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This species has been observed on Mayotte and Madagascar Islands

Order : Sacoglossa Superfamily : Limapontioidea Family : Costasiellidae Distribution : Probably Indo-West Pacific Maximal size : 12 mm Abundance : Species characteristics : The overall body colour is translucent white with fine white speckling towards the front which also features on the quite long, simple rhinophores The cerata down each side of the body which come together at the posterior end are quite distinctive with black digestive gland and sub-terminal orange internal areas and blue tips.  Two small eye spots are visible close together behind the rhinophores and there is a larger black spot further back on the notum
	Showing species characteristics...	Photo Philibert Bidgrain Mayