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Aim: Mesoplankton of the Southern Ocean is the key trophic link between phytoplankton and other consumers and an important part of the biological carbon pump, a critical component of climate regulation. Although general patterns of mesoplankton distribution and life cycles are known, we still cannot estimate mesoplankton standing stocks at specified ocean‐basin scales. Location: Southern Ocean, 34.4−56.9°S, 0–14.4°E. Time period: December 2009. Major taxa studied: All mesoplankton 0.2–20.0 mm. Methods: We assessed biomass of dominant taxa and total wet mesoplankton biomass (B, mg/m3) using surface chlorophyll a concentration (Chl) as a proxy of phytoplankton biomass and surface temperature (ST), a basic hydrological parameter. We sampled three strata within the layer 0–300 m at 43 stations with a Judey net (0.1 m2, 180 µm). Results: We identified 163 taxa and calculated their biomass, biomass of major trophic groups, and total mesoplankton biomass. Monthly Chl and ST derived from satellite imaging were averaged at various temporal and spatial scales. B in the upper layer and in the integrated layer 0–300 m was significantly linked to antecedent Chl signals; the most significant regressions were found between B and monthly Chl and ST averaged two months prior to the survey and 10° upstream of the Antarctic Circumpolar Current. Larger mesoplankton fractions showed longer response periods to Chl signal than smaller fractions. Main conclusions: Our results suggest the integral mesoplankton stock is 2.47–3.69 Gt wet weight wtot (ww), or 0.12–0.18 Gt C, in the whole Southern Ocean. Mesoplankton was dominated by omnivores (69%–74%) followed by carnivores (25%) and herbivores (20%), which suggests the leading role of omnivory in the Southern Ocean pelagic during the austral summer. We anticipate that these results will help to provide a deeper insight into the Southern Ocean ecosystems and will benefit models predicting changes in the carbon–climate Earth system. [ABSTRACT FROM AUTHOR]

The shrimp genera Ephyrina, Meningodora and Notostomus have an unusual carapace strengthened with carinae and a half-serrated mandible, which may suggest a possible monophyly of this group. Here we test this hypothesis and present the first phylogenetic study of these genera based on 95 morphological characters (all valid species coded) and six molecular markers (71% of valid species sequenced). Representatives of all genera of Oplophoridae (sister to Acanthephyridae) were outgroups, 32 species belonging to all genera and potentially different clades of Acanthephyridae were ingroups. Both morphological and molecular analyses retrieve trees with similar topology. Our results reject the hypothesis of a clade formed by Ephyrina + Meningodora + Notostomus. We show that Ephyrina and Notostomus are monophyletic, both on morphological and on molecular trees, Meningodora gains support only on morphological trees. Evolutionary traits in the Ephyrina and Meningodora + Notostomus clades are different. Synapomorphies are mostly linked to adaptations to forward motion in Ephyrina (oar-like meri and ischia of pereopods, stempost-like rostrum) and to progressive strengthening of the carapace and pleon in Meningodora and Notostomus (net of sharp carinae). Unusual mandibles evolved in the clades independently and represent convergent adaptations to feeding on gelatinous organisms. [ABSTRACT FROM AUTHOR]

A phylogenetic study of deep-sea dendrobranchiate genera Altelatipes , Benthesicymus and Benthonectes based on four molecular markers and 91 morphological characters is presented. All currently recognized species of these genera, representatives of all other genera and species groups of Benthesicymidae, and three outgroups were included in the analyses. The molecular and morphological methods retrieved similar results, the molecular methods provided better resolution of deeper nodes and higher clade support. Both types of analyses showed paraphyly of Benthesicymus , which encompass five robust clades, four of which are diagnosed as new genera (type species in parentheses): Benthesicymus s.s. (B. crenatus), Bathicaris gen. nov. (Benthesicymus brasiliensis), Dalicaris gen. nov. (Benthesicymus altus), Trichocaris gen. nov. (Benthesicymus bartletti) and Maorrancaris gen. nov. (Benthesicymus investigatoris). Altelatipes was found to be monophyletic. The evolution of the major clades of Benthesicymidae is shown to be linked to trophic specialization, while further divergence at the genus level is mainly related to sexual evolution seen in the elaboration of the copulatory structures. We provide amended diagnoses of the previously recognized and new genera, key to species of each of these genera and include an updated key to genera of Benthesicymidae. [ABSTRACT FROM AUTHOR]

