The phylogenetic relationships of Syllidae have been analyzed in several studies during the last decades, resulting in highly congruent topologies. Most of the subfamilies were found to be monophyletic, while other groups (Eusyllinae and several genera) have been reorganized attending their phylogenetic relationships. However, there are still several enigmatic genera, which could not be assigned to any of the established subgroups. These enigmatic genera usually show a combination of characters indicating relationships with several different groups, and some show morphological traits unique to Syllidae. One of the most intriguing genera, still unclassified within Syllidae is Clavisyllis Knox. Herein, we provide a complete description of a new species Clavisyllis tenjini n. sp. from Japan. We sequence the complete mitochondrial genome, compare with the available data from other syllids, and perform a phylogenetic analysis of three genes (18S, 16S, COI), traditionally used in previous studies. Clavisyllis shows a unique combination of characters within Syllidae, such as nuchal lappets and large ovoid dorsal cirri. The new species has additional anterior appendages that have not been found in any other syllid. Our results show the genus is a member of Eusyllinae, closely related to Pionosyllis Malmgren. The mitochondrial gene order agrees with the considered plesiomorphic gene order in Annelida, which is present in all members of Eusyllinae investigated so far. Clavisyllis reproduces by epigamy, the reproductive mode of members of Eusyllinae. The present study contributes to the systematics of Syllidae, a complex group with a large number of species and striking reproductive modes.
Whilst seven species of magelonids have been originally described from the North-Western Pacific Ocean, only two have been from Japanese waters. Given the often high diversity of magelonid species within relatively small regions, the number of Japanese Magelona species is likely to be higher. The validity of several recorded species from the region has been additionally called into question, and the urgent need for a review of magelonids of Japan highlighted. Newly collected samples of magelonids have emphasised the presence of three species new to science occurring off Japan, herein described: Magelona alba sp. nov., Magelona armatis sp. nov., and Magelona boninensis sp. nov. A redescription of Magelona japonica is additionally provided, along with notes on a fifth species, which approaches Magelona cornuta. A dichotomous identification key to magelonid species of the North-Western Pacific Ocean, along with a table of characters for all five observed species is provided.
Four new species of annelids, Ctenodrilus japonicus sp. nov., Raphidrilus misakiensis sp. nov., Raphidrilus okinawaensis sp. nov., and Raricirrus anubis sp. nov., are described based on specimens collected from Japanese waters. Ctenodrilus japonicus sp. nov. inhabits the interstitial environment and can be distinguished from the other congeners by the following features: (i) total of 16 chaetigers, (ii) chaetigers 1-3 with stout hooks, (iii) minute body (approximately 1 mm in length), (iv) all parapodia with the same number of chaetae (two notochaetae; two neurochaetae), and (v) presence of dorsal and ventral papillae. Raphidrilus misakiensis sp. nov. lives under intertidal stones and can be distinguished from other congeners by having pectinate neurochaetae. Raphidrilus okinawaensis sp. nov. inhabits the interstitial environment and can be distinguished from other congeners by: (i) absence of annulation on the peristomium and achaetous segment and (ii) presence of a heart body in chaetigers 4-5. Raricirrus anubis sp. nov. inhabits whale bones and can be distinguished from other congeners by the following features: (i) presence of a heart body in chaetigers 9-14, (ii) presence of capillary neurochaetae on chaetiger 1, and (iii) presence of simple curved spines. A phylogenetic tree based on partial sequences of cytochrome c oxidase subunit I and 16S rRNA from the new species and other cirratulid worms showed that Raphidrilus is included in Cirratuliformia. This is the first record of Raphidrilus and Raricirrus from Japanese waters.
A new species of Spirobranchus (Annelida: Serpulidae) is described based on specimens collected at the coastal Shonan area of Sagami Bay and the adjacent areas of Honshu, Japan. Spirobranchusakitsushima sp. nov. forms large aggregations in the intertidal rocky zone of warm-temperate Japanese shores. This species was referred to as Pomatoleioskraussii (Baird, 1864) until the monotypic genus Pomatoleios was synonymized with Spirobranchus. This new species is formally described based on morphologically distinct Japanese specimens with supporting DNA sequence data. The calcareous opercular endplate of Spirobranchusakitsushima sp. nov. lacks a distinct talon, but some specimens have a slight rounded swelling on the endplate underside, while in other species of the S.kraussii complex a talon is present, usually extended, and with bulges. We examined sub-fossil tube aggregations of the new species and suggest that such aggregation stranded ashore is a good indicator of vertical land movements (uplift and subsidence) resulting from past events, such as earthquakes, in Honshu, Japan.
