Costasiella sp from Sulawesi

March 20, 1999
From: Lindsay Warren


Here is another mystery from Tukang Besi Islands, [Sulawesi, Indonesia - Operation Wallacea ]

Length: 3 mm.  Simple rhinophores, white with transparent tip and base.  Black collar around 'neck' behind rhinophores.  White oral veil. Distinct eye spots.  Cerata had black base with "most incredible dazzling colours on cerata - primarily pinks and greens like tinsel.  Cerata nearer the foot were shorter and generally primarily black with green tip.
Underside shows translucent edge to foot with just green and pink sparkle."
Notum never visible due to clustered cerata.  Tail white and very thin. Found at a depth of 5 m in between Sarcophyton soft coral on rubble covered in algal growths.  This was referred to as the 'Christmas Tree Nudibranch'!
Photo: Adam Powell.

All the best

Warren, L., 1999 (Mar 20) Costasiella sp from Sulawesi. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Lindsay,
My first thought was that it looks like a species of Cuthona, but the apparent lack of oral tentacles on the oral veil suggests it is not. Thanks for the field notes and sketches which confirm their absence. I think it is a sacoglossan and the eyes set closely together are characteristic of the genus Costasiella. Ichikawa (1993) described quite a few species of Costasiella from the Ryukyu Islands and one of these, Costasiella iridophora is similarly speckled with iridescent specks. However your animal has a very characteristic black "collar" behind the eyes which I have not seen described for a species of this genus so it is probably a new species.

Bill Rudman.

Ichikawa, M. (1993) Saccoglossa (Opisthobranchia) from the Ryukyu Islands. Publications of the Seto Marine Biological Laboratory, 36: 119-139.

Rudman, W.B., 1999 (Mar 20). Comment on Costasiella sp from Sulawesi by Lindsay Warren. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Costasiella sp. 1.

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