• 1 Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan,
  • 2 College of Arts and Sciences, J. F. Oberlin University, Machida, Tokyo 194-0294, Japan
  • 3 Sugashima Marine Biological Laboratory, Graduate School of Science, Nagoya University, Toba 517-0004, Japan
  • 4 Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
  • 5 Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi, Yamaguchi 753-8512, Japan
  • 6 Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
Zoolog Sci, 2023 Jun;40(3):262-272.
PMID: 37256573 DOI: 10.2108/zs220105


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.

* Title and MeSH Headings from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.