Trophic Dynamics and Feeding Ecology of Skipjack Tuna (Katsuwonus pelamis) off Eastern and Western Taiwan.

The skipjack tuna (Katsuwonus pelamis) is a mesopredator fish species with seasonal abundance in waters off Taiwan. Regional ecological and life-history information has been historically lacking for this species. In recent years, stable isotope analysis (SIA) of carbon and nitrogen has been used to assess predator feeding ecology and broader ecosystem trophic dynamics. This study evaluated comparative skipjack feeding ecology in distinct regions off Taiwan, combining traditional stomach content analysis with SIA of individuals off western (n = 43; 2020) and eastern (n = 347; 2012-2014 and n = 167; 2020) Taiwan. The stomach content analysis showed the most important prey to be ponyfish (Photopectoralis bindus) in western Taiwan and epipelagic squids (Myopsina spp.) and carangids (Decapterus macrosoma;) in eastern Taiwan from 2012 to 2014 and epipelagic carangids (Decapterus spp.) and flying fishes (Cheilopogon spp.) in eastern Taiwan in 2020, suggesting that the skipjack tuna is a generalist predator across regions. In contrast, time-integrated diet estimates from Bayesian mixing models indicated the importance of cephalopods and crustaceans as prey, potentially demonstrating more mesopelagic feeding in less productive waters during skipjack migrations outside the study regions. Skipjack off western Taiwan had a slightly higher estimated trophic position than in the waters off eastern Taiwan, potentially driven by the varying nutrient-driven pelagic food web structures. Skipjack SI values increased with body size off eastern Taiwan but not in western waters, suggesting that opportunistic predation can still result in different predator-prey size dynamics between regions.

Revisiting the phylogeny of the genus Lolliguncula Steenstrup 1881 improves understanding of their biogeography and proves the validity of Lolliguncula argus Brakoniecki & Roper, 1985.

The biogeography of American loliginid squids has been improved in recent years, but certain key taxa have been missing. Given that the most accurate phylogenies and estimates of divergence times of common ancestors depend heavily on good taxonomic coverage we have reanalyzed the genus Lolliguncula in light of new samples that increase the geographic and taxonomic coverage. New sequences were produced using standard methods to update an existing dataset for COI, 16S and Rhodopsin markers. Data was analyzed using various species delimitation methods, rigorous phylogenetic analyses and estimates of divergence times between clades. Within Lolliguncula we recover five monophyletic lineages that relate to the known species L. argus, L. diomedeae, L. panamensis, L. brevis North Atlantic and L. brevis South Atlantic. Except when using low divergence thresholds in ABGD, species delimitation methods only identify four of these lineages as distinct species, grouping L. argus and L. diomedeae as a single species. However, considering the reciprocal monophyly, recent divergence time estimate and morphological diagnoses we refrain from synonymizing L. argus within L. diomedeae, considering them very recently diverged species. The biogeography of the American loliginids is discussed, wherein basal cladogenesis in both Lolliguncula and Doryteuthis occur between the Atlantic and Pacific about 45 mya, with subsequent speciation around 20 mya associated with seafloor changes during the formation of the Caribbean. The recent speciation between L. argus and L. diomedeae is associated to oceanic environmental changes associated with glaciation, deep sea cooling and tropical upwelling.

Phylogenomic analyses recover a clade of large-bodied decapodiform cephalopods.

Phylogenetic relationships among the squids and cuttlefishes (Cephalopoda:Decapodiformes) have resisted clarification for decades, despite multiple analyses of morphological, molecular and combined data sets. More recently, analyses of complete mitochondrial genomes and hundreds of nuclear loci have yielded similarly ambiguous results. In this study, we re-evaluate hypotheses of decapodiform relationships by increasing taxonomic breadth and utilizing higher-quality genome and transcriptome data for several taxa. We also employ analytical approaches to (1) identify contamination in transcriptome data, (2) better assess model adequacy, and (3) account for potential biases. Using this larger data set, we consistently recover a clade comprising Myopsida (closed-eye squid), Sepiida (cuttlefishes), and Oegopsida (open-eye squid) that is sister to a Sepiolida (bobtail and bottletail squid) clade. Idiosepiida (pygmy squid) is consistently recovered as the sister group to all sampled decapodiform lineages. Further, a weighted Shimodaira-Hasegawa test applied to one of our larger data matrices rejects all alternatives to these ordinal-level relationships. At present, available nuclear genome-scale data support nested clades of relatively large-bodied decapodiform cephalopods to the exclusion of pygmy squids, but improved taxon sampling and additional genomic data will be needed to test these novel hypotheses rigorously.

