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Photos of predation of sagitta (Chaetognatha) to fish larvae are presented for the first time for the Black Sea. While analyzing ichthyoplankton samples obtained in May and November in 2017 (94ᵗʰ and 98ᵗʰ cruises of RV “Professor Vodyanitsky”) several sagittas were found with their guts containing fish larvae. Fish larvae seem to have been captured by sagittas in the same way as sagittas in cannibalism cases, with both folding in half at the spot of capture. The data obtained allow us to assume sagittas in conditions of high abundance of eggs and fish larvae in the plankton to be not only a food competitor of larvae and juveniles of fish, as a fodder plankton consumer, but an active predator, being able to play a significant role in the elimination of ichthyoplankton.

International audience; The recent discovery of a nuclear giant virus that infects chaetognaths (small marine invertebrates) led us to reanalyze the surprising structures previously observed in this taxon. These elements, initially thought to be bristles and, later, bacteria, have been observed in two species and are in fact viral particles that likely correspond to two host-specific species. All of these viral particles have a spindle (fusiform) shape, an outer envelope and a tegument-like structure surrounding one internal membrane delimiting a compartment containing the genome and proteins. Electron photographs have provided a view of the sequential viral assembly and egress processes, which are concomitant and occur through the cytoplasmic membrane. During viral budding, the tegument-like wall self-assembles from a ring structure. Moreover, in the cell cytoplasm, the viral nucleoid is surrounded by two membranes. The virions that infect Paraspadella gotoi have a length range of ~2.5-3.1 μm and are not completely covered by the envelope revealing a kind of small "paintbrush" that is probably protein in nature. This structure does not appear in the viral particles infecting Spadella cephaloptera, who's the size of a virus exceeds 4 μm, which is approximately twice the length of the bacterium E. coli and represents the longest known length of a virus. Moreover, they are perhaps the first known photographs of giant viruses (1967). Future genomic studies and further ultra-structural investigations are needed to improve knowledge of these viruses, which may represent a novel virus family for we provisionally propose the name Klothoviridae and the type species Klothovirus casanovai.

International audience; Chaetognaths are marine invertebrate organisms that constitute a small phylum of very abundant animals. Chaetognaths exhibit several morphological, physiological, anatomical and molecular peculiarities. In all known chaetognath mitochondrial (mt) genomes, the number of genes encoding tRNAs is always small. In addition, the primary sequences and secondary structures of chaetognath tRNAs are not conventional. Several metazoan mt-trn genes (encoding tRNAs) exhibit nucleotide triplets corresponding to stop codons (TAG/TAA) and/or start codons (ATG/ATA) at specific conserved positions. The products of genes that bear one or both types of these codons are known as ss-tRNAs (ss for stop/start). Indirect analyses strongly suggest that in chaetognath mt genomes, some of these start and stop codons could be functional. Moreover, taking these codons into account in the algorithms predicting tRNAs makes it possible to identify and correct several potential annotation errors. Furthermore, a type of ss-trn gene appears to have emerged by duplication in order Aphragmophora.

The population size structure, vertical distribution, gonad maturation, individual fecundity and embryonic development of the chaetognath Eukrohnia hamata were studied in the northernmost part of its distribution area, the Arctic Ocean. Analysis was based on stratified zooplankton samples collected in the Canada Basin during July 2005 that covered the depth range from the surface down to the bottom (or 3000 m). E. hamata abundance averaged 1087 ind. m-2 (0.8% of zooplankton community), while their biomass averaged 379 mg DW m-2 (10% of community biomass). Individual length of E. hamata ranged from 2 to 41 mm. Younger juvenile specimens 20 mm contributed only 5%. Size of the mature specimens, carrying 2 ovoid egg-sacs within a marsupium, varied between 24 and 38 mm. E. hamata was encountered down to 1000 m depth, but was absent from deeper layers. Specimens with eggs or developing embryos in the marsupium, as well as the smallest young specimens of 2–3 mm, were found predominately between 300 and 750 m depths. Juveniles 4–6 mm and 7–12 mm long showed a clear preference for the depth layer between 100-500 m and 50–500 m, respectively, suggesting an upward ontogenetic migration of the growing specimens to the strata with richer prey densities. The peak of fully mature male, female and specimens with ruptured marsupial sacs within the lowermost portion of the species vertical range (500–750 m) indicates that the ascent of growing individuals is followed by the downward migration of mature ones for reproduction. The number of eggs and embryos in marsupial egg sacs of 63 mature specimens collected on six expeditions to the deep Arctic Ocean (1993–2016) averaged to 153 with a maximum of 266 ind-1. For the first time, embryonic development of E. hamata from the egg until young hatching from marsupial sacs is documented. Our data provide novel insights into E. hamata ecology and distribution in the deep Arctic Ocean.

