Systematics and Distributions of Upper Bathyal Species in Bathyancistrolepis, a Deep-Sea Whelk Genus Endemic to the Northwest Pacific (Gastropoda: Buccinidae).

The deep-sea buccinid snail genus Bathyancistrolepis is redefined based on the reconstruction of a molecular phylogeny and morphological examination of shell and radular characters. This genus is distinguished from other genera of the subfamily Parancistrolepidinae with a combination of shell traits, including (1) a low spire, (2) sharp, carinate spiral cords or keels and (3) a long, curved siphonal canal, but not with a difference in radular morphology as suggested by previous authors. Three allopatric or parapatric species are recognized in the upper bathyal (447-2057 m) waters around Japan and Taiwan: B. tokoyodaensis from off Hokkaido to Sagami Bay in the Northwest Pacific, B. trochoidea off Kumano-nada to Miyazaki in the Northwest Pacific and along Nansei Islands in the East China Sea, and B. taiwanensis sp. nov. in the South China Sea. These species bear large paucispiral protoconchs that are indicative of benthic early development without a pelagic larval period, and hence low dispersal capability. Seafloor topography seems to have acted as a barrier for their dispersal; the range of B. tokoyodaensis supports the previous finding that Izu Peninsula delimits westward distribution of bathyal gastropod species of boreal origins.

Fusceulimoides kohtsukai gen. et sp. nov., a Minute Eulimid Gastropod Parasitic on the Little Brittle Star Ophiactis savignyi in Central Japan.

Gastropods of over a dozen genera in the family Eulimidae have been identified as parasites of brittle stars, and many more remain to be discovered and described for a comprehensive understanding of the evolutionary history of their host-parasite relationships. In this study, we describe Fusceulimoides kohtsukai gen. et sp. nov., parasitic on the little brittle star, Ophiactis savignyi (Ophiactidae), in Kanagawa, central Japan. The new genus is distinguished from other eulimid genera by the combination of following seven conchological characters: (1) a very small size of up to 1.7 mm high, (2) a colorless translucent appearance, (3) a conical pupiform shape with a paucispiral protoconch, (4) slightly convex teleoconch whorls, (5) a remarkably large body whorl occupying 65-70% of the total shell height, (6) a broad, somewhat squarish and laterally expanded aperture with a strongly curved outer lip, and (7) a developed parietal callus without an indentation or depression in the umbilical area. A multi-locus molecular phylogeny revealed its distant relationship to Hemiliostraca + Pyramidelloides, a previously known clade of ophiuroid parasites, thereby suggesting multiple origins of this host-parasite association in Eulimidae.

A Phylogenomic Backbone for Gastropod Molluscs.

Gastropods have survived several mass extinctions during their evolutionary history resulting in extraordinary diversity in morphology, ecology, and developmental modes, which complicate the reconstruction of a robust phylogeny. Currently, gastropods are divided into six subclasses: Caenogastropoda, Heterobranchia, Neomphaliones, Neritimorpha, Patellogastropoda, and Vetigastropoda. Phylogenetic relationships among these taxa historically lack consensus, despite numerous efforts using morphological and molecular information. We generated sequence data for transcriptomes derived from 12 taxa belonging to clades with little or no prior representation in previous studies in order to infer the deeper cladogenetic events within Gastropoda and, for the first time, infer the position of the deep-sea Neomphaliones using a phylogenomic approach. We explored the impact of missing data, homoplasy, and compositional heterogeneity on the inferred phylogenetic hypotheses. We recovered a highly supported backbone for gastropod relationships that is congruent with morphological and mitogenomic evidence, in which Patellogastropoda, true limpets, are the sister lineage to all other gastropods (Orthogastropoda) which are divided into two main clades 1) Vetigastropoda $s.l.$ (including Pleurotomariida $+$ Neomphaliones) and 2) Neritimorpha $+$ (Caenogastropoda $+$ Heterobranchia). As such, our results support the recognition of five subclasses (or infraclasses) in Gastropoda: Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda, and Heterobranchia. [Compositional heterogeneity; fast-evolving; long-branch attraction; missing data; Mollusca; phylogenetics; systematic error.].

A global phylogeny of the deep-sea gastropod family Scaphandridae (Heterobranchia: Cephalaspidea): Redefinition and generic classification.

