Ontogenetic Changes in Pigmentation Pattern in Mesanthura miyakoensis (Crustacea: Isopoda: Anthuridae).

Species in the anthurid isopod genus Mesanthura have specific, dorsal dark pigmentation patterning on the body. Though Mesanthura species have traditionally been distinguished mainly by differences in the dorsal pigmentation pattern in females, the stability of the pigmentation pattern within species had not been investigated, and information was lacking on ontogenetic variation in the pattern. Our study showed the following for M. miyakoensis. (1) Mancae begin to show dorsal pigmentation in the marsupium roughly 9 days before their release. (2) The pigmentation pattern in the first-instar mancae (first free-living stage) differs from that in later instars. (3) The pigmentation pattern in females is discrete and stable from putative second-instar mancae through females lacking oostegites, and distorted but recognizable in ovigerious females. (4) The pattern in males is different from and less discrete than that in females; it remains similar through the molt from subadult to adult male but changes markedly with age, leading to heavy pigmentation of the body. (5) The pigmentation pattern in mancae and females remains stable and observable after storage in ethanol for at least 13.7 months. Our results suggest that comparisons of pigmentation pattern across species in Mesanthura taxonomy should be restricted to females in the post-manca or later stages.

Flatworm cocoons in the abyss: same plan under pressure.

While knowledge of early ontogeny in abyssal animals is highly limited in general, it was completely lacking for abyssal, free-living platyhelminths. We discovered flatworm egg capsules (or 'cocoons') on rocks collected at depths of 6176-6200 m on the abyssal slope of the Kuril-Kamchatka Trench, northwestern Pacific. The egg capsules were black and spherical, around 3 mm in diameter, and contained three to seven individuals (n = 4) at the same developmental stage, either the spherical (putative early embryo) or vermiform (putative late embryo) stages. A molecular phylogenetic analysis based on 18S and 28S rRNA sequences revealed that the flatworms belong in suborder Maricola in Tricladida and suggested that they may have colonized from shallow to deep waters. This study provides the deepest record for free-living flatworms and the first information on their early life stages in the abyssal zone, which were very similar to those in shallow-water forms. This similarity in development between the relatively benign shallow-water and the extreme abyssal environments suggests that triclads adapting to the latter faced primarily physiological and/or ecological adaptive challenges rather than developmental ones.

Phototaxis in Two Shallow-Water Zeuxo Species (Crustacea: Tanaidacea).

Different crustacean species can differ in their response to light. In Tanaidacea, a small group of aquatic, benthic crustaceans, previous studies suggested that several species may be positively phototactic based on their attraction to nocturnal light traps, but no experimental investigations of phototaxis had been conducted on this group. Here we show experimentally that two species in the genus Zeuxo are phototactic but exhibit opposite reactions to light; Zeuxo ezoensis, which inhabits the blades and stipes of seaweeds, was positively phototactic, whereas Zeuxo molybi, which inhabits muddy sediments overlying bedrock, was negatively phototactic. This differential response may reflect differences in photoenvironment between these species' microhabitats.

Diexanthema hakuhomaruae sp. nov. (Copepoda: Siphonostomatoida: Nicothoidae) from the Hadal Zone in the Northwestern Pacific, with an 18S Molecular Phylogeny.

PURPOSE: Diexanthema copepods are ectoparasites on deep-sea isopods. This genus currently contains six species, all reported from the North Atlantic. Our study describes a new species of Diexanthema found on isopods from 7184 to 7186 m depth in the Kuril-Kamchatka Trench, northwestern Pacific. METHODS: We observed the copepod's morphology, made camera-lucida drawings, and compared our species with congeners. We determined partial sequences for its 16S rRNA and 18S rRNA genes and constructed an 18S-based maximum-likelihood copepod tree to place it phylogenetically. We identified the host isopod species through morphology and cytochrome c oxidase subunit I (COI, cox1) and 18S sequences. RESULTS/CONCLUSION: We described the copepod as Diexanthema hakuhomaruae sp. nov. and identified its host as Eugerdella cf. kurabyssalis Golovan, 2015 (Desmosomatidae). This is the first Diexanthema copepod from the Pacific and also from hadal depths. Diexanthema hakuhomaruae most closely resembles D. bathydiaita Richie, 1975, parasitic on Nannoniscus sp. (Nannoniscidae) in the Atlantic, but differs from the latter in having a smooth body surface and leg 5 in the ventrolateral region of the urosome. In the 18S tree, D. hakuhomaruae was the sister group to the Rhizorhina clade, which is consistent with the morphology-based hypothesis that they are closely related.