Zooplankton composition and abundance at two stations located in exposed (station I) and protected (station II) areas of Bakkhali sub-tropical estuary, Cox’s Bazar, Bangladesh were investigated monthly from January 2006 to December 2006. Thirty-three zooplankton taxa were identified. The major groups of zooplankton encountered were Copepoda, Chaetognatha, Mysidaceae, Luciferidae, Amphipoda, Acetes, Hydromedusae, Cladoceran, Decapod and fish larvae. The percent composition of Copepoda was the highest (79.5-84.8%) among zooplankton groups followed by Chaetognatha (5.5-6.0%) and Mysidaceae (3.3-6.8%). The abundance of zooplankton was relatively higher (87674individuals/m3) in protected (mangrove) as compared to exposed (salt marsh; 68719 individuals/m3) site during the study period. Canonical Correspondence Analysis indicated that the abundance of copepods was influenced by rainfall, water temperature and transparency in this estuarine environment, and considered coastal and estuarine dominant.Key words: Zooplankton, Mangrove, Salt marsh, Estuary and sub-tropical

The species list and taxonomic keys for the family Tokiokaispadellidae Salvini-Plaven 1986 are given. A new species, Protoheterokrohnia gen. n., is described (diagnosis): eye with dark pigment; corona ciliata located at eye level, on the neck; a greater part of the posterior fins located on the trunk section; thick rays are present in fins; no gut diverticula; papillae on the ventral part of the head form the right toruli. Drawings, data on the species distribution, and a detailed description of four new species (P. protomirabilis sp. n., P. clavata sp. n., P. bogutskayae sp. n., and P. scipioformes sp. n.) from the Laptev Sea are presented.

Sagittidae species from the Arctic Seas of Russia and adjacent water bodies are listed. Diagnoses for the subclass Sagittiones Kassatkina 2011, order Aphragmophora Tokioka 1965, and family Sagittidae Claus et Groben 1905 are given. Five new species are described in detail with differential diagnoses provided, and identification keys for the genera Sagitta, Parasagitta, and Pseudosagitta are given. The study is illustrated by drawings and photographs.

Chaetognatha is a minor phylum, comprising transparent marine invertebrates varying in size from 0.5 to 12 cm. The exact phylogenetic position of Chaetognatha in Metazoa has not been deciphered as some embryological characteristics place chaetognaths among deuterostomes and some morphological characteristics place these among protostomes. In this study, the major factors that drive synonymous codon usage bias (SCUB) in the mitogenomes of representative species of Chaetognatha and chosen species of other closely related phyla were analyzed. Spearman's rank correlation analyses of nucleotide contents suggested that mutational pressure and selection were acting in all examined mitogenomes but with varying intensities. The quantification of SCUB using effective number of codons vs. GC composition at the third codon position (GC 3 ) plot suggested that mutational pressure due to GC compositional constraints might be one of the major influencing forces driving the SCUB in all chaetognaths except Sagitta enflata. However, neutrality plots revealed no significant correlation between GC 3 and cumulative GC content at first and second codon positions (GC 12 ) in all other species, except in Daphnia pulex. The parity rule 2 bias plot showed that significant compositional differences existed between C and G, as well as between A and T, contents in most of the protein-coding genes (PCGs) and, comparatively, A and T contents were used more proportionally than C and G contents in all chosen mitogenomes. Chi-square analysis revealed the presence of putative optimal codons in all species, except in S. enflata. The correspondence analysis identified that mutational pressure and selection act on the mitogenomes of the selected chaetognaths and other phyla with varying intensities. The cluster analysis based on relative synonymous codon usage (RSCU) values revealed that RSCU variations in the PCGs of mitogenomes of chaetognaths are more comparable with those of protostomes. Apart from mutational pressure and selection, certain unknown selective forces might be acting on the PCGs in the analyzed mitogenomes as the phenomenon of SCUB could not be explained by mutational pressure, by selection, or by both.