The first comprehensive phylogenetic study of the family Oplophoridae is based on four molecular markers and 87 morphological characters. We have examined and coded five major groups of morphological characters related to the rostrum (nine characters), the carapace (10), the abdomen and telson (34), the exopods (eight) and the armature of the posteriormost three pereopods (22). Abdomen/telson-linked characters are the most important in support of genus level and species-group level clades; abdomen/telson-linked, rostrum-linked characters and the armature of the last three pereopods explain the main bulk of speciation. Four robustly supported species groups within Systellaspis are designated: the S. debilis species group, the S. cristata species group, the S. braueri species group and the S. pellucida species group. We provide an amended key to all genera, species groups and species of Oplophoridae. We reveal three groups of morphological characters, which are likely coupled with the same locomotive function and thus evolved as a single unit: carapace, abdomen and exopods. We show that the armature of the posteriormost three pereopods evolved independently of other characters and suggest that this group is linked to such biological roles as mating and grooming. [ABSTRACT FROM AUTHOR]

The first comprehensive phylogenetic study of Euphausiacea (all 86 valid species) is presented. It is based on four molecular markers and 168 morphological characters (including 58 characters of the petasma). Phylogenetic analyses support the monophyly and robustness of the families Bentheuphausidae and Euphausiidae and reveal three major clades for which we erect three new subfamilies: Thysanopodinae, Euphausiinae and Nematoscelinae. All genus‐level clades are statistically supported (except Thysanopoda in molecular analyses), deeply nested within the subfamily‐level clades, and encompass 14 new species groups. Copulatory structures have a major impact on tree topology in the morphological analysis, the removal of which resulted in only half the number of supported clades and genera. We revealed three groups of morphological characters, which are probably coupled with the same biological role and thus interlinked evolutionarily: (i) antennular peduncle and petasma (copulation); (ii) eyes and anterior thoracopods (feeding); and (iii) shape of carapace and pleon (defence). We analysed the evolutionary pathways of the clades into main oceanic biotopes and compared them with morphological adaptations most likely to be coupled with this process. [ABSTRACT FROM AUTHOR]

Despite their role in marine systems, Sergestidae remain one of the most poorly understood families amongst planktonic shrimps with regard to phylogeny. Recent morphological and phylogenetic revisions of a number of sergestid genera have disentangled classificatory problems and emphasized the importance of reproductive structures for the taxonomy and phylogeny of the Sergestidae. Only three genera, A cetes, P eisos, and S icyonella, remain unrevised phylogenetically. We undertook a phylogenetic analysis of these groups based on 124 morphological characters (120 binary, four multistate). Eighteen new characters were based on scanning electron microscopy studies of the clasping organ and petasma. The phylogenetic analysis revealed statistically supported monophyly of the clades S icyonella and A cetes + P eisos. We combine P eisos and A cetes into a monophyletic genus A cetes, give emended diagnoses and keys to all species of S icyonella and A cetes, and discuss morphological trends within these genera. We present maps of geographical distribution for all valid species of A cetes. © 2015 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Petalidium ( Decapoda: Dendrobranchiata: Sergestidae) is one of the least known genera of pelagic decapods. On the basis of collections taken during Dana Expedition 1920-22 and 1928-30, we revise the morphology of the genus. To understand the taxonomic status and position of Petalidium within other sergestid genera, we used 150 morphological characters (127 binary, 23 multistate). Three recognized species of Petalidium and eighteen type species representing all other genera of Sergestidae were included as terminals. Characters were polarized using Lucifer typus ( Luciferidae: Sergestoidea) and Aristeomorpha foliacea ( Aristeidae: Penaeoidea) as the outgroups. Phylogenetic analysis revealed monophyly of Petalidium comprising three species: Petalidium foliaceum Bate, 1881; Petalidium obesum ( Krøyer, 1859); and Petalidium suspiriosum Burkenroad, 1937. Phylogenetic analyses also revealed possible monophyly of the clade including 15 new genera of the former Sergia and Sergestes and the position of Lucifer (family Luciferidae) within the clade Sergestidae. These results highlight necessity of future phylogenetic analyses of the remaining genera Lucifer, Acetes, Peisos, and Sicyonella involving all species of these genera and promise interesting changes for the classification of Sergestoidea. Morphological trends within Sergestoidea are discussed, and an emended diagnosis of Petalidium and diagnoses of the species it includes are given. All species are illustrated and biology of the genus is discussed. Keys to species of Petalidium based upon new information are presented. © 2015 The Linnean Society of London [ABSTRACT FROM AUTHOR]