Discovery of a new fan worm species in Suruga Bay by joint group from Yokohama National University, Tokai University and Nagoya University

A group led by Professor Eijiroh Nishi of Yokohama National University, Professor Katsuhiko Tanaka of Tokai University, and Lecturer Naoto Jimi of the Graduate School of Science at Nagoya University has discovered a new species of the family Sabellidae in the class Polychaeta in the phylum Annelida from sandy mud sediments about 50 meters deep off Nihondaira, Suruga Bay. Euchonoides shizuoka (Futamaki-keyarimushi) from Suruga Bay was given the Japanese name of Futamaki because it has two belly warmer-like structures. Its scientific name (species), shizuoka, was adopted because specimens were collected in Shizuoka Prefecture. The study was published in Plankton and Benthos Research.

Suruga Bay is known as the deepest bay in Japan, and deep-sea organisms, including fishery target species such as the Japanese spider crab (Macrocheira kaempferi) and sakura shrimp (Lucensosergia lucens), have often attracted attention. Meanwhile, most previous reports on marine organisms in shallow coastal waters are fragmentary, and our knowledge of them is insufficient. Tanaka's group at Tokai University has been conducting surveys of benthic organisms by mud sampling in the coastal areas of the inner part of Suruga Bay, using the small training vessel "Southern Cross" and other vessels owned by Tokai University. They asked Professor Nishi of Yokohama National University to check samples of annelid polychaetes obtained in the survey process, and an unknown fan worm species was found in the samples. They also collaborated with Jimi of Nagoya University and others and described this fan worm as a new species.

There are about 1,500 species of annelid polychaetes in the seas around Japan, including 56 species in 23 genera recorded in the family Sabellidae. The description of the genus Euchonoides in this paper by the research group is the first record in Japan, and Euchonoides shizuoka is also a new species. Thus, the distribution of 57 species in 24 genera in the family Sabellidae along the Japanese coast is now confirmed.

The new species discovered in this study is a member of the genus Euchonoides of the family Sabellidae and has the scientific name of Euchonoides shizuoka and a Japanese name of Futamaki-keyarimushi. The specimens measured 1.7-2.4 mm in length and 0.1-0.2 mm in width; and had 3 pairs, 6 in total, of radioles measuring 0.5-1.0 mm in length; and 8 thoracic and 9 abdominal segments, with inflation on the second thoracic segment and the second and third abdominal segments, and membrane-like projections on the seventh to ninth abdominal segments.

The genus Euchonoides is characterized by the presence of inflation on the second thoracic segment, a membrane-like projection on the posterior end of the abdomen, and a clitellum-like circumferential ridge on the third abdominal segment. Previously, only E. moeone from Hawaii and E. bicincta from the Russian coast of the Peter the Great Gulf have been known. The new species is distinguished from these two species by the presence of a lateral incision on the collar, inflation on the second abdominal segment, and a different arrangement of chaetal dentition.

The specimens of this new species are registered and held at the Coastal Branch of Natural History Museum and Institute, Chiba, in Katsuura City, Chiba Prefecture, and the Museum: School of Marine Science and Technology, Tokai University.

In addition to E. shizuoka found in this study, the samples from the survey of marine organisms in the shallow coastal waters of Suruga Bay may contain many newly recorded and undescribed species. Many important results are expected to be produced by further reviewing the samples. In fact, a sample that appears to be an Euchonoides species has been found among the samples collected in a coastal area of the Tohoku region, and the research group is currently conducting a taxonomic study on the sample. They will continue surveys and research on very small-sized annelids, which remain practically uninvestigated.

Journal Information
Publication: Plankton and Benthos Research
Title: A new species of Euchonoides (Annelida, Polychaeta, Sabellidae) from Suruga Bay, Japan
DOI: 10.3800/pbr.19.203