The Red Sea has been recognized as a unique region to study the effects of ecohydrographic gradients at a basin-wide scale. Its gradient of temperature and salinity relates to the Indian Ocean monsoon and associated wind-driven transport of fertile and plankton-rich water in winter from the Gulf of Aden into the Red Sea. Subsequent evaporation and thermohaline circulation increase the salinity and decrease water temperatures toward the North. Compared with other ocean systems, however, relatively little is known about the zooplankton biodiversity of the Red Sea and how this relates to Red Sea latitudinal gradients. Among the most abundant zooplankton taxa are Chaetognatha, which play an important role as secondary consumers in most marine food webs. Since Chaetognatha are sensitive to changes in temperature and salinity, we surmised latitudinal changes in their biodiversity, community structure and diel variability along the coast of Saudi Arabia. Samples were collected at nine coral reefs spanning approximately 1500 km, from the Gulf of Aqaba in the northern Red Sea to the Farasan Archipelago in the southern Red Sea. Thirteen Chaetognatha species belonging to two families (Sagittidae and Krohnittidae) were identified. Latitudinal environmental changes and availability of prey (i.e. Copepoda, Crustacea) altered Chaetognatha density and distribution. The cosmopolitan epiplanktonic Flaccisagitta enflata (38.1%) dominated the Chaetognatha community, and its abundance gradually decreased from South to North. Notable were two mesopelagic species (Decipisagitta decipiens and Caecosagitta macrocephala) in the near-reef surface mixed layers at some sites. This was related to wind-induced upwelling of deep water into the coral reefs providing evidence of trophic oceanic subsidies. Most Sagittidae occurred in higher abundances at night, whereas Krohnittidae were more present during the day. Chaetognatha with developing (stage II) or mature ovaries (stage III) were more active at night, demonstrating stage-specific diel vertical migration as a potential predator avoidance strategy.

Although chaetognaths inhabiting polar ecosystems are relatively well known, there are few reports on their functioning in the Antarctic coastal plankton community. The presented results provide the first comprehensive description of population structure of chaetognaths in the neritic zone west of the Antarctic Peninsula. The studies were performed on samples collected in Admiralty Bay, from December 1994 to June 1995. Following six chaetognath species were determined: Eukrohnia hamata, E. bathypelagica, E. fowleri, Pseudosagitta gazellae, P. maxima and Solidosagitta marri. The representatives of Eukrohnia were observed almost throughout the research period, whereas those of Pseudosagitta and Solidosagitta were found only during first four months of our investigation. Eukrohnia hamata showed a strong dominance in respect to abundance (max. 445 ind./1000 m3). The mean abundance of all taxa significantly fluctuated in the study period and across weeks. Generally, all species were represented by the first three maturity stages (I-III), individuals stage IV occurred sporadically, and mature specimens (stage V) were not recorded at all. Morphometric analysis of the most abundant species showed distinct differences in their total length and body proportions. Our findings may suggest that chaetognath populations in Admiralty Bay are migrant, dependent on the inflow of water from the Bransfield Strait, but to prove this statement further, round year study is necessary.

Daily ration of the Okhotsk Sea herring is estimated as 3.9 % of the body weight in spring, 7.7 % in summer, 4.9 % in autumn, and 1.2 % in winter. Its mean annual consumption is assessed as 35.9 million t of prey, mainly zooplankton (97.3 % of the ration) including 15.86 · 10 6 t of euphausiids (43.0 %), 15.16 · 10 6 t of copepods (41.1 %), and 2.7 · 10 6 t of amphipods (6.2 %). In total, 6.9 % of the Euphausia stock, 3.7 % of the Copepoda stock, 9.7 % of the Amphipoda stock, and 0.1 % of the Chaetognatha stock are grazed by herring annually. The herring consumption is on average 18.9 % of the total volume of food consumed by nekton in the epipelagic layer of the Okhotsk Sea.

Chaetognath mitogenomes exhibit more than one tRNA-like sequence as previously suggested.16S rRNA genes appear as chaetognath tRNA nurseries.TRNA pairs seem templated by sense-antisense strands as previously suggested for multifunctional ribosomal-like protogenomes. The chaetognaths constitute a small and enigmatic phylum of little marine invertebrates. Both nuclear and mitochondrial genomes have numerous originalities, some phylum-specific. Until recently, their mitogenomes seemed containing only one tRNA gene (trnMet), but a recent study found in two chaetognath mitogenomes two and four tRNA genes. Moreover, apparently two conspecific mitogenomes have different tRNA gene numbers (one and two). Reanalyses by tRNAscan-SE and ARWEN softwares of the five available complete chaetognath mitogenomes suggest numerous additional tRNA genes from different types. Their total number never reaches the 22 found in most other invertebrates using that genetic code. Predicted error compensation between codon-anticodon mismatch and tRNA misacylation suggests translational activity by tRNAs predicted solely according to secondary structure for tRNAs predicted by tRNAscan-SE, not ARWEN. Numbers of predicted stop-suppressor (antitermination) tRNAs coevolve with predicted overlapping, frameshifted protein coding genes including stop codons. Sequence alignments in secondary structure prediction with non-chaetognath tRNAs suggest that the most likely functional tRNAs are in intergenic regions, as regular mt-tRNAs. Due to usually short intergenic regions, generally tRNA sequences partially overlap with flanking genes. Some tRNA pairs seem templated by sense-antisense strands. Moreover, 16S rRNA genes, but not 12S rRNAs, appear as tRNA nurseries, as previously suggested for multifunctional ribosomal-like protogenomes.