The grass squid Pickfordiateuthis pulchella is a paedomorphic loliginid.

The wide disparity in adult body size observed both within and among animal taxa has long attracted widespread interest, with several general rules having been proposed to explain trends in body size evolution. Adult body size disparity among the cephalopod mollusks is remarkable, with adult body sizes ranging from a few centimeters to several meters. Some of the smallest cephalopods are found within Pickfordiateuthis, a group comprising three described species of squid found in the western Atlantic and tropical eastern Pacific. Pickfordiateuthis pulchella, the type species of the genus, was initially proposed to be closely related to the loliginid squids (Loliginidae), with subsequent descriptions of additional species supporting a placement within Loliginidae. Pickfordiateuthis is remarkable in that all species reach sexual maturity at about one-fifth to one-tenth the size seen in most loliginid species. To date, no phylogenetic analyses have included representatives of Pickfordiateuthis. To infer the phylogenetic position of Pickfordiateuthis and explore its implications for body size evolution, we collected specimens of Pickfordiateuthis pulchella from Brazilian waters and sequenced regions of two loci-the mitochondrial large ribosomal subunit (rrnL a.k.a. 16S) gene and the nuclear gene rhodopsin. Maximum likelihood and Bayesian analyses of these sequences support a placement of Pickfordiateuthis pulchella as sister to a clade comprising the Western Hemisphere loliginid genera Doryteuthis and Lolliguncula. Analyses of body size evolution within Loliginidae suggest that a shift to a smaller body size optimum occurred along the lineage leading to P. pulchella, with some evidence of shifts toward larger sizes in the ancestors of Loligo and Sepioteuthis; these inferences seem to be robust to phylogenetic uncertainty and incomplete taxon sampling. The small size and juvenile-like morphological traits seen in adult Pickfordiateuthis (e.g., sepiolid-like fins and biserial sucker arrangement in the tentacles) may be due to paedomorphosis.

Phylogenetic relationships and cryptic species in the genus Sthenoteuthis (Cephalopoda: Ommastrephidae) in the South China Sea.

Large squids of the genus Sthenoteuthis are commercially relevant species that include two truly oceanic squids. They are large nektonic predators being widely distributed throughout tropical and subtropical waters of the Atlantic and Indo-Pacific Ocean. The present study investigates different morphs varying in size at maturity, and assesses the genetic divergence in Sthenotheutis in relation to geographic patterns in the South China Sea. We obtained sequences using a mitochondrial (cytochrome c oxidase subunit I) and a nuclear (Histone H3) gene marker from 111 individuals in 23 locations of the South China Sea. In combination with sequences available in public databases, we performed tests on DNA taxonomy, mostly based on molecular phylogenies. Our results suggest that the genus Sthenoteuthis includes at least three species. The Indo-Pacific purpleback squid Sthenoteuthis oualaniensis contains at least two genetically distinct lineages that can be considered separate species, a dwarf species and a medium-sized species, separated by both the mitochondrial marker and the more conserved nuclear marker. We also assessed whether the few cases of mitonuclear discordance could be the result of genetic introgression and past hybridization or incongruence lineage sorting. The medium-sized species is more widely distributed and dominant in the South China Sea than the dwarf species. The medium-sized species inhabits the whole South China Sea, whereas the dwarf species is restricted to the equatorial waters of the South China Sea. The medium-sized species has two further genetic clades, one distributed in the East Pacific Ocean and the other in the South China Sea. This high level of genetic differentiation is in agreement with the discriminant analysis on the morphological measurements, clearly separating the dwarf and medium-sized species, indicating the presence of a complex of pseudo-cryptic species in S. oualaniensis, clearly identifiable by differences in DNA sequences and in body size, and statistically differentiated in their body measurements.

Assessing the utility of transcriptome data for inferring phylogenetic relationships among coleoid cephalopods.

