Costasiella usagi
Ichikawa, 1993

Family: Costasiellidae


Tropical western pacific


Upper: On sandy bottom at 16-18m, Watsons Bay, Lizard Island, QLD, Australia, late December 2003. 3-5mm long. Photo: Nils Anthes
Lower: Photo showing two extreme colour variations together on their food algae Avrainvilla. 4.5mm (dark form), 6.0mm (light form); Cocos Lagoon, Guam. 25 January 1989. Photo: C. Caelson & P.J. Hoff.

From Carlson & Hoff's messages Costasiella usagi is very variable in colour. In Ichikawa's description the colour is described as:
"The head and tail are not pigmented,, and the rhinophores are black. The median cerata are grey, while the outer ones are black. All the cerata possess a white end and a black tip. Moreover, all the cerata bearl longitudinal striations reaching from the base of each ceras to the white apical portion. ... The ventral side of the foot is white. .... Smaller specimens have the median cerata coloured green, instead of grey."

Ichikawa doesn't say what colour the longitudinal striations are but apparently they are white. From photos on the Forum, the rhinophores range from completely black to black edged, and in some specimens green can be the predominate colour in all cerata. This is certainly a good example of the dangers of describing new species prematurely.

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

Authorship details
Rudman, W.B., 2004 (January 9) Costasiella usagi Ichikawa, 1993. [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

  1. Colour variation in Costasiella usagi [1]
    From: C. Carlson & P. Hoff, January 15, 2004
  2. Colour variation in Costasiella usagi [2]
    From: C. Carlson & P. Hoff, January 15, 2004
  3. Costasiella sp. 4 is C. usagi
    From: Clay & Patty Jo, January 12, 2004
  4. Costasiella sp. 4 from Lizard Island, Qld.
    From: Nils Anthes, January 10, 2004

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