Goniobranchus geminus (Rudman, 1987)

Description

The mantle margin shows four colour bands from outside to inside: a thin outermost white band, then a translucent greyish-purple band, then a white band, and innermost a bright golden-yellow band. Inside the golden band the dorsum is gold-brown to dirty yellow, scattered with circular bluish-purple spots of varying size, each ringed by a thin white circle. Rhinophore stalk translucent white, club translucent gold with brownish lamellae. Gills sub-quadrangular: outer face white with translucent brown lamellae, inner face brown above and white basally. Submarginal mantle glands secrete a white fluid when the animal is disturbed. A diagnostic behaviour is rhythmically raising and lowering the entire mantle edge while crawling, shared with Goniobranchus kuniei. Reaches 59 mm in body length alive.

Distribution

Type locality is Fungu Mkadya off Kunduchi, Dar es Salaam, Tanzania (sublittoral, January 1974). An Indian Ocean species recorded from Tanzania, Réunion, Christmas Island (Indian Ocean), and the Red Sea (photographs). It is the geographic replacement of the western-Pacific Goniobranchus kuniei; the two species meet at Christmas Island.

Etymology

The specific epithet geminus is Latin for twin, referring to the close apparent relationship between this species and Goniobranchus kuniei (verbatim from the original description).

Remarks

A sibling species of Goniobranchus kuniei, distinguished by (1) a four-banded mantle border (white-purple-white-yellow), versus three purple bands in Goniobranchus kuniei, and (2) the absence of the diffuse milky-yellow ring around each white-ringed purple spot. Chromodoris geminus Rudman, 1987 is the original combination, later transferred to Goniobranchus.

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References

• Goniobranchus geminus, Johnson R.F. & Gosliner T.M. (2012). Traditional taxonomic groupings mask evolutionary history: a molecular phylogeny and new classification of the chromodorid nudibranchs. PLoS ONE 7(4): e33479.
• Goniobranchus geminus, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.