Historically, deep-level relationships within the molluscan class Cephalopoda (squids, cuttlefishes, octopods and their relatives) have remained elusive due in part to the considerable morphological diversity of extant taxa, a limited fossil record for species that lack a calcareous shell and difficulties in sampling open ocean taxa. Many conflicts identified by morphologists in the early 1900s remain unresolved today in spite of advances in morphological, molecular and analytical methods. In this study we assess the utility of transcriptome data for resolving cephalopod phylogeny, with special focus on the orders of Decapodiformes (open-eye squids, bobtail squids, cuttlefishes and relatives). To do so, we took new and previously published transcriptome data and used a unique cephalopod core ortholog set to generate a dataset that was subjected to an array of filtering and analytical methods to assess the impacts of: taxon sampling, ortholog number, compositional and rate heterogeneity and incongruence across loci. Analyses indicated that datasets that maximized taxonomic coverage but included fewer orthologs were less stable than datasets that sacrificed taxon sampling to increase the number of orthologs. Clades recovered irrespective of dataset, filtering or analytical method included Octopodiformes (Vampyroteuthis infernalis + octopods), Decapodiformes (squids, cuttlefishes and their relatives), and orders Oegopsida (open-eyed squids) and Myopsida (e.g., loliginid squids). Ordinal-level relationships within Decapodiformes were the most susceptible to dataset perturbation, further emphasizing the challenges associated with uncovering relationships at deep nodes in the cephalopod tree of life.

Updated molecular phylogeny of the squid family Ommastrephidae: Insights into the evolution of spawning strategies.

Two types of spawning strategy have been described for ommastrephid squids: coastal and oceanic. It has been suggested that ancestral ommastrephids inhabited coastal waters and expanded their distribution into the open ocean during global changes in ocean circulation in the Oligocene. This hypothesis could explain the different reproductive strategies in oceanic squids, but has never been tested in a phylogenetic context. In the present study, we assess the coastal-to-open-ocean hypothesis through inferring the evolution of reproductive traits (spawning type) of ommastrephid squids using the phylogenetic comparative method to estimate ancestral states and divergence times. This analysis was performed using a robust molecular phylogeny with three mitochondrial genes (COI, CYTB and 16S) and two nuclear genes (RHO and 18S) for nearly all species of ommastrephid squid. Our results support dividing the Ommastrephidae into the three traditional subfamilies, plus the monotypic subfamily Todaropsinae as proposed previously. Divergence times were found to be older than those suggested. Our analyses strongly suggest that early ommastrephid squids spawned in coastal areas, with some species subsequently switching to spawn in oceanic areas, supporting previous non-tested hypotheses. We found evidence of gradual evolution change of spawning type in ommastrephid squids estimated to have occurred since the Cretaceous.

Potential use of stable isotope and fatty acid analyses for traceability of geographic origins of jumbo squid (Dosidicus gigas).

RATIONALE: Squid is an important seafood resource for Asian and European countries. With the continuous development of processed squid products, an effective traceability system has become increasingly prominent. Here, we attempt to trace the fishery products of the main target species, jumbo squid (Dosidicus gigas), by using biochemical tracers. METHODS: Carbon and nitrogen isotope ratios (δ13 C and δ15 N values) and fatty acid profiles were identified in squid from three harvest locations in the eastern Pacific Ocean by isotope ratio mass spectrometry and gas chromatography/mass spectrometry, respectively. Comparative analysis was used to evaluate the geographic variations in tracers and to identify the suitable discriminatory variables among origins. RESULTS: Significant spatial variations were found in isotopic values and fatty acid profiles in squid muscle tissues, possibly because of different food availability and/or oceanographic conditions that each group experiences at a given location. The stepwise discriminant analysis indicated that δ15 N, C16:1n7, C17:1n7, C18:2n6, C20:1 and C20:4n6 were effective variables at differentiating origin. CONCLUSIONS: Combined use of stable isotope ratios and fatty acid analyses could trace geographic origins of jumbo squid. This study provides an alternative approach for improving authenticity evaluation of commercial squid products.

Whole mitochondrial genome of the Ram's Horn Squid shines light on the phylogenetic position of the monotypic order Spirulida (Haeckel, 1896).

The phylogenetic position of the only known species within the order Spirulida, the Ram's Horn Squid, Spirula spirula, may be the key to resolving relationships within Decapodiformes (squids and cuttlefishes). Spirula spirula possesses several unique features including an internal calcareous chambered shell unlike the familiar cuttlebone of Sepiidae (cuttlefishes). The shell is reduced to a gladius or absent in other decapod clades. To resolve decapodiform phylogenetic relationships we sequenced the mitochondrial genome of S. spirula and Sepiadarium austrinum and analysed these along with other mitochondrial genomes. Sequence analyses found that S. spirula and Sepiidae, the only two extant phragmocone bearing groups, were not sister taxa. Rather, in most analyses S. spirula was placed within a clade containing Bathyteuthoidea and Oegopsida either as the sister taxon to Bathyteuthoidea+Oegopsida or the sister taxon to Bathyteuthoidea only, depending upon the analysis method. Sepiidae was the sister taxon to a clade containing all remaining decapods. Spirulid mitochondrial gene order was identical to that of Octopodiformes, which we recognize as close to that of ancestral molluscs. The phylogenetic position of Idiosepiidae differed among analysis methods of molecular sequence data. However, gene order analysis resolved a highly supported monophyletic relationship containing Idiosepiidae and Sepiolida.