A new Sphaeronella species (Copepoda: Siphonostomatoida: Nicothoidae) parasitic on Euphilomedes sp. (Ostracoda: Myodocopa: Philomedidae) from Hokkaido, Japan, with an 18S molecular phylogeny.

With about 80 species, Sphaeronella is the most species-rich genus in the copepod family Nicothoidae. To date, 20 named Sphaeronella species have been reported as ectoparasites on ostracod crustaceans. Here we describe Sphaeronella uyenoi sp. nov. parasitic on the philomedid ostracod Euphilomedes sp. collected from Akkeshi Bay, Hokkaido, Japan, northwestern Pacific. Sphaeronella uyenoi most closely resembles S. monothrix (Bowman & Kornicker, 1967), parasitic on the cylindroleberidid Parasterope pollex Kornicker in Bowman & Kornicker in the northwestern Atlantic, but differs from the latter in having (1) the submedian skeleton containing paired, strongly chitinized, Λ-shaped areas and paired wide oblong holes bearing a strongly chitinized fringe posteriorly, and (2) maxillipedal segment 3 with antero-subdistal serration. We determined partial sequences for the cytochrome c oxidase subunit I (COI) and 18S rRNA (18S) genes for S. uyenoi and constructed an 18S-based phylogenetic tree of copepods. In our tree, Nicothoidae was not monophyletic, and S. uyenoi was the sister taxon to Cancerilla sp. in Cancerillidae (ectoparasites on brittle stars).

Capropodocerus, a new genus in Podoceridae (Crustacea: Amphipoda) from Japan, with descriptions of two new species.

We establish the new podocerid genus Capropodocerus gen. nov. for the two new species Capropodocerus tagamaru gen. et sp. nov. (collected from 775800 m depth in the Kumano Sea, Japan) and Capropodocerus kamaitachi gen. et sp. nov. (collected from 840873 m depth off the eastern coast of Miyagi, Japan). Capropodocerus shares elongate pereonites 13 with Neoxenodice but differs from the latter in lacking uropod 2 and in having pereonite 3 at least twice as long as pereonite 4. Capropodocerus is also similar to Laetmatophilus and Leipsuropus in having only two pairs of uropods but differs from them in having i) pereonite 1 longer than the head and ii) pereonite 3 at least twice as long as pereonite 4; Capropodocerus has three urosomes and Laetmatophilus has two urosomes. The two species in Capropodocerus differ in i) the length ratio of the antenna 1 peduncle to the flagellum, ii) the shape of the gnathopod 2 palm, iii) the presence or absence of a mid-posterior triangular projection on the gnathopod 2 dactylus, and iv) the length ratio of the basis to the merus of pereopod 3. A key to all genera in Podoceridae is provided.

Observations on Predation in Paranthura japonica Richardson, 1909 (Isopoda: Cymothoida: Paranthuridae).

Although isopods in Anthuroidea are predators, there is little information on their predatory behavior. In this study, we investigated predation by the paranthurid Paranthura japonica, which was originally described from northern Japan but has recently been reported as an invasive alien species in western America and Europe. Six crustacean species (two isopods, two amphipods, and two tanaidaceans, one of which does not co-occur with P. japonica in the wild) and one pycnogonid species were used as prey candidates in our experiments. Paranthura japonica preyed on all candidate species except the pycnogonid, grasping them with its falciform pereopods, inserting its piercing-type mouthparts, and sucking out the internal contents of the prey. Cannibalism or scavenging was observed when several P. japonica individuals were put in a single aquarium. This study showed that P. japonica is an aggressive predator; it consumed various crustaceans, including one it never encounters in the wild. Our results suggest that P. japonica will have a high impact on alien ecosystems it invades as a predator on native crustaceans. Cytochrome c oxidase subunit (COI) nucleotide sequences for putative P. japonica from Oshoro, Japan and a topotypic individual from Muroran confirmed that the population we dealt with was P. japonica.

