Costasiella usagi Ichikawa, 1993

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This species has been observed on Mayotte Island


Order : Sacoglossa
Superfamily : Limapontioidea
Family : Costasiellidae
Distribution : Indo-West Pacific
Maximal size : 6 mm
Abundance :


Species characteristics :

The presence of longitudinal white lines on the green gray or black cerata is distinctive for this species.

Usually the cerata possess a white end and a black tip.

The head and the long and pointed tail are not pigmented

The rhinophores range from completely black to black edged.

costasiella usagi
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Photo Eva Fontaine
Mayotte, Mtsanga M'boueanatsa, less 1 m, 30 July 2010, size 5 : mm

See more about : Sightening and mating periods

Remarks :

Identification confirmed by Kathe Jensen
    Synonymous : (according Worms)
               - No other name

Bibliographic data :

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 bear 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."
    As in other Costasiella, the large eyes lie close together between the bases of the simple rolled rhinophores
    The anterior corners of the foot are tentaculiform and the tail is long and pointed.
    Found in association with Avrainvillea sp (green algae with a post like "stalk" and a flattened plate-like "leaf") in sandy patches between reefs.

References :

Bill Rudman Seaslug site : Sea Slug Forum : Costasiella usagi
   Nudipixel Costasiella usagi

Publications :

Ichikawa, M. (1993) Saccoglossa (Opisthobranchia) from the Ryukyu Islands. Publications of the Seto Marine Biological Laboratory, 36 : 119-139
    Jensen, K.R. (2007). Biogeography of the Sacoglossa (Mollusca, Opisthobranchia). Bonner Zoologische Beiträge. 55: 255281.

Other photos of Costasiella usagi :


Photo Eva Fontaine

Mayotte, Mtsanga M'boueanatsa, less 1 m, 30 July 2010, size 5 : mm for the larger

Two specimens found in association with Avrainvillea sp (green algae with a post like "stalk" and a flattened plate-like "leaf") in sandy patches between reefs.


 More photos from Indian Ocean