Identification of four squid species by quantitative real-time polymerase chain reaction.

Squids are distributed worldwide, including many species of commercial importance, and they are often made into varieties of flavor foods. The rapid identification methods for squid species especially their processed products, however, have not been well developed. In this study, quantitative real-time PCR (qPCR) systems based on specific primers and TaqMan probes have been established for rapid and accurate identification of four common squid species (Ommastrephes bartramii, Dosidicus gigas, Illex argentinus, Todarodes pacificus) in Chinese domestic market. After analyzing mitochondrial genes reported in GenBank, the mitochondrial cytochrome b (Cytb) gene was selected for O. bartramii detection, cytochrome c oxidase subunit I (COI) gene for D. gigas and T. Pacificus detection, ATPase subunit 6 (ATPase 6) gene for I. Argentinus detection, and 12S ribosomal RNA (12S rDNA) gene for designing Ommastrephidae-specific primers and probe. As a result, all the TaqMan systems are of good performance, and efficiency of each reaction was calculated by making standard curves. This method could detect target species either in single or mixed squid specimen, and it was applied to identify 12 squid processed products successfully. Thus, it would play an important role in fulfilling labeling regulations and squid fishery control.

Material properties of Pacific hake, Humboldt squid, and two species of myctophids in the California Current.

Material properties of the flesh from three fish species (Merluccius productus, Symbolophorus californiensis, and Diaphus theta), and several body parts of the Humboldt squid (Dosidicus gigas) collected from the California Current ecosystem were measured. The density contrast relative to seawater varied within and among taxa for fish flesh (0.9919-1.036), squid soft body parts (mantle, arms, tentacle, braincase, eyes; 1.009-1.057), and squid hard body parts (beak and pen; 1.085-1.459). Effects of animal length and environmental conditions on nekton density contrast were investigated. The sound speed contrast relative to seawater varied within and among taxa for fish flesh (0.986-1.027) and Humboldt squid mantle and braincase (0.937-1.028). Material properties in this study are similar to values from previous studies on species with similar life histories. In general, the sound speed and density of soft body parts of fish and squid were 1%-3% and 1%-6%, respectively, greater than the surrounding seawater. Hard parts of the squid were significantly more dense (6%-46%) than seawater. The material properties reported here can be used to improve target strength estimates from acoustic scattering models, which could increase the accuracy of biomass estimates from acoustic surveys for these nekton.

Development of polymorphic expressed sequence tag-single sequence repeat markers in the common Chinese cuttlefish, Sepiella maindroni.

The common Chinese cuttlefish (Sepiella maindroni) is one of the popular edible cephalopod consumed across Asia. To facilitate the population genetic investigation of this species, we developed fourteen polymorphic microsatellite makers from expressed sequence tags of S. maindroni. The number of alleles at each locus ranged from 6 to 10 with an average of 7.9 alleles per locus. The ranges of observed and expected heterozygosity were from 0.615 to 0.962 and 0.685 to 0.888, respectively. Four loci were found deviated significantly from Hardy-Weinberg equilibrium. The polymorphism information content ranged from 0.638 to 0.833. These polymorphic microsatellite loci will be helpful for the population genetic, genetic linkage map, and other genetic studies of S. maindroni.

Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species.

Despite its charismatic appeal to both scientists and the general public, remarkably little is known about the giant squid Architeuthis, one of the largest of the invertebrates. Although specimens of Architeuthis are becoming more readily available owing to the advancement of deep-sea fishing techniques, considerable controversy exists with regard to topics as varied as their taxonomy, biology and even behaviour. In this study, we have characterized the mitochondrial genome (mitogenome) diversity of 43 Architeuthis samples collected from across the range of the species, in order to use genetic information to provide new and otherwise difficult to obtain insights into the life of this animal. The results show no detectable phylogenetic structure at the mitochondrial level and, furthermore, that the level of nucleotide diversity is exceptionally low. These observations are consistent with the hypotheses that there is only one global species of giant squid, Architeuthis dux (Steenstrup, 1857), and that it is highly vagile, possibly dispersing through both a drifting paralarval stage and migration of larger individuals. Demographic history analyses of the genetic data suggest that there has been a recent population expansion or selective sweep, which may explain the low level of genetic diversity.