Horizontal changes in mesozooplankton abundance, biovolume and size spectra at western boundary currents in the subtropical North Pacific during winter 2012 were evaluated by ZooScan measurement on samples collected by net towing from 23 stations. Zooplankton abundance and biovolume ranged from 35.1 to 456.8 ind.m(-3) and 43 to 231.7 mm(3) m(-3), respectively. Copepoda were the most dominant species, followed by Chaetognatha and Tunicata. According to the Bray-Curtis cluster analysis based on biovolume of zooplankton size classes of each taxonomic group at intervals of 1 (log(2) mm(3) ind.(-1)) between 6 and 12 and considering the effect of regional factors, zooplankton communities were classified into four groups, which basically coincided with the geographical patterns of different currents: the North Equatorial Current (NEC), the North Equatorial Counter Current (NECC), the Kuroshio Current (NC), and the Mindanao Eddy (ME), respectively. The largest and lowest biovolumes were observed in the NECC region and the NEC region, respectively, and both were dominated by the 0.3 to 1 mm equivalent spherical diameter (ESD) size class, while the ME region was dominant by the 1 to 2 mm ESD size class. The slopes of the normalized biovolume size spectra for each group were slightly lower than -1 (range from -0.85 to -0.92), which indicates that zooplankton communities in the study area were characterized by low productivity and high energy transfer efficiency. (C) 2015 Elsevier B.V. All rights reserved.

Nowadays, the evidences relating the impacts of climate change in gelatinous zooplankton communities are recurrent, and it must be considered due to their key role in marine pelagic food webs. This study aims to investigate the latent influence of the environmental variability on interannual abundance changes of two less-talked gelatinous zooplankton groups, which were Tunicata and Chaetognatha in the Mondego estuary (Portugal), over the period 2003-2012. In this study was possible to find a correlation between environmental factors and species abundance exhibiting marked interannual variability, particularly, after drought years. In addition, higher abundances were found in the mouth and middle stations, close to the entrance of the estuary. Our results also showed several resemblances with the upshots reported in the Indian Ocean and/or in California (USA), that contributed to complement the baseline data, carrying important information about these holoplanktonic groups and the way that environmental factors affects their variability in the Mondego estuary. Hoje em dia, os estudos que relacionam os impactos das alterações climáticas com as comunidades de zooplâncton gelatinoso são recorrentes, e não devem ser ignoradas devido ao seu papel fundamental nas cadeias alimentares pelágicas dos ecossistemas marinhos. Este estudo tem como objetivo investigar a influência latente da variabilidade ambiental sobre as alterações na abundância interanual de dois grupos menos estudados de zooplâncton gelatinoso, tunicados e quetognatas, no estuário do Mondego (Portugal) durante o período de 2003-2012. Neste estudo, foi possível encontrar uma correlação entre os fatores ambientais e a abundância das espécies, mostrando uma variabilidade interanual acentuada, particularmente após os anos de seca. Os organismos apresentaram maior abundância nas estações da embocadura e intermédias, perto da entrada do estuário. Os nossos resultados também mostraram várias semelhanças com os resultados relatados no Oceano Índico e/ou na Califórnia (EUA), contribuindo assim para complementar os dados já existentes, trazendo informações importantes sobre estes grupos holoplanctónicos e como os fatores ambientais afetam a sua variabilidade no estuário do Mondego. Mestrado em Biologia Marinha