Digenean Metacercariae Parasitic in a Staurozoan Cnidarian.

I report digenean metacercariae from Staurozoa, which were not previously known as digenean hosts. The host species, Haliclystus tenuis Kishinouye, 1910, was collected from algae in Oshoro Bay, Hokkaido, Japan, and contained metacercariae in the mesoglea. The metacercariae were encysted; cysts were oval, 93 µm long by 64 µm wide in one live individual. For the digenean, I generated partial sequences for the 18S rRNA (1585 bp) and 28S rRNA (1672 bp) genes, and the region spanning the 3' end of the cytochrome c oxidase subunit gene and the 5' end of the 16S rRNA gene, including the threonine tRNA gene (868 bp in total). Phylogenetic reconstructions based on combined 18S + 28S datasets showed the digenean to belong in Opecoelidae, members of which utilize marine or freshwater teleost fishes as definitive hosts, and placed it in Plagioporinae (sensu lato) clade C within Opecoelidae.

Three Free-Living Marine Nematodes from Sagami Bay, Japan, with a Description of Wiesoncholaimus jambio sp. nov. (Nematoda: Oncholaimidae).

We describe three free-living marine nematode species from Sagami Bay, Japan. Wiesoncholaimus jambiosp. nov. is the second species of this genus. It differs from the type species, Wiesoncholaimus mawsonae Inglis, 1966, by its dorsal tooth, which is as long as the other two teeth; its conico-cylindrical tail, which is as long as 4.6-4.8 cloacal body diameters; and the absence of the gubernaculum. Thalassironus cf. britannicus de Man, 1889 agrees well with a redescription of Thalassironus britannicus de Man, 1889 based on specimens collected near the type locality. However, as it is possible that T. britannicus sensu lato includes two or more species, our species may not be conspecific to T. britannicus sensu stricto. Vasostoma cf. longispicula Huang and Wu, 2010 closely resembles Vasostoma longispicula Huang and Wu, 2010 originally described from China, but minor differentiations are observed in body diameter, body cuticle thickness, and type of precloacal supplements.

Description of a New Hamatipeda Species, with an 18S Molecular Phylogeny (Crustacea: Tanaidacea: Typhlotanaidae).

We describe a new typhlotanaid species, Hamatipeda kohtsukai sp. nov., collected from between 167 and 488 m depth in the Sagami Sea, Japan. This is the first record of Hamatipeda from the northern hemisphere. Hamatipeda kohtsukai resembles Hamatipeda trapezoida from the Subantarctic region in having pereonites 1-3 widest anteriorly (not rectangular), but differs from it in the length ratio of antennal articles 4/5; the number of setae on the dactyli of pereopods 1-3, ischia of pereopods 4-6, and carpi of pereopods 4-6; the shape of the unguis of pereopods 4-6; and the shape of the uropodal endopod. We determined partial sequences for the cytochrome c oxidase subunit I (COI; cox1) and 18S rRNA (18S) genes in H. kohtsukai. A phylogenetic reconstruction based on the 18S sequences recovered a highly supported Typhlotanaidae clade containing H. kohtsukai and Typhlotanais mixtus, with Paranarthrura sp. (Agathotanaidae) as the sister taxon. A key to species of Hamatipeda is presented.

Comprehensive Transcriptome Sequencing of Tanaidacea with Proteomic Evidences for Their Silk.

Tanaidaceans are small benthic crustaceans that mainly inhabit diverse marine environments, and they comprise one of the most diverse and abundant macrofaunal groups in the deep sea. Tanaidacea is one of the most thread-dependent taxa in the Crustacea, constructing tubes, spun with their silk, for shelter. In this work, we sequenced and assembled the comprehensive transcriptome of 23 tanaidaceans encompassing 14 families and 4 superfamilies of Tanaidacea, and performed silk proteomics of Zeuxo ezoensis to search for its silk genes. As a result, we identified two families of silk proteins that are conserved across the four superfamilies. The long and repetitive nature of these silk genes resembles that of other silk-producing organisms, and the two families of proteins are similar in composition to silkworm and caddisworm fibroins, respectively. Moreover, the amino acid composition of the repetitive motifs of tanaidacean silk tends to be more hydrophilic, and therefore could be a useful resource in studying their unique adaptation of silk use in a marine environment. The availability of comprehensive transcriptome data in these taxa, coupled with proteomic evidence of their silk genes, will facilitate evolutionary and ecological studies.