The complete mitochondrial genomes of deep-sea squid (Bathyteuthis abyssicola), bob-tail squid (Semirossia patagonica) and four giant cuttlefish (Sepia apama, S. latimanus, S. lycidas and S. pharaonis), and their application to the phylogenetic analysis of Decapodiformes.

We determined the complete mitochondrial (mt) genomes of the deep-sea squid (Bathyteuthis abyssicola; supperfamily Bathyteuthoidea), the bob-tail squid (Semirossia patagonica; order Sepiolida) and four giant cuttlefish (Sepia apama, S. latimanus, S. lycidas and S. pharaonis; order Sepiida). The unique structures of the mt genomes of Bathyteuthis and Semirossia provide new information about the evolution of decapodiform mt genomes. We show that the mt genome of B. abyssicola, like those of other oegopsids studied so far, has two long duplicated regions that include seven genes (COX1-3, ATP6 and ATP8, tRNA(Asn), and either ND2 or ND3) and that one of the duplicated COX3 genes has lost its function. The mt genome of S. patagonica is unlike any other decapodiforms and, like Nautilus, its ATP6 and ATP8 genes are not adjacent to each other. The four giant cuttlefish have identical mt gene order to other cuttlefish determined to date. Molecular phylogenetic analyses using maximum likelihood and Bayesian methods suggest that traditional order Sepioidea (Sepiolida+Sepiida) is paraphyletic and Sepia (cuttlefish) has the sister-relationship with all other decapodiforms. Taking both the phylogenetic analyses and the mt gene order analyses into account, it is likely that the octopus-type mt genome is an ancestral state and that it had maintained from at least the Cephalopoda ancestor to the common ancestor of Oegopsida, Myopsida and Sepiolida.

New molecular phylogeny of the squids of the family Loliginidae with emphasis on the genus Doryteuthis Naef, 1912: mitochondrial and nuclear sequences indicate the presence of cryptic species in the southern Atlantic Ocean.

The family Loliginidae Lesueur, 1821, is currently considered to include seven genera and approximately 50 species of neritic and coastal squids. These commercially important species occur in tropical and temperate coastal waters around the world. The taxonomy of the family has been revised a number of times in recent years, focusing in particular on genera such as Doryteuthis, Sepioteuthis, Alloteuthis, and Uroteuthis, which are represented by populations in the New World, Oceania, Europe/Africa, and Asia. However, no detailed phylogenetic analysis is available for the loliginids of the southern Atlantic, in particular the genus Doryteuthis. The present molecular study analyzed 81 loliginid taxa from around the world. The partial sequencing of the mitochondrial 16S and Cytochrome Oxidase I genes, and the nuclear rhodopsin gene revealed a number of important patterns, recovering the monophyletic status of the majority of the genera and revealing possible cryptic species in Doryteuthis plei D. pealei, Uroteuthis duvauceli and Sepioteuthis lessoniana.

Morphological and morphometric variability of the squid Lolliguncula brevis (Mollusca: Cephalopoda) in Brazilian waters: evidence for two species in the Western Atlantic?

Morphological and morphometric variability of the small-sized coastal squid Lolliguncula brevis was assessed along the largest part of its latitudinal range in the southern hemisphere, off the Brazilian coast (8º S - 27º S). A general homogeneity in form was found throughout the entire latitudinal range. In terms of body proportions, no latitudinal gradients were evident, but a few local "morphotypes" could be distinguished. The distinctive egg mass morphology, and size and form features, including a hectocotylus 20-40% longer than the opposing ventral arm and the presence of suckers on the buccal membrane, indicated that Lolliguncula from northern and southern hemispheres might comprise two different taxa.

Phylogenomics illuminates the evolution of bobtail and bottletail squid (order Sepiolida).