Although Serratosagitta tasmanica is widely distributed, there is little information on how hydrology affects its distribution, abundance and demography. In this study we analyzed the distribution, carbon content and population structure of S. tasmanica in the Southwestern Atlantic Ocean. Samples were collected at 34°–39°S (Northern Argentine Continental Shelf in winters of 1999 and 2000) and at 47°–55°S (Southern Argentine Continental Shelf in spring 2005, summer 2006 and winter 2006). The analysis of more than 8500 individuals showed that its dominance decreased spatially from south to north, whereas biomass (mgC/m 2 ) increased temporally by three orders of magnitude between spring (4.06) and summer (12.7). In the southern area the presence of all maturity stages in all seasons suggests year-round reproduction, with maximum reproductive activity in winter. Body length increased with increasing latitude and decreased with temperature. We detected differences in the morphology of seminal vesicles and ovary length between mature specimens. In the northern area all individuals exhibited short-type ovaries whereas in the southern area individuals had either short or long ovaries, suggesting that some individuals of the latter area had been advected from the Southern Pacific Ocean through the water discharged from the Magellan Strait. Fil: Sotelo, Inés. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina Fil: Thompson, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Unidad Ejecutora de Investigaciones en Producción Animal. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Unidad Ejecutora de Investigaciones en Producción Animal; Argentina Fil: Sabatini, Marina Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina Fil: Reta, Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina Fil: Daponte, María Cristina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina

International audience; The chaetognaths live in various marine habitats, mostly in plankton. Some species are provided with glandular canals, described herein; they are true coelomoducts. Their nature was already suspected but, curiously, this information was overlooked. Knowledge of this fact would have prevented numerous incorrect positioning of the phylum in the tree of life.

The literature on gelatinous (Cnidaria, Ctenophora, Tunicata) and semi-gelatinous (Chaetognatha) zooplankton from 32 Brazilian estuaries is reviewed. Altogether 104 species have been recorded, 70 cnidarians, 2 ctenophores, 14 chaetognaths, 13 appendicularians and 5 thaliaceans. All groups are understudied with only few detailed data available. Most of these gelatinous and semi-gelatinous taxa are typically oceanic, and thus the low diversity in estuarine systems was expected and is not probable to increase much with increasing sampling effort. Contrary, the meroplanktonic hydromedusae from the orders Anthoathecata and Leptothecata are diversified in estuarine ecosystems and the respectively 29 and 19 species currently reported from Brazilian estuaries are an underestimation and certainly will increase considerably with increased sampling effort. The best-studied taxa are the chaetognaths, followed by appendicularians, and very little is known about the other taxa, particularly concerning ctenophores and thaliaceans. We summarize the main tendencies of each taxon regarding diversity, abundance, temporal and spatial variations, species composition, and the most abundant species. In addition, we also provide general guidelines for future research on gelatinous and semi-gelatinous zooplankton taxa from Brazilian estuaries.

Near-bottom zooplankton communities have rarely been studied despite numerous reports of high zooplankton concentrations, probably due to methodological constraints. In Kongsfjorden, Svalbard, the near-bottom layer was studied for the first time by combining daytime deployments of a remotely operated vehicle (ROV), the optical zooplankton sensor moored on-sight key species investigation (MOKI), and Tucker trawl sampling. ROV data from the fjord entrance and the inner fjord showed high near-bottom abundances of euphausiids with a mean concentration of 17.3 ± 3.5 n × 100 m−3. With the MOKI system, we observed varying numbers of euphausiids, amphipods, chaetognaths, and copepods on the seafloor at six stations. Light-induced zooplankton swarms reached densities in the order of 90,000 (euphausiids), 120,000 (amphipods), and 470,000 ind m−3 (chaetognaths), whereas older copepodids of Calanus hyperboreus and C. glacialis did not respond to light. They were abundant at the seafloor and 5 and 15 m above and showed maximum abundance of 65,000 ind m−3. Tucker trawl data provided an overview of the seasonal vertical distribution of euphausiids. The most abundant species Thysanoessa inermis reached near-bottom concentrations of 270 ind m−3. Regional distribution was neither related to depth nor to location in the fjord. The taxa observed were all part of the pelagic community. Our observations suggest the presence of near-bottom macrozooplankton also in other regions and challenge the current view of bentho–pelagic coupling. Neglecting this community may cause severe underestimates of the stock of pelagic zooplankton, especially predatory species, which link secondary production with higher trophic levels.