A new species of Expanathura (Crustacea: Isopoda: Anthuroidea) from Iriomote Island, Japan, with a note on male polymorphism.

We describe Expanathura monile sp. nov. from Iriomote Island, Okinawa, Japan, northwestern Pacific. This species resembles E. collaris, E. macronesia, and E. haddae in having very broad uropodal rami, a broad telson, and a moderately shortened pleopod 1 endopod, but differs from these three species in the female having (1) the head with a dorsal V-shaped band of brown pigmentation, (2) the antennular flagellum with 34 articles, (3) antennal peduncular article 2 with an outer triangular projection, (4) the uropodal endopod longer than wide, (5) the uropodal exopod with an acute triangular projection, (6) an oval telson, and (7) the posterolateral setae on the telson similar in length. We present a revised key to known species in the genus Expanathura and briefly discuss the male polymorphism observed in E. monile.

First report of marine horsehair worms (Nematomorpha: Nectonema) parasitic in isopod crustaceans.

Nectonema, the only horsehair worm (Nematomorpha) genus found in marine environments, was previously known to be parasitic only in decapod crustaceans. We report Nectonema sp. as the first record of a marine nematomorph parasitic in isopod crustaceans. This is also the third record of marine nematomorphs from the North Pacific. Six infected isopods (Natatolana japonensis) collected from 1425 m of depth in the Sea of Japan each contained one to seven (mean 2.33) nematomorphs in the body cavity in the pereon. There was no correlation between the host body length and number of parasites. For Nectonema sp., we describe and illustrate morphological features of the parasitic juvenile stage and present nucleotide sequences for the cytochrome c oxidase subunit I gene (COI or cox1; 451 nt), 18S rRNA gene (1777 nt), and region spanning the internal transcribed spacer 1 (ITS1) and the 28S rRNA gene including the 5.8S rRNA gene and ITS2 (1218 nt in total). In an 18S maximum-likelihood tree that included 24 nematomorph species, Nectonema sp. grouped with N. agile from the northwestern Atlantic; the 18S gene from these two taxa was divergent by 11.8% K2P distance, suggesting that they are different species. Nectonema species may have a broader range of host groups than previously suspected, but may have been previously misidentified as nematode parasites.

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.

Heterocypris spadix sp. nov. (Crustacea: Ostracoda: Cypridoidea) from Japan, with Information on Its Reproductive Mode.

We describe the cypridoidean ostracod Heterocypris spadix sp. nov. from brackish water on Okinawa Island, Japan. The species closely resembles Heterocypris salina (Brady, 1868) but differs in that (1) the marginal infolds on valves are less developed, (2) the tubercles on the anterior margin of the right valve are completely covered by the selvage and invisible in inner view, and (3) the calcified inner lamella on the ventral margin of the left and right valves is scarcely evident in inner view, as the ventral margins of the valves bend inwardly. We determined partial sequences for the cytochrome c oxidase subunit I (COI; cox1) and 18S rRNA genes in H. spadix for future DNA barcoding and phylogenetic analyses. Our sample contained only females. A breeding experiment revealed that H. spadix females reproduce parthenogenetically. Another experiment showed that H. spadix has low tolerance to desiccation, with all individuals at 25°C dying between 1-2 hours after removal from water. We amplified and sequenced a partial 16S rRNA sequence for the endosymbiotic bacterium Cardinium from H. spadix. Infection by Cardinium may be related to the parthenogenetic reproductive mode we observed in H. spadix.

A new species of Nicippe from the Bering Sea (Crustacea, Amphipoda, Pardaliscidae), with a redescription of N. tumida.

