Japonactaeon nipponensis (Yamakawa, 1911)

Location: Wakayama, Japan
Date: 2026/03/14
Length: 10mm
Depth: 0.1m
Water temperature: 10.0℃

Description

A small species of Acteonidae, about 10 mm in shell height. The shell is ovate to subcylindrical, with a white to pale background marked by darker spiral bands. The contrast between light and dark bands varies considerably between individuals: typical southern Japanese specimens show clear white bands, while populations from northern Honshu and the Russian Far East often accumulate more black pigment and appear overall darker. The shell surface is essentially smooth but bears fine spiral striae in its upper and lower portions. The soft body is black.

Distribution

Type locality: Pleistocene (diluvial) deposits in the Tokyo area, where the species was originally described from fossil material; the type specimens are now lost. Living specimens have since been recorded along the coast of Japan (mainly from western Honshu to Kyushu, with some northern Honshu records), southern Korea, and Peter the Great Bay (Sukhodol and Telyakovskogo bays) in the Russian Far East. The species inhabits tidal flats and shallow water down to about 5 m.

Etymology

The specific epithet nipponensis is Latin for "from Japan", in reference to the species being described from Japanese material.

Remarks

The genus Japonactaeon was erected by Iwao Taki in 1956 for East Asian coastal members of the family, and the present species is its type. The colour-pattern differences seen between Japanese and Russian populations were once thought to represent distinct taxa, but molecular phylogenetic analysis has shown the two populations to be conspecific. In Japan the species is listed as Near Threatened in the Ministry of the Environment Red Data Book, and is regarded as a representative tidal-flat species of East Asia whose habitat is rapidly being lost to coastal development, reclamation, and water pollution.