The phylum Chaetognatha (arrow worms) comprises a group of small marine predators that constitute a critical component of the zooplankton community throughout the world's oceans. Various phylogenetic affiliations have been proposed for the Chaetognatha, for which there are at least nine possible phylogenetic positions. Resolving the phylogenetic position of the chaetognaths is a key in understanding the fundamental developmental features of bilaterians. In comparison with the typical gene content of metazoan mitogenomes, two protein-coding genes (atp6 and atp8) are absent from all chaetognaths. The two mitogenomes sequenced from Sagitta crassa and Zonosagitta nagae in this study nevertheless contain two and four tRNA genes, respectively, in contrast to those of the other five chaetognaths reported where only one tRNA gene (trnMet) is present, thus invalidating the view that all chaetognath mitogenomes have a single tRNA gene. A conserved major gene order shared by all chaetognaths could be partially identified in many protostome mitogenomes, but not in any ancestral mitogenome gene arrangement of the four deuterostome groups. Phylogenetic analysis of the deduced amino acid sequences of protein-coding genes from 85 mitogenomes of 19 groups suggests the Chaetognatha to be a sister group to the protostomes, a result consistent with evidences from the developmental pattern and other molecular analyses.

Change in prey for pacific salmons in the eastern Bering Sea is considered between the periods of relatively warm (2003-2006) and relatively cold (2007-2012) conditions on the base of data obtained in the frames of BASIS research program. In the warm period, mean biomass of the large-sized, medium-sized and small-sized fractions of zooplankton was 287.9, 258.2, and 109.2 mg/m 3 , respectively. In these conditions, fish prey was the basis of diet for pink salmon (70-68 % of ration), chum salmon (64-84 %) and sockeye salmon (45-87 %). Pink, chum, sockeye, and coho salmons had similar diet with the dominance of juvenile walleye pollock (similarity 70-90 %), in contrast to the diet of chinook salmon (40-70 % similarity with others). In the cold period, the large-sized zooplankton was much more abundant (1094.8 mg/m 3 on average) mostly due to higher abundance of Copepoda and Chaetognatha; euphausiids, hyperiids, and pteropods were more abundant, as well. In these conditions, zooplankton, mainly euphausiids Thysanoessa raschii and hyperiids Themisto libellula and T. pacifica , dominated in the diet of plankton-eating salmons: 86-92 % of the ration for pink salmon, 88-92 % for chum salmon, and 74-81 % for sockeye salmon; all these species and chinook juveniles had similar diet (70-80 % similarity). On the contrary, predatory salmons as coho and chinook adults still preyed on fish. Mean daily rations in the warm/cold periods are estimated as 12.1/9.4 % of body weight for sockeye salmon with the length 10-20 cm, 8.6/7.3 % for sockeye salmon 20-30 cm, 8.3/13.8 % for chum salmon 10-20 cm, 8.6/10.0 % for chum salmon 20-30 cm, and 8.8/10.3 % for pink salmon 10-25 cm. The prevalence of nekton or planktonic food does not affect on daily rhythm of feeding intensity: juvenile salmons feed mainly in the daytime, so they have the maximal index of stomachs fullness in the evening or early night (100-230 ‱, both in the warm and cold periods). Generally, the salmons prefer fish larvae and juveniles in conditions of low zooplankton abundance and large-sized zooplankton in conditions of its high abundance. Selectivity on euphausiids, hyperiids and pteropods is observed only in conditions of high zooplankton abundance and is an indicator of sufficient food supply.

Chaetognaths are ubiquitous marine zooplankton strongly influenced by oceanographic conditions. Epi-pelagic plankton samples taken across the Leeuwin Current system, the poleward flowing eastern boundary current of the Indian Ocean, were examined for chaetognath diversity and distribution. Sampling occurred at shelf, shelf break, and oceanic environments at each degree of latitude from 22 to 34°S. Nineteen species were identified, of which six are new records for the region with one an undescribed species. Low-moderate abundances (19.0 ± 2.4 individuals m−3) were observed compared with other eastern boundary currents and can be attributed to the unique oligotrophic nature of the system. The anomalous oceanography of the Leeuwin Current resulted in two distinct zoogeographic regions with distributions of tropical and temperate species separated around 28°S. Here, tropical waters transitioned to cooler, saltier waters and multivariate analyses identified temperature and salinity as the best indicators of community change. Community variation across the continental shelf was largely driven by one species, Flaccisagittaenflata, which was numerically dominant. Despite spatial variations, widely distributed species caused high overall community similarity. As the first system-wide investigation of Leeuwin Current Chaetognatha, this study provides benchmark biological information and highlights an unusual oceanography that produces a distinct planktonic zoogeography.

