered minute tubercles versus with numerous small tubercles in Pylopaguropsis teevana); surface shape of the lateral face of the dactyl of right pereopod 3 (evenly convex versus flattened in Pylopaguropsis teevana); and coloration (red bright red stripes versus brown stripes in Pylopaguropsis teevana). The highly visible color pattern of bright red stripes on white background typical of decapods known to have cleaning symbioses with fish, dense setation on the flagella of the antennae, and preference for a crevicular habitat, combined with brief in situ nocturnal observations, suggests the possibility that Pylopaguropsis mollymullerae sp. n. engages in “cleaner” activities or functions as a “den commensal” with moray eels. The morphology and possible meaning of the observed behavior is discussed. A tabular summary of the distribution, habitat, and published information on all species of Pylopaguropsis is presented. Supplemental photographs and a video of live Pylopaguropsis mollymullerae sp. n. are included.

The nominal genera Chelomalpheus Kim, 1998 and Cavipelta Hayashi, 1998 were treated as synonyms of Stenalpheops Miya, 1997 in the paper by Anker et al. (2001). Therefore, the type species of those genera (Chelomalpheus koreanus Kim, 1998 and Cavipelta yamashitai Hayashi, 1998, respectively) were synonymized with S. anacanthus Miya, 1997. Actually, those authors ignored that the morphological characters of the three species mentioned above show differences. For instance, all type specimens of Chelomalpheus koreanus Kim, 1998 are without a caudal appendix; the large male specimens of Cavipelta yamashitai Hayashi, 1998 have an abnormal shaped chela, which corresponds with the middle stage in a growth series of another nominal species, i.e., S. anacanthus. The opportunity to study abundant specimens from the China seas established that the type specimens of S. anacanthus Miya, 1997 are in fact composed of two species, and the same was found for the type specimens of Cavipelta yamashitai Hayashi, 1998; in addition, Chelomalpheus koreanus Kim, 1998 was found to be a valid species and is transferred to Stenalpheops; and S. crangonus (Anker, Jeng & Chan, 2001) is herein synonymized with S. anacanthus Miya, 1997, which name has priority, and this valid species is now re-described herein.

A new sponge-associated species, Paraclimenaeus michaeli sp. nov. from Sulawesi, Indonesia, and Singapore, is described and illustrated. The new species can be distinguished from its congenerics by: (1) the downwards curved rostrum with 2 acute dorsal teeth subdistally, (2) the absence of subdistal teeth on the fixed finger of the major second chela, (3) the pairs of dorsal telson spines at about 0.33 and 0.66 of the telson length, (4) the caudal fan sparsely setose, and (5) the second pereiopods without subdistal teeth on fixed finger. To evaluate its relationship with congenerics and species of the related genera Apopontonia and Climeniperaeus, a phylogenetic analysis based on the 16S mitochondrial gene is presented. A key for the identification of the species in Apopontonia, Climeniperaeus and Paraclimenaeus is proposed.

The distribution and occurrence of epibionts on the dorsal carapace, ventral carapace and chela of 325 specimens of Callinectes amnicola (De Rocheburne, 1883) (103.4 – 138.7 mm carapace width) from the Qua Iboe (QIRE) and Imo River (IRE) estuaries in southeast Nigeria was determined. The only ectosymbiont observed was cirriped barnacle, Chelonibia patula, mostly of smaller sizes (2.25 mm), infesting only 25-29% of intermoult crabs, more on females and in the Imo River estuary, with an average of four barnacles per crab, presupposing low level of epibiont-host interaction. There was no significant difference (P>0.05) in spatial distribution but epibionts were highest in the dry season in low salinity IRE (0.53‰) and in wet season in the medium-salinity QIRE (17.4‰). No public health risk has been reported among crab consumers in the study area. This study highlights epibiont-host interaction in the study area largely unknown for proper management of the fishery., Određena je distribucija i pojava epibionta na leđnoj i trbušnoj strani oklopa i kliještima kod 325 uzoraka Callinectes amnicola (De Rocheburne, 1883) (103,4 - 138,7 mm širine oklopa) s ušća rijeka Qua Iboe (QIRE) i Imo (IRE) u jugoistočnoj Nigeriji. Jedini uočeni ekosimbiont je rak vitičar, Chelonibia patula, uglavnom manjih dimenzija (2,25 mm) na samo 25-29% rakova, više kod ženki na ušću rijeke Imo, s prosjekom od četiri vitičara po raku, što ukazuje na nisku interakciju epibionta-domaćina. Nije bilo statistički značajne razlike (P > 0,05) u odnosu na prostornu rasprostranjenost, ali epibionti su bili najviši u sušnom razdoblju u IRE niske slanosti (0,53 ‰), te u vlažnoj sezoni u QIRE srednje slanosti (17,4 ‰). Nije bilo utvrđenih rizika za zdravlje među konzumentima rakova u području istraživanja. Ovo istraživanje naglašava interakciju epibionta-domaćina u području istraživanja koje je u velikoj mjeri nepoznato po pravilnom upravljanju ribarstvom.

