Thordisa oliva J. M. Chan & Gosliner, 2007

Location: Ushitsuki Rock, Kumomi, Shizuoka, Japan
Date: 2022/01/25
Length: 8mm
Depth: 6.0m
Water temperature: 16.5℃

Description

A small species, 6–10 mm in length, with an oval, low-profile body. The mantle background is a dark olive-green, which is the source of the species name. Tan, conical papillae and rounded tubercles are dispersed across the dorsum, with the longest papillae concentrated towards the middle. The rhinophoral sheath is mostly smooth but bears two curved tubercles protruding from opposite sides. Rhinophores are perfoliate with 10 lamellae. The gill is completely retractile, tripinnate, with six branches and opaque white apices. A pair of small pits on the lateral sides of the mouth is a key diagnostic feature. Living animals are encrusted with sand particles.

Distribution

Type locality: Jesser Point, Sodwana Bay National Park, South Africa, 2 m depth (Holotype SAM A35375, 6 May 1982). A paratype (CASIZ 144079) was collected by Atsushi Ono at Zamami Island, Kerama Islands, Okinawa, Japan, at 7 m depth on 14 June 2000. At the time of the original description (Chan & Gosliner, 2007) the species was known from both South Africa and Japan.

Etymology

From the Latin word oliva ("olive" or "olive tree"). The original description (Chan & Gosliner, 2007) states that the name was used to describe the olive-green colour of the mantle.

Remarks

One of five new species described in the original revision. It is inferred to be the sister species of Thordisa diuda Marcus, 1955 (from Brazil), with which it shares a rare combination of olive-green mantle colour, two large papillae flanking the rhinophore opening, and a pair of distinctive pits beside the mouth. Thordisa oliva differs in having a vestibular gland composed of two nodules with a single spine and bifurcated inner lateral teeth, whereas T. diuda has a single pouch-shaped, unarmed vestibular gland and simply hamate inner laterals.