Correction: Table 1 and Table 2 were omitted in from the PDF of this article. On 29th April 2015 the two tables were included in the PDF and the page numbers were changed from 151-158 to 151-160.Eight groups of zooplankton were found at Sitakunda coast, Chittagong, northeastern part of the Bay of Bengal during January to June 2007. The identified groups were Appendicularia (2.46%), Chaetognatha (2.45%), Cladocera (2.31%), Copepoda (26.05%), Ctenophora (5.86%), Crustacean zooplankton (21.64%), Ichthyoplankton (17.77%) and Meroplankton (21.45%). Abundance of zooplankton varied from 413 to 7730 individuals/m3.Mangrove vegetate area (station- VI) has the highest abundant possibly due to the organic and inorganic matters dissolved in the water while ship breaking area (station- IV) has the lowest abundant. Zooplankton population was significantly (p>0.05) higher in the mangrove vegetate area than the fishermen community area and ship breaking area. The mangrove vegetate area has the highest composition (57.06%) of zooplankton than the fishers community area and ship breaking area (29.77% and 13.16%, respectively). Calanus sp. (12.29%) belonging to Copepods and fish eggs (9.25%) belonging to Ichthyoplankton were the most abundant and Oikopleura albicans (0.66%) from Appendicularia, Metapenaeus brevicornis (0.71%) and Metapenaeus monoceros (0.90%) belonging to Crustacean larvae were the lowest abundant species found at three major investigated area.Res. Agric., Livest. Fish.2(1): 151-160, April 2015

The paper is devoted to the Upper Cambrian and Tremadocian organophosphatic microfossils which were hitherto treated as conodonts and assigned mainly to the genera Coelocerodontus and Viirodus. Individual elements of the fossils, similarly to the elements of conodonts, belonged originally to the multi-element apparatuses. Present studies, based mainly on the collections from Sweden, Poland (core sections), Estonia and Kazakhstan, show that despite the similarities of their individual elements to conodonts, they significantly differ from them in the inner structure, as well as in the construction of the apparatuses composed of them. Elements of their apparatuses are matched in shape to each other and certainly functioned in conjunction, while those belonging to the euconodont apparatuses are usually differentiated in shape and usually functioned in separation. All fossils of this group are provisionally named coelocerodonts in this paper. Their individual elements, as well as the apparatuses composed of them, are similar in construction to those of the genus Phakelodus, which is an ancestor of chaetognaths.

The chaetognath species guild was analyzed from samples collected during the cruise of the German RV Victor Hensen to the Pacific coast of Costa Rica in December 1993 and February 1994. finding the following ten species of the genera Sagitta and Krohnitta: S.enflata, S. hexaplera, S. pacifica, S. neglecta, S. regularis, S. bedoti, S. friderici, S. popovicii, S. pulchra and K. pacifica. Because of their distributional patterns in the study area these species were ascribed to the following ecological groups: neritic, semi-neritic and oceanic. A strong gradient in species richness from offshore to inshore waters (810 one respectively) was found in both gulf systems. In shore chaetognaths were dominated by juveniles and adults of S. friderici in Golfo de Nicoya and by S. popovicii in Golfo Dulce. Biomass spectra were more continuous and of wider range in the Golfo Dulce area showing a dominance of larger chaetognaths. suggesting a more general developed pelagic system in Golfo Dulce, where larger chaetognaths might structure the plankton community by strong grazing pressure from above. Se analizó el gremio de los quetognatos con base en el muestreo hecho por el buque RV Victor Hensen al Pacífico costarricense en diciembre de 1993 y febrero de 1994. Se identificaron las siguientes diez especies de los géneros Sagitta y Krohnitta: S. enflata, S. hexaptera, S. pacifica, S. negluta, S. regularis, S. bedoti, S. friderici, S. popovicii, S. pulchra y K. pacifica. Sus patrones de distribución indican que pertenecen a los grupos ecológicos neríticos, semineríticos y oceánicos. En ambos golfos hubo un marcado gradiente de riqueza de especies desde mar afuera hacia la costa (8 a 1, respectivamente) Los quetognatos de la parte interna fueron principalmente juveniles y adultos de S. friderici en el Golfo de Nicoya y S. popovicii en el Golfo Dulce. Los espectros de biomasa fueron más contínuos y de mayor ambito en el area del Golfo Dulce, donde dominaron las especies más grandes, lo que sugiere un sistema pelágico más desarrollado en el Golfo Dulce, donde los quetognatos más grandes pueden definir la estructura de la comunidad del plancton mediante fuerte presión de depredación desde la parte superior del sistema.

