Dermatobranchus semistriatus Baba, 1949

Location: Engetsutou, Sirahama, Wakayama, Japan
Date: 2023/01/09
Length: 22mm
Depth: 1.0m
Water temperature: 17.0℃

Description

A small Arminidae, body length about 2 cm. The dorsal longitudinal folds are extremely fine and numerous (20-25 in count) — distinctively paler than in the related Dermatobranchus striatus and Dermatobranchus striatellus. Ground colour pale greyish-yellow, with many dark longitudinal lines and small black dots irregularly arranged along these lines. Rhinophores black; the head-veil margin, mantle, and foot margin pale yellow. Ventral body white. Black fine dots may sometimes be scattered on the foot margin and body sides. The masticatory edge of the jaw plate bears 1-2 rows of spinous scale-teeth. The radula bears characters distinguishing it from the three related species. Radula formula 25×50-60.1.1.1.50-60. The central tooth has 11-14 denticles on each side of the median cusp; the first lateral is asymmetric, narrow, with only 8-9 denticles; among the second and following laterals, 4-5 bear 5-3 denticles, with the rest decreasing outward.

Distribution

Type locality is Hayama-Samejima, Sagami Bay (intertidal, July-August 1939, 5 specimens) and Hayama-Najima, Sagami Bay (intertidal, August-September 1939, 3 specimens). The original description (Baba, 1949) records the species only from Sagami Bay.

Etymology

The specific epithet semistriatus is a Latin compound of semi- (half) and striatus (striped), reflecting the fine, numerous (20-25) dorsal folds. The original description does not give an explicit etymology paragraph. The Japanese name "Sagiri-otome-umiushi" likens the pale greyish-yellow ground to "sagiri" (fine mist).

Remarks

Resembles Dermatobranchus striatus and Dermatobranchus striatellus, but distinguished by (1) extremely fine and numerous (20-25) dorsal folds, (2) a paler greyish-yellow ground colour, and (3) an asymmetric first lateral tooth bearing only 8-9 denticles.