The 2019 symposium of the Japanese Society of Systematic Zoology, entitled ‘Current taxonomic studies on invertebrate fauna in Kumano Sea’ was held on the occasion of the 90th annual meeting of the Zoological Society of Japan in Osaka City University during 12 to 14 September 2019. The five interesting talks were given by the special invited speakers: Hidetaka Furuya ‘Dicyemid fauna in the Kumanonada-Sea’; Takato Izumi ‘Isactinernus quadrilobatus Carlgren, 1918 (Anenthemonae: Actinernidae) collected from the Kumano Sea-To put an end to the taxonomical confusion by the specimen for a century!’; Masanori Okanishi ‘Ophiuroids from the Kumano Sea’; Naoto Jimi ‘Survey of benthic fauna in the Kumano Sea by T/S Seisui-Maru’: Takeya Moritaki ‘Collaboration between aquarium and researchers on invertebrates from Kumano Sea’.

Dicyemids (phylum Dicyemida) are endosymbionts that typically are found in the renal sac of benthic cephalopod molluscs. The dicyemid bodies consist of only 8 to 40 cells, which are the fewest in number of cells in metazoans, and are organized very simply. Typically, two or three dicyemid species are found in a single specimen of the host, and most of them show high host specificity. Dicyemid species have been examined in the benthic cephalopods collected from the Kumano Sea at a seafloor depth of 150–400 m using bottom trawl nets since 2013. Twenty-five undescribed species of dicyemids, included in five genera, were found in 15 species of cephalopods. There is a considerable diversity of dicyemids in relatively narrow range of localities of the Kumano Sea. Here current taxonomic studies on dicyemid fauna in the Kumano Sea are briefly reported.

Isactinernus quadrilobatus Carlgren, 1918, the only species of genus Isactinernus, is characterized by an oral disc with four equally-sized lobes. In 2003 Synactinernus flavus Carlgren, 1918, which is characterized by four large and four small lobes alternately arranged, was synonymized into I. quadrilobatus because the difference of lobe shape was thought to be intraspecific variation, and thus the genus Synactinernus was also synonymized into Isactinernus. However, our molecular phylogenetic analysis of Actinernidae including I. quadrilobatus collected from the Kumano Sea revealed that I. quadrilobatus is genetically distinct from S. flavus. Our morphological comparison between the two species supported the result of the molecular analysis. Consequently, the genus Synactinernus was re-established and separated from Isactinernus. Additionally, during this study, we discovered and described an additional species of the genus, Synactinernus churaumi Izumi and Fujii, 2019.

The Ophiuroidea is numerically the largest class of echinoderms and can be found in a great variety of marine habitats such as: in the interstices of sponges and hard corals; on muddy ground; infaunally buried in sediments; under rocks; and on the surfaces of various animals such as soft corals. Twenty one species have been recorded from the Kumano Sea, off the Kii Peninsula, central Japan but no surveys of this region have been performed since 1980. During the benthic faunal surveys of the Kumano Sea in 2013 by the fishing vessel Syouei-Maru and in 2016 to 2019 by the T/S Seisui-Maru of Mie University, 64 ophiuroid species from 14 families were recorded.

The Kumano Sea has wide-range depths and various environments of the deep seafloor. Inventory of benthic animals is poorly known around the sea because there were few research cruises or investigations in this area. In this situation, training/research vessel (T/RV) Seisui-maru that belongs to Mie University plays a role of center of excellence for investigation of marine science around the Kumano Sea. The vessel has the ability to operate various kinds of research equipment for the benthos survey and conducts many training cruises. Recently, the last author has held annual training/research cruises in the Kumano Sea from 2009 to 2019. Over 16 phyla were recorded, and some of the new species were described based on specimens collected during the cruises. In this paper, we provide an introduction of Seisui-maru, a summary of benthos research at the Kumano Sea, and brief records of polychaetes collected during the cruise in 2017.

Toba Aquarium regularly collects marine invertebrates from the Kumano Sea on the Pacific coast of central Japan. These animals are mainly used for exhibition in the aquarium as well as for taxonomic studies. When the taxonomic status of the animals is uncertain, we work with researchers to observe the specimens of those marine invertebrates. From 2006 to 2019, 382 species from 12 phyla have been so far recorded from the bathyal zone of Kumano Sea. Together with 26 researchers, we examined a total of 103 species collected during the surveys and nine out of them were described as new species. Using our rearing techniques, some interesting behaviors of the bathyal marine invertebrates were observed with live specimens in the aquarium.

Thirty-two specimens (124.1–365.0 mm standard length) of Saurida undosquamis (Richardson, 1848) (Aulopiformes: Synodontidae), previously recorded from the Indo-West Pacific from Persian Gulf, Chagos Archipelago, Andaman Sea to Taiwan, Southeast Asia, Papua New Guinea and northern half and southwestern Australia, were collected from the mainland of Kagoshima Prefecture and Tanega-shima island in the Osumi Islands, southern Japan. These specimens represent the first records of S. undosquamis from Japanese waters and include the northernmost records (Kasasa, west coast of Satsuma Peninsula) for the species. The Japanese specimens are described here in detail and the new Japanese name “Tsukeage-eso” is proposed for the species.

One of the major crustacean groups, Maxillopoda had accommodated Mystacocarida, Copepoda, Thecostraca, Tantulocarida, Ostracoda, Branchiura, Pentastomida, and some fossil taxa, and was generally defined by some combinations of the following characters: body tagma composed of 5 cephalic, 6 (or 7) thoracic and 5 (or 4) abdominal somites; male gonopore (s) located on the first abdominal somite; uniramous antennules; naupliar eyes with tapetal cells, and so on. However, the monophyly of maxillopodans is totally rejected by a number of genetic analyses, while palaeontological and morphological approaches still recognize not only maxillopodans but also entomostracans as valid taxa. Since this issue is not well documented in Japan, the present paper briefly introduces modern phylogenetic studies on maxillopodan crustaceans, in particular Copepoda and Ostracoda.

A single specimen (166.0 mm standard length) of Peristedion riversandersoni (Alcock, 1894) (Teleostei: Peristediidae), previously recorded in Japanese waters from off Toyama Prefecture in the Sea of Japan, the Pacific coast from Ibaraki to Miyazaki prefectures, and the East China Sea, was recently collected from off Iwate Prefecture, northern Japan. This specimen representing the northernmost record for P. riversandersoni is described herein. In addition, coloration of fresh and preserved specimens of P. riversandersoni are emphasized as newly recognized diagnostic characters for this species based on a comparative examination of 29 specimens of P. riversandersoni, including the Iwate specimen, with 70 specimens of Peristedion orientale Temminck and Schlegel, 1843.

A new revision of the higher taxonomic classification of eukaryotes was published in 2019 in the journal of the International Society of Protistologists, Journal of Eukaryotic Microbiology. In the seven years since the last revision made in 2012, the large-scale multigene phylogenetic analyses in the background of the recent advancement of sequencing technology have revealed the affiliation of many “orphan” lineages and taxa. The major changes in this revision are the following four points: i) Excavata is not adopted to be a clade, ii) CRuMs as an assembly of Collodictyonida, Rigifilida, and Mantamonas is adopted to be a clade as the relatives of Amorphea, iii) Haptista consisted of Haptophyta and Centrohelida is adopted as a new clade, and iv) Crypista is also adopted as a new clade.