We present the most comprehensive phylogeny of a globally distributed deep-sea group of gastropods published to date including over 80% of the recognized diversity of the family Scaphandridae. The definition and taxonomic composition of the Scaphandridae has been hampered by the lack of a sound phylogenetic framework and definition of synapomorphic traits. We used a combination of molecular phylogenetics (Bayesian Inference and Maximum Likelihood) based on five gene markers (cytochrome c oxidase subunit I, 12S rRNA, 16S rRNA, 18S rRNA, and 28S rRNA) and morpho-anatomical characters to redefine the Scaphandridae and its genera. A new classification is proposed with the three genera Nipponoscaphander, Sabatia, and Scaphander. Main differences between genera lie on the shells (shape, parietal callus, spire) and male reproductive system (prostate). The species Hamineobulla kawamurai is reassigned to the closely related family Eoscaphandridae, currently defined mostly based on pleisiomorphic traits. Biogeographically the genus Nipponoscaphander is restricted to the Indo-West Pacific; Sabatia is mostly circumscribed to the Indo-West Pacific, but has one lineage present in the north Atlantic Ocean. Polyphyly across ocean realms prevails in the specious and globally distributed genus Scaphander with multiple speciation events between Indo-Pacific and Atlantic lineages but also with several episodes of cladogenesis within realms. Two rare cases of species with a broad distribution spanning the Indo-West Pacific and Atlantic realms are confirmed (S. meridionalis and S. nobilis).

Origin and significance of two pairs of head tentacles in the radiation of euthyneuran sea slugs and land snails.

The gastropod infraclass Euthyneura comprises at least 30,000 species of snails and slugs, including nudibranch sea slugs, sea hares and garden snails, that flourish in various environments on earth. A unique morphological feature of Euthyneura is the presence of two pairs of sensory head tentacles with different shapes and functions: the anterior labial tentacles and the posterior rhinophores or eyestalks. Here we combine molecular phylogenetic and microanatomical evidence that suggests the two pairs of head tentacles have originated by splitting of the original single tentacle pair (with two parallel nerve cords in each tentacle) as seen in many other gastropods. Minute deep-sea snails of Tjaernoeia and Parvaplustrum, which in our phylogeny belonged to the euthyneurans' sister group (new infraclass Mesoneura), have tentacles that are split along much of their lengths but associated nerves and epidermal sense organs are not as specialized as in Euthyneura. We suggest that further elaboration of cephalic sense organs in Euthyneura closely coincided with their ecological radiation and drastic modification of body plans. The monotypic family Parvaplustridae nov., superfamily Tjaernoeioidea nov. (Tjaernoeiidae + Parvaplustridae), and new major clade Tetratentaculata nov. (Mesoneura nov. + Euthyneura) are also proposed based on their phylogenetic relationships and shared morphological traits.

First Complete Mitochondrial Genome of a Tanaidacean Crustacean (Arctotanais alascensis).

We present a complete mitochondrial genomic sequence for the tanaidacean Arctotanais alascensis (Richardson, 1899); this is the first complete mitogenome reported from the order Tanaidacea. The mitogenome is 13,988 bp long and contains 13 protein coding and two ribosomal RNA genes (as is typical for animal mitogenomes), and 21 of 22 transfer RNAs; we did not detect an isoleucine transfer RNA (trnI) gene. The gene order differed markedly from the hypothetical ground pattern for Pancrustacea; only four clusters (trnM + nad2; trnC + trnY + cox1 + trnL2 + cox2; trnD + atp8 + atp6 + cox3; trnH + nad4 + nad4l) ancestrally present were retained. In a malacostracan phylogenetic tree reconstructed from mitogenome data, basal relationships were marginally supported or incongruent with the traditional morphology-based classification and the latest phylogenetic reconstructions from large transcriptomic datasets. Relationships involving more recent divergences were better supported in our tree, suggesting that complete mitogenome sequences are more suitable for phylogenetic analyses within malacostracan orders, presumably including Tanaidacea.

Snails riding mantis shrimps: Ectoparasites evolved from ancestors living as commensals on the host's burrow wall.