Bobtail and bottletail squid are small cephalopods with striking anti-predatory defensive mechanisms, bioluminescence, and complex morphology; that inhabit nektobenthic and pelagic environments around the world's oceans. Yet, the evolution and diversification of these animals remain unclear. Here, we used shallow genome sequencing of thirty-two bobtail and bottletail squids to estimate their evolutionary relationships and divergence time. Our phylogenetic analyses show that each of Sepiadariidae, Sepiolidae, and the three subfamilies of the Sepiolidae are monophyletic. We found that the ancestor of the Sepiolinae very likely possessed a bilobed light organ with bacteriogenic luminescence. Sepiolinae forms a sister group to Rossinae and Heteroteuthinae, and split into Indo-Pacific and Atlantic-Mediterranean lineages. The origin of these lineages coincides with the end of the Tethys Sea and the separation of these regions during the Eocene and the beginning of the Oligocene. We demonstrated that sepiolids radiated after the Late Cretaceous and that major biogeographic events might have shaped their distribution and speciation.

Molecular inference of phylogenetic relationships among Decapodiformes (Mollusca: Cephalopoda) with special focus on the squid order Oegopsida.

Squids, cuttlefish and bobtail squids comprise the molluscan superorder Decapodiformes (Mollusca: Cephalopoda). Although these animals exemplify the morphological and ecological diversity seen in Cephalopoda, no previous study has focused resolving decapodiform relationships, particularly within Oegopsida, a large order comprised of pelagic squid. To further clarify the phylogenetic history of Decapodiformes, and Oegopsida in particular, molecular data for five genes (18S rRNA, 28S rRNA, Histone H3, 16S rRNA, COI) was collected for 90 taxa representing all major lineages and families and evaluated using parsimony, likelihood, and Bayesian analysis. Although ordinal relationships were sensitive to analytical method, several conclusions can be inferred: the pelagic order Myopsida is closely related to the benthic sepioids, whose relationships were ambiguous, and Bathyteuthoidea is distinct from Oegopsida. Within Oegopsida several clades are consistently recovered, some with previous morphological support (e.g. chiroteuthid, lepidoteuthid, histioteuthid families) while others suggest novel relationships (e.g. Architeuthidae+Neoteuthidae). This study, with its broad coverage of taxa, provides the first in-depth analysis of Decapodiformes with special focus on the morphologically and biogeographically diverse Oegopsida, confirms several sister-taxon relationships, and provides new hypotheses of cephalopod evolution in the open ocean.

Long-term changes in habitat and trophic level of Southern Ocean squid in relation to environmental conditions.

Long-term studies of pelagic nekton in the Southern Ocean and their responses to ongoing environmental change are rare. Using stable isotope ratios measured in squid beaks recovered from diet samples of wandering albatrosses Diomedea exulans, we assessed decadal variation (from 1976 to 2016) in the habitat (δ13C) and trophic level (δ15N) of five important Southern Ocean squid species in relation to indices of environmental conditions-Southern Oscillation Index (SOI) and Southern Annular Mode (SAM). Based on δ13C values, corrected for the Suess effect, habitat had changed over the last 50 years for Taonius sp. B (Voss), Gonatus antarcticus, Galiteuthis glacialis and Histioteuthis atlantica but not Moroteuthopsis longimana. By comparison, mean δ15N values were similar across decades for all five species, suggesting minimal changes in trophic levels. Both SAM and SOI have increased in strength and frequency over the study period but, of the five species, only in Taonius sp. B (Voss) did these indices correlate with, δ13C and δ15N values, indicating direct relationships between environmental conditions, habitat and trophic level. The five cephalopod species therefore changed their habitats with changing environmental conditions over the last 50 years but maintained similar trophic levels. Hence, cephalopods are likely to remain important prey for top predators in Southern Ocean food webs, despite ongoing climate change.

New bobtail squid (Sepiolidae: Sepiolinae) from the Ryukyu islands revealed by molecular and morphological analysis.

Bobtail squid are emerging models for host-microbe interactions, behavior, and development, yet their species diversity and distribution remain poorly characterized. Here, we combine mitochondrial and transcriptome sequences with morphological analysis to describe three species of bobtail squid (Sepiolidae: Sepiolinae) from the Ryukyu archipelago, and compare them with related taxa. One Ryukyuan type was previously unknown, and is described here as Euprymna brenneri sp. nov. Another Ryukyuan type is morphologically indistinguishable from Sepiola parva Sasaki, 1913. Molecular analyses, however, place this taxon within the genus Euprymna Steenstrup, 1887, and additional morphological investigation led to formal rediagnosis of Euprymna and reassignment of this species as Euprymna parva comb. nov. While no adults from the third Ryukyuan type were found, sequences from hatchlings suggest a close relationship with E. pardalota Reid, 2011, known from Australia and East Timor. The broadly sampled transcriptomes reported here provide a foundation for future phylogenetic and comparative studies.