We establish a new interstitial polyclad species, Theama japonica sp. nov., based on specimens collected from coarse-sandy habitats in three Japanese main islands (Hokkaido, Honshu, and Shikoku) along the coasts of the Pacific Ocean and the Sea of Japan. Theama japonica is characterized by i) two pairs of cerebral eyespots and four to six precerebral eyespots; ii) eosinophilic secretion glands distributed in the distal half of the inner ventral part of the prostatic vesicle; iii) a conical penis papilla, bent up dorsally, with a sclerotized inner wall; iv) the prostatic sheath with an inner angular fold on the dorso-distal side; and v) the external cilia longer dorsally than ventrally. Partial sequences of the cytochrome c oxidase subunit I (COI) gene from 20 specimens collected at eight localities along Japanese coasts represented 19 haplotypes. The uncorrected p-distances among these COI haplotypes fell within intraspecific variations observed in other polyclads. A network analysis based on these COI haplotypes suggested a geographically non-cohesive genetic structure of the species, possibly indicating the species' high dispersibility. Molecular phylogenetic analyses based on a concatenated dataset of 18S and 28S rDNA sequences showed T. japonica formed a clade with other Theama species. The resulting tree also indicates that our new species is more closely related to Theama sp. from Colombia than species from Panama and Croatia.
A new fish leech, Branchellion brevicaudatae sp. n., is described based on specimens parasitizing the gills of the short-tail stingray, Bathytoshia brevicaudata (Hutton, 1875), collected from Japanese waters. The new species can be distinguished from other congeners by having: i) pulsating vesicles emerging from posterior base of branchiae, one pair per somite; ii) dorsal white spots, not arranged in longitudinal row; and iii) blackish body. A phylogenetic tree based on partial sequences of the mitochondrial cytochrome c oxidase subunit I gene from the new species and other piscicolid worms showed that the new species is sister to Branchellion torpedinis Savigny, 1822. This is the first record of Branchellion Savigny, 1822 from Japanese waters.
Two new species of Hesionidae, Parahesione pulvinata sp. nov. and Parahesione apiculata sp. nov. are described based on materials collected at tidal flats in Okinawa (Japan) from burrows of the ghost shrimps Neocallichirus jousseaumei and Glypturus armatus. The two new species are characterized by having eight enlarged cirri, dorsal cirrophores with dorsal foliose lobe and biramous parapodia, and by lacking median antenna. Parahesione apiculata sp. nov. has digitate lobes on the posterior margin of the dorsal foliose lobe (absent in P. pulvinata sp. nov.). The two new species were never found outside the ghost shrimp burrows, suggesting they are obligate symbionts. Phylogenetic analyses based on four concatenated genes suggest that the symbiotic lifestyle has evolved several times in Hesionidae.
Bioluminescence, a phenomenon observed widely in organisms ranging from bacteria to metazoans, has a significant impact on the behaviour and ecology of organisms. Among bioluminescent organisms, Polycirrus, which has unique emission wavelengths, has received attention, and advanced studies such as RNA-Seq have been conducted, but they are limited to a few cases. In addition, accurate species identification is difficult due to lack of taxonomic organization. In this study, we conducted comprehensive taxonomic survey of Japanese Polycirrus based on multiple specimens from different locations and described as three new species: Polycirrus onibi sp. nov., P. ikeguchii sp. nov. and P. aoandon sp. nov. The three species can be distinguished from the known species based on the following characters: (i) arrangement of mid-ventral groove, (ii) arrangement of notochaetigerous segments, (iii) type of neurochaetae uncini, and (iv) arrangement of nephridial papillae. By linking the bioluminescence phenomenon with taxonomic knowledge, we established a foundation for future bioluminescent research development. We also provide a brief phylogenetic tree based on cytochrome c oxidase subunit I (COI) sequences to discuss the evolution of bioluminescence and the direction of future research.