The extent of within-species genetic variation across the diversity of animal life is an underexplored problem in ecology and evolution. Although neutral genetic variation should scale positively with population size, mitochondrial diversity levels are believed to show little variation across animal species. Here, we report an unprecedented case of extreme mitochondrial diversity within natural populations of two morphospecies of chaetognaths (arrow worms). We determine that this diversity is composed of deep sympatric mitochondrial lineages, which are in some cases as divergent as human and platypus. Additionally, based on 54 complete mitogenomes, we observed mitochondrial gene order differences between several of these lineages. We examined nuclear divergence patterns (18S, 28S, and an intron) to determine the possible origin of these lineages, but did not find congruent patterns between mitochondrial and nuclear markers. We also show that extreme mitochondrial divergence in chaetognaths is not driven by positive selection. Hence, we propose that the extreme levels of mitochondrial variation could be the result of either a complex scenario of reproductive isolation, or a combination of large population size and accelerated mitochondrial mutation rate. These findings emphasize the importance of characterizing genome-wide levels of nuclear variation in these species and promote chaetognaths as a remarkable model to study mitochondrial evolution.

The capability of animals to emit light, called bioluminescence, is considered to be a major factor in ecological interactions. Because it occurs across diverse taxa, measurements of bioluminescence can be powerful to detect and quantify organisms in the ocean. In this study, 17 years of video observations were recorded by remotely operated vehicles during surveys off the California Coast, from the surface down to 3,900 m depth. More than 350,000 observations are classified for their bioluminescence capability based on literature descriptions. The organisms represented 553 phylogenetic concepts (species, genera or families, at the most precise taxonomic level defined from the images), distributed within 13 broader taxonomic categories. The importance of bioluminescent marine taxa is highlighted in the water column, as we showed that 76% of the observed individuals have bioluminescence capability. More than 97% of Cnidarians were bioluminescent, and 9 of the 13 taxonomic categories were found to be bioluminescent dominant. The percentage of bioluminescent animals is remarkably uniform over depth. Moreover, the proportion of bioluminescent and non-bioluminescent animals within taxonomic groups changes with depth for Ctenophora, Scyphozoa, Chaetognatha, and Crustacea. Given these results, bioluminescence has to be considered an important ecological trait from the surface to the deep-sea.

Summary Chaetognaths (arrow worms) are a separate phylum (Chaetognatha) of small carnivorous animals, dominantly pelagic, and a major component of today's plankton [1, 2]. The position of Chaetognatha among metazoan phyla remains equivocal—neither morphological nor molecular data provide definitive evidence [3]. Originating early in the Cambrian period [4], if not earlier [5], chaetognaths quickly became important members of marine metazoan communities [6]. Chaetognath grasping spines, originally reported as conodonts, occur worldwide in many Cambrian marine sediments [6, 7]. Fossilized chaetognath bodies, in contrast, are very rare: only two unequivocal specimens have been reported, both from the early Cambrian of China [8, 9]. Here we describe Capinatator praetermissus , a new genus and species, based on ∼50 specimens from several middle Cambrian Burgess Shale localities in British Columbia, many of which preserve evidence of soft tissues. Capinatator praetermissus reached body lengths of nearly 10 cm exclusive of fins, a much larger size than that of most living forms. Clusters of specimens preserving the body indicate that they were rapidly buried, providing indirect evidence that they swam near the seabed. The feeding apparatus comprises up to ∼25 spines in each half, almost double the maximum number in living chaetognaths. Early chaetognaths apparently occupied ecological niches associated with predatory euarthropods. The large body size and high number of grasping spines in C. praetermissus may indicate that miniaturization and migration to a planktonic lifestyle were secondary.

Zooplankton are the link connecting primary producers to higher trophic levels, and knowing their distribution and community is important for predicting the distribution of predator species, like fish, seabirds, and marine mammals. However, data from open Arctic oceans are still scarce. In autumn, tens of millions of the planktivorous little auks (Alle alle) (about 75 % of the world’s population) and millions of thick-billed murres (Uria lomvia) pass through the Baffin Bay. To investigate their potential food sources, we investigated the spatial and vertical distribution of zooplankton and small fishes in the upper 500 m of southern Baffin Bay in September 2009. The zooplankton community was dominated by copepods (55 % of abundance in the upper 500 m), primarily of the genus Calanus. Other important zooplankton taxa included Limacina helicina, Chaetognatha, and Cirripedia nauplii. On the Greenland Shelf, most Calanus were late copepodite stages and most were found at the depths of >200 m, suggesting they were in diapause. On the Canadian Shelf, there were relatively more Calanus in the near-surface layers, which were probably still actively feeding and which were available to visual predators such as seabirds and fish. The acoustic survey showed the highest density of polar cod Boreogadus saida in the upper 50 m on the western part of the Greenland Shelf. A particularly high biomass of both zooplankton and polar cod was found in the central part of the basin in association with a local relatively shallow area.