Discodorididae sp. 1

Location: Usami, Shizuoka, Japan
Date: 2015/12/30
Length: ??mm
Depth: 14.0m
Water temperature: ??℃

Description

A medium-sized dorid of the family Discodorididae, reaching 40-70 mm in body length. The body is oval and slightly arched, with the dorsal notum densely covered by conical tubercles bearing internal spicules. The ground colour is greyish to chocolate brown, overlaid with irregular darker blotches that vary widely between individuals, although a series of oval dark patches arranged regularly on either side of the midline is consistent across the species. The rhinophores share the ground colour and bear fine brown speckling, with roughly 30 or more lamellae. The branchial tuft consists of six tripinnate plumes that match the ground colour and are dusted with brown dots. The underside (hyponotum and foot) is the same colour as the dorsum and bears numerous small dark spots; a dark ring running around the foot on the hyponotum is a key feature for identifying the species. When disturbed, the animal readily autotomises the mantle margin.

Distribution

The type locality is Choshaga Saki in Sagami Bay, Honshu, Japan, based on a specimen collected in 1970. The species has so far been recorded along the warm-temperate coasts of Japan from Kyushu to central Honshu.

Remarks

An undescribed species without a formal binomial. Dayrat 2006, in his major revision of the Discodorididae, treated it as Discodorididae sp. C (also referable to as "Metadiscodoris" sp. C). The penis carries a diagnostic series of four to five rings of conical hooks near its apex, an organ that distinguishes the species clearly from other discodorid dorids. Earlier Japanese guidebooks identified it as Discodoris concinna (Alder & Hancock, 1864), but that species is now considered restricted to the Indian Ocean. It is also distinct from Tayuva lilacina (Gould, 1852), which has much smaller dorsal tubercles.