The molluscan class Gastropoda includes over 5,000 parasitic species whose evolutionary origins remain poorly understood. Marine snails of the genus Caledoniella (Caledoniellidae) are obligate parasites that live on the abdominal surface of the gonodactylid mantis shrimps. They have highly modified morphological characteristics specialized to the ectoparasitic lifestyle that make it difficult to infer their close relatives, thereby posing a question about their current systematic position in the superfamily Vanikoroidea. In the present study, we performed molecular phylogenetic analyses using three nuclear and three mitochondrial gene sequences to unveil the phylogenetic position of these enigmatic snails. The resulting trees recovered Caledoniella in the superfamily Truncatelloidea and within a subclade of commensal species that live on the burrow wall of marine benthic invertebrates. More specifically, Caledoniella formed the sister clade to a commensal snail species living in mantis-shrimp burrows and they collectively were sister to Sigaretornus planus (formerly in the family Tornidae or Vitrinellidae), a commensal living in echiuran burrows. This topology suggests that the species of Caledoniella achieved their ectoparasitic mode of life through the following evolutionary pathway: (1) invasion into the burrows of benthic invertebrates, (2) specialization to mantis shrimps, and (3) colonization of the host body surface from the host burrow wall with the evolution of the parasitic nature. The final step is likely to have been accompanied by the acquisition of a sucker on the metapodium, the loss of the radula and operculum, and the formation of monogamous pair bonds. The present molecular phylogeny also suggested parallel evolution of planispiral shells in a subclade of Truncatelloidea and enabled us to newly redefine the families Caledoniellidae, Elachisinidae, Teinostomatidae, Tornidae and Vitrinellidae.

Eight new mitogenomes clarify the phylogenetic relationships of Stromboidea within the caenogastropod phylogenetic framework.

Members of the gastropod superfamily Stromboidea (Littorinimorpha) are characterised by their elaborate shell morphologies, distinctive mode of locomotion, and often large and colourful eyes. This iconic group comprises over 130 species, including many large and charismatic species. The family Strombidae is of particular interest, largely due to its commercial importance and wide distribution in tropical and subtropical waters. Although a few strombid mitochondrial genomes have been sequenced, data for the other four Recent families in Stromboidea are lacking. In this study we report seven new stromboid mitogenomes obtained from transcriptomic and genomic data, with taxonomic representation from each Recent stromboid family, including the first mitogenomes for Aporrhaidae, Rostellariidae, Seraphsidae and Struthiolariidae. We also report a new mitogenome for the family Xenophoridae. We use these data, along with published sequences, to investigate the relationships among these and other caenogastropod groups. All analyses undertaken in this study support monophyly of Stromboidea as redefined here to include Xenophoridae, a finding consistent with morphological and behavioural data. Consistent with previous morphological and molecular analyses, including those based on mitogenomes, monophyly of Hypsogastropoda is confirmed but monophyly of Littorinimorpha is again rejected.

The mitochondrial genome and phylogenetic position of a marine snail Nerita (Heminerita) japonica (Gastropoda: Neritimorpha: Neritidae).

The mitochondrial genome of the neritid snail Nerita (Heminerita) japonica (Mollusca: Neritimorpha) from Kumamoto, Japan was determined by whole-genome sequencing. This mitogenome is comprised of 13 protein-coding genes, 2 ribosomal RNA (12S and 16S) genes, and 22 transfer RNA genes, with the same gene order as in the other species of the family Neritidae. A likelihood-based phylogenetic reconstruction recovered the subgenus Heminerita (including N. japonica as its type and N. yoldii from China) as monophyletic and sister to a clade with four species of the subgenera Nerita and Theliostyla.

Population connectivity of the hydrothermal-vent limpet Shinkailepas tollmanni in the Southwest Pacific (Gastropoda: Neritimorpha: Phenacolepadidae).

The Southwest Pacific represents an independent biogeographic province for deep-sea hydrothermal vent fauna. Different degrees of genetic connectivity among vent fields in Manus, North Fiji and Lau Basins have been reported for various molluscan and crustacean species, presumably reflecting their different levels of dispersal ability as swimming larvae. The present study investigates the population connectivity of the hydrothermal vent limpet Shinkailepas tollmanni (family Phenacolepadidae) in the Southwest Pacific. Our analyses using mitochondrial COI-gene sequences and shell morphometric traits suggest a panmictic population structure throughout its geographic and bathymetric ranges, spanning 4,000 km from the westernmost Manus Basin (151ºE; 1,300 m deep) to the easternmost Lau Basin (176ºE; 2,720 m). The measurements of its embryonic and larval shells demonstrate that the species hatches as a planktotrophic veliger larva with an embryonic shell diameter of 170-180 µm and settles at the vent environment with the larval shell diameter of 750-770 µm. This substantial growth as a feeding larva, ca. 80 times in volume, is comparable or even greater than those of confamilial species in the hydrothermal-vent and methane-seep environments in the Northwest Pacific and Atlantic Oceans. Large pigmented eyes in newly settled juveniles are another common feature in this and other phenacolepadids inhabiting the chemosynthetic environments. These results put together suggest that the larvae of S. tollmanni migrate vertically from deep-sea vents to surface waters to take advantages of richer food supplies and faster currents and stay pelagic for an extended period of time (> 1 year), as previously indicated for the confamilial species.

Host identification for the deep-sea snail genus Haliella with description of a new species (Caenogastropoda, Eulimidae).

A new parasitic species of eulimid gastropod, Haliella seisuimaruae sp. nov., is described from bathyal (728-978 m) waters off the Pacific coasts of Japan. It shows the closest resemblance to the type species H. stenostoma from the North Atlantic and Barents Sea in having a tall shell with an almost straight outer lip, but differs in having a junction of the parietal wall and columellar lip at 38% of the aperture height from the suture (33% in H. stenostoma), a slightly wider aperture and a more curved and extended columellar lip. The holotype of H. seisuimaruae sp. nov. was found attached to an irregular sea urchin, Brissopsis sp. cf. luzonica (Spatangoida: Brissidae). This represents the first direct observation of parasitic ecology and echinoderm host for the genus Haliella. A new replacement name, Eulima tsushimensis nom. nov., is proposed here for Eulima stenostoma A. Adams, 1861, which is preoccupied by Eulima stenostoma Jeffreys, 1858 (type of Haliella).

Putting keyhole limpets on the map: phylogeny and biogeography of the globally distributed marine family Fissurellidae (Vetigastropoda, Mollusca).

Fissurellidae are marine gastropods with a worldwide distribution and a rich fossil record. We integrate molecular, geographical and fossil data to reconstruct the fissurellid phylogeny, estimate divergence times and investigate historical routes of oceanic dispersal. With five molecular markers for 143 terminals representing 27 genera, we resolve deep nodes and find that many genera (e.g., Emarginula, Diodora, Fissurella) are not monophyletic and need systematic revision. Several genera classified as Emarginulinae are recovered in Zeidorinae. Future work should prioritize emarginuline genera to improve understanding of ancestral traits and the early evolution of fissurellids. Tree calibration with the fossilized birth-death model indicates that crown fissurellids originated around 175 Ma, and generally resulted in younger ages for the earliest nodes than the node dating approach. Model-based biogeographic reconstruction, supported by fossils, infers an Indo-West Pacific origin, with a westward colonization of new oceans via the Tethys Seaway upon the breakup of Pangea. Western Atlantic clades then served as source for dispersal towards other parts of the globe. As the sister group to all other fissurellids, Rimula is ranked in its own subfamily, Rimulinae stat. nov. New synonyms: Hemitominae syn. nov. of Zeidorinae stat. nov.; Cranopsissyn. nov. of Puncturella; Variegemarginulasyn. nov. of Montfortula.

Megadenus atrae n. sp., an endoparasitic eulimid gastropod (Mollusca) from the black sea cucumber Holothuria atra Jaeger (Aspidochirotida: Holothuriidae) in the Indo-West Pacific.

An eulimid gastropod, Megadenus atrae n. sp., endoparasitic in the cloacal chamber of the black sea cucumber Holothuria atra Jaeger is described from Okinawa, Japan, as the fifth species of the genus. Conspecific specimens have also been found from southeast India, northeast Australia and New Caledonia. The generic assignment is justified by the presence of (i) a thick, long proboscis that bears a large fold (pseudopallium) near the base and a collar-like structure at the middle, (ii) a thin, globose shell that is covered by the pseudopallium, and (iii) sexual dimorphism with the female generally larger than the male. The new species is distinguishable from the four previously described congeners by its cauldron-shaped pseudopallium, moderately-developed collar of the proboscis and rounded basal lip of the shell. The comparisons of the size and sex of solitary and paired individuals support a previous hypothesis that the species of Megadenus Rosén, 1910 are protandrous with environmental sex determination. The present species occurs mostly as monogamous pairs despite its very low population density, implying that the presence of a conspecific individual acts as a cue for larval settlement. Both mechanisms would increase individual reproductive success in such permanent parasites with low prevalence and abundance as the species of Megadenus.

Do larvae from deep-sea hydrothermal vents disperse in surface waters?

Larval dispersal significantly contributes to the geographic distribution, population dynamics, and evolutionary processes of animals endemic to deep-sea hydrothermal vents. Little is known as to the extent that their larvae migrate vertically to shallower waters and experience stronger currents and richer food supplies. Here, we first provide evidence from early life-history traits and population genetics for the surface dispersal of a vent species. Planktotrophic larvae of a red blood limpet, Shinkailepas myojinensis (Gastropoda: Neritimorpha: Phenacolepadidae), were cultured to observe their swimming behavior and to evaluate the effects of temperature on survival and growth. In addition, the population structure was analyzed based on 1.2-kbp mitochondrial DNA sequences from 77 specimens that cover the geographic and bathymetric distributions of the species (northwest Pacific, 442-1,227 m in depth). Hatched larvae constantly swam upward at 16.6-44.2 mm/min depending on temperature. Vertical migration from hydrothermal vents to the surface, calculated to take ~4-43 d, is attainable given their lengthy survival time without feeding. Fed larvae best survived and grew at 25°C (followed by 20°C), which approximates the sea surface temperature in the geographic range of the species. Little or no growth was observed at the temperature of the vent habitat where adult limpets occur (≤15°C). Population genetic analyses showed no differentiation among localities that are <1,350 km apart. The larvae of S. myojinensis most likely migrate to the surface water, where high phytoplankton biomass and strong currents enable their growth and long distance dispersal over many months. Sea surface temperature may represent a critical factor in determining the geographic distribution of many vent endemic species with a planktotrophic early development, and in turn the faunal composition of individual vent sites and regions.

Ringiculid bubble snails recovered as the sister group to sea slugs (Nudipleura).

Euthyneuran gastropods represent one of the most diverse lineages in Mollusca (with over 30,000 species), play significant ecological roles in aquatic and terrestrial environments and affect many aspects of human life. However, our understanding of their evolutionary relationships remains incomplete due to missing data for key phylogenetic lineages. The present study integrates such a neglected, ancient snail family Ringiculidae into a molecular systematics of Euthyneura for the first time, and is supplemented by the first microanatomical data. Surprisingly, both molecular and morphological features present compelling evidence for the common ancestry of ringiculid snails with the highly dissimilar Nudipleura-the most species-rich and well-known taxon of sea slugs (nudibranchs and pleurobranchoids). A new taxon name Ringipleura is proposed here for these long-lost sisters, as one of three major euthyneuran clades with late Palaeozoic origins, along with Acteonacea (Acteonoidea + Rissoelloidea) and Tectipleura (Euopisthobranchia + Panpulmonata). The early Euthyneura are suggested to be at least temporary burrowers with a characteristic 'bubble' shell, hypertrophied foot and headshield as exemplified by many extant subtaxa with an infaunal mode of life, while the expansion of the mantle might have triggered the explosive Mesozoic radiation of the clade into diverse ecological niches.

Phylogenetic relationships among superfamilies of Neritimorpha (Mollusca: Gastropoda).

Despite the extraordinary morphological and ecological diversity of Neritimorpha, few studies have focused on the phylogenetic relationships of this lineage of gastropods, which includes four extant superfamilies: Neritopsoidea, Hydrocenoidea, Helicinoidea, and Neritoidea. Here, the nucleotide sequences of the complete mitochondrial genomes of Georissa bangueyensis (Hydrocenoidea), Neritina usnea (Neritoidea), and Pleuropoma jana (Helicinoidea) and the nearly complete mt genomes of Titiscania sp. (Neritopsoidea) and Theodoxus fluviatilis (Neritoidea) were determined. Phylogenetic reconstructions using probabilistic methods were based on mitochondrial (13 protein coding genes and two ribosomal rRNA genes), nuclear (partial 28S rRNA, 18S rRNA, actin, and histone H3 genes) and combined sequence data sets. All phylogenetic analyses except one converged on a single, highly supported tree in which Neritopsoidea was recovered as the sister group of a clade including Helicinoidea as the sister group of Hydrocenoidea and Neritoidea. This topology agrees with the fossil record and supports at least three independent invasions of land by neritimorph snails. The mitochondrial genomes of Titiscania sp., G. bangueyensis, N. usnea, and T. fluviatilis share the same gene organization previously described for Nerita mt genomes whereas that of P. jana has undergone major rearrangements. We sequenced about half of the mitochondrial genome of another species of Helicinoidea, Viana regina, and confirmed that this species shares the highly derived gene order of P. jana.

Molecular phylogeny of the Ellobiidae (Gastropoda: Panpulmonata) supports independent terrestrial invasions.

Gastropods of the family Ellobiidae are an interesting group in which to study transitions from intertidal to terrestrial realms. However, the phylogenetic relationships within this family still lack resolution. We present a phylogenetic hypothesis of the Ellobiidae based on Bayesian and maximum likelihood phylograms. We used nuclear (18S, 28S, H3) and mitochondrial (16S, 12S, COI) data, increasing the numbers of markers and data, and making this the most comprehensive phylogenetic study of the family to date. Our results support phylogenetic hypotheses derived from morphological data, and provide a supported framework to evaluate the internal relationships within Ellobiidae. The resulting phylogenetic trees support the previous hypothesis that the Ellobiidae are monophyletic only if the Trimusculinae (Otina, Smeagol and Trimusculus) are considered part of this family. In addition, we found that the Carychiinae, Ellobiinae and Pythiinae are reciprocally monophyletic and closely related, with the Carychiinae as sister group to Ellobiinae. Relationships within Melampodinae and Pedipedinae and their phylogenetic positions remain unresolved. Land invasion by the Ellobiidae occurred independently in Carychiinae and Pythia during different geological times (Mesozoic and Cenozoic, respectively). Diversification in the family does not appear to be related to past climate and biotic changes, neither the Cretaceous-Paleogene boundary nor the lowering of the sea level in the Oligocene.

The complete mitochondrial genome of the stream snail Clithon retropictus (Neritimorpha: Neritidae).

The complete mitochondrial genome of the stream neritid Clithon retropictus was determined by next-generation sequencing. The mitochondrial genome is 15,814 bp in length, comprising two ribosomal RNA genes, 13 protein-coding genes (PCGs) and 22 transfer RNA genes (tRNAs). Of these 37 genes identified, 7 PCGs and 8 tRNAs are encoded on the heavy strand and the other genes on the light strand. This gene order is consistent with the previously published mitochondrial genomes of the other neritid species. This is the first report of a complete mitochondrial genome sequence for the genus and the fourth for the gastropod subclass Neritimorpha.

Morphological and Genetic Variation Between the Japanese Populations of the Amphidromous Snail Stenomelania crenulata (Cerithioidea: Thiaridae).

Freshwater gastropods often have limited dispersal capability and small geographic ranges, and face severe threats from habitat loss and degradation. However, in addition to the scarcity of knowledge on their life history traits, species taxonomy has not been adequately resolved and boundaries between intra- and interspecific variation remain unclear for many taxa. One such example of an indeterminate species boundary with implications for conservation issues is the relationship between the thiarid snails Stenomelania crenulata in Okinawa and southwards (ranked as CR+EN in the 2012 Japanese Red List) and S. rufescens in mainland Japan (VU). The results of our multi-disciplinary investigation into variation in the shell morphology and mitochondrial (COI) and nuclear (ITS-1) gene sequences suggest that S. rufescens represents a geographic variant and a junior synonym of S. crenulata. The widespread geographic range of S. crenulata, spanning a few thousand kilometers north to south, is possible due to an amphidromous life cycle that involves a marine planktotrophic larval phase and upstream migration after settlement in estuaries. Nevertheless, there is recognizable morphological and genetic differentiation between distant populations, probably reflecting a relatively short pelagic duration and possibly also infrequent transoceanic dispersal; metamorphic competence is achieved in two weeks in full seawater and even more rapidly in brackish water. The Okinawan population, with only a few known localities, therefore deserves the high conservation priority; conservation efforts need to involve the proper maintenance of migration pathways including all marine, brackish and freshwater environments.