Acteocina gordonis (Yokoyama, 1927)

Location: Ipponmatu, Osezaki, Shizuoka, Japan
Date: 2020/01/29
Length: 5mm
Depth: 15.0m
Water temperature: 18.0℃

Description

A very small acteocinid about 3.4 mm in shell height. The shell is thick and subcylindrical, with a high conical spire and a bluntly rounded apex. The four and a half whorls each bear a distinct spiral ridge in the middle; above this ridge the whorl is slightly concave at the shoulder. The shell surface is entirely smooth, lacking incised lines or ribs. The aperture is elongate and slightly shorter than the shell-height: linear in the upper part, gradually widening downwards, and broadest and rounded at the lower end. A strong, oblique, blunt columellar fold is present. The glaze covering the inner lip spreads outward from its lower part and covers part of the shell-base. The outer lip is rather thick.

Distribution

Type locality: Matsudo, in northern Chiba Prefecture, Japan (former Western Shimosa Province). The species was described as a fossil from the Upper Musashino Formation (Pleistocene), based on a single specimen contained in the fossil shell collection kept at the Geological Institute of the Imperial University of Tokyo. The species has subsequently been recorded from the Recent fauna of Japan as well.

Etymology

The specific epithet gordonis honours the late Mr. Gordon Yamakawa, whose collection of fossil shells from the Upper Musashino Formation was kept at the Geological Institute of the Imperial University of Tokyo. The describer, Matajiro Yokoyama, found this and several other new species while examining Yamakawa's collection.