A new pardaliscid amphipod, Nicippe beringensis, is described from the Bering Sea at depths between 520 and 536 m, and N. tumida Bruzelius, 1859 is redescribed based on specimens from Fredrikshald, Norway, near the species' type locality. Nucleotide sequences of mitochondrial cytochrome c oxidase subunit I (COI) from the holotype and a paratype of N. beringensis sp. nov. are reported. While N. beringensis sp. nov. is similar to N. tumida, it differs from the latter in having an asetose palp article 1 of maxilla 1, a gnathopod 1 coxa with a straight distal edge, and in the posterior margin of the basis of gnathopods 1 and 2, and pereopod 3, being heavily setose in females. A key to species of Nicippe is provided.

New replacement name for a homonym in Lepeophtheirus (Crustacea: Copepoda: Caligidae).

Markevich (1940) established Pseudolepeophtheirus Markevich, 1940 for Pseudolepeophtheirus longicauda Markevich, 1940 based on copepods collected from the pleuronectid fish Platichthys stellatus (Pallas, 1787). Dojiri Ho (2013) synonymized the genus and the species with Lepeophtheirus Nordmann, 1832 and Lepeophtheirus parvicruris Fraser, 1920, respectively. Later, Homma et al. (2020) resurrected Markevich's species as a member of Lepeophtheirus, i.e., as L. longicauda (Markevich, 1940). The last component of the names of both genera is 'phtheirus' (transliterated from the Greek φθειρ; Nordmann 1832: 30), a masculine noun, and thus under Article 30.1.2 of the International Code of Zoological Nomenclature (hereinafter, Code; International Commission on Zoological Nomenclature 1999), both generic names are also masculine. The species-group name longicauda might be regarded as either a noun in apposition or as an adjective in the feminine gender, and Markevich (1940) did not specify his intention in this regard. Bearing in mind that 'cauda', meaning 'tail', actually is a feminine Latin noun and that Markevich did not change the final '-a' to '-us' to match the masculine gender of the genus, we deem that longicauda Markevich, 1940 is a noun in apposition, a position supported by Article 31.2.2 of the Code.

First in Situ Observations of Behavior in Deep-Sea Tanaidacean Crustaceans.

We report on the behavior of a deep-sea tanaidacean, Gigantapseudes sp. (Apseudomorpha: Gigantapseudidae), recorded at the depths of 6446-6447 m by the manned submersible Shinkai 6500. From recordings of at least three individuals walking on the sea floor, we confirm that Gigantapseudes sp. is epibenthic, as previously inferred from leg shape. One individual was recorded entering a hole. All individuals in the videos kept pereopods 4 raised from the seafloor while walking, implying that those legs have a function other than for walking, such as mechano- or chemoreception, or posture control. Our in situ observations of behavior are the first for any deep-sea tanaidacean and illustrate the importance of recording high-resolution videos in the deep sea and archiving them for future use. Our identification of Gigantapseudes sp. from video footage provides the first record of this genus from Japanese waters and extends the northern limit of the known generic distribution.

Integrative taxonomy of Pseudolepeophtheirus longicauda (Crustacea: Copepoda: Caligidae) parasitic on Platichthys stellatus (Actinopterygii: Pleuronectidae).

Based on specimens from the gill cavities of one Platichthys stellatus individual collected in the Sea of Japan, we investigated the taxonomic status of the enigmatic caligid genus Pseudolepeophtheirus and its type species, Pseudolepeophtheirus longicauda. In a maximum likelihood (ML) tree based on 18S rRNA gene sequences, the sequence from our sample was nested in a well-supported Lepeophtheirus clade, along with the type species, confirming that Pseudolepeophtheirus should be considered a junior synonym of Lepeophtheirus; our morphological data support this synonymy. Although a previous study had synonymized Pseudolepeophtheirus longicauda with Lepeophtheirus parvicruris, we found that the former differs morphologically from the latter in having a short leg-4 exopod, with the articulation between the first and second segments not evident (the shape of the posterior striated membrane on the leg-2 intercoxal sclerite also differs between two species), and detected slight differences in 18S rRNA sequences between two taxa. We thus concluded that this synonymy is invalid, and reinstate Lepeophtheirus longicauda as a valid species. A ML analysis of COI sequences from Pl. stellatus (the host fish for both L. longicauda and L. parvicruris) showed the host species to comprise distinct northwestern- and northeastern-Pacific clades. Lepeophtheirus longicauda is distributed in the northwestern Pacific and L. parvicruris in the northeastern Pacific, indicating co-divergence of the two copepod species with the host lineages.