Successful invasion by nonindigenous species is often attributed to high propagule pressure, yet some foreign species become widespread despite showing reduced genetic variation due to founder effects. The signal crayfish (Pacifastacus leniusculus) is one such example, where rapid spread across Japan in recent decades is believed to be the result of only three founding populations. To infer the history and explore the success of this remarkable crayfish invasion, we combined detailed phylogeographical and morphological analyses conducted in both the introduced and native ranges. We sequenced 16S mitochondrial DNA of signal crayfish from across the introduced range in Japan (537 samples, 20 sites) and the native range in western North America (700 samples, 50 sites). Because chela size is often related to aggressive behavior in crayfish, and hence, their invasion success, we also measured chela size of a subset of specimens in both introduced and native ranges. Genetic diversity of introduced signal crayfish populations was as high as that of the dominant phylogeographic group in the native range, suggesting high propagule pressure during invasion. More recently established crayfish populations in Japan that originated through secondary spread from one of the founding populations exhibit reduced genetic diversity relative to older populations, probably as a result of founder effects. However, these newer populations also show larger chela size, consistent with expectations of rapid adaptations or phenotypic responses during the invasion process. Introduced signal crayfish populations in Japan originate from multiple source populations from a wide geographic range in the native range of western North America. A combination of high genetic diversity, especially for older populations in the invasive range, and rapid adaptation to colonization, manifested as larger chela in recent invasions, likely contribute to invasion success of signal crayfish in Japan. © 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

We studied the ontogenetic allometry pattern in the freshwater brachyuran crab Potamon fluviatile (Herbst, 1785) to describe some new sexual dimorphic features on the ontogenic trajectories of the chelae. We surveyed carapace width, chela length and width, dactylus length, and propodus length of both chelae of 93 females and 114 males to the nearest 0.05 mm using a vernier caliper. Our main result was the identification of morphological biometry showing a variability of the chela linked to growth allometry, with some different between-sex ontogenic trajectories. Specifically, we emphasized how the morphometric features of the chelae change during body-size growth with different increasing rates. Particularly, the observed significant shape changes are mainly due to positive allometries in both sexes, although negative allometries (the latter visible only in the propodus length of females) and isometries were observed as well. Our study confirms that a form of sexual dimorphism exists in the ontogenetic allometric trajectories of P. fluviatile in both the large and small chelae, these trajectories being related to mechanical aspects in predation, food manipulation, mate acquisition, and between-sex differences in aggressiveness during antagonistic fights.

We have investigated the microstructures and mechanical properties of four crab species Paralithodes brevipes, Eriocheir japonicas, Geothelphusa dehaani, and Telmessus acutidens and analyzed the molecular and elemental data of their chela. In the visible brown region (BR) at the distal end of the dactylus tip in Paralithodes brevipes and Eriocheir japonicas, the elastic modulus and calcium (Ca) content were lower than in the white region (WR). Near the interface between BR and WR, Ca, and carbon (C) composition changed continuously. Molecular analysis shows that the dactylus tips of the chela in P. brevipes and E. japonicas were composed of chitin and calcium carbonate. In G. dehaani and T. acutidens, the Ca concentration was homogeneous in the top portion (TP) of the dactylus dentitions. The lowest value of Ca concentration was found near the surface of the bottom portion (BP) on the dactylus dentitions. In G. dehaani, the elastic modulus distribution in the TP was maximum near the outermost surface, and gradually decreased in the inner layers; the lowest elastic modulus in the BP was near the outermost surface, and the distribution increased in the inner layer. These results show that the biological composite was as a continuous structure near the interface of the dactylus tip. Understanding the microstructures of the dactyla of crabs might help the study and development of bio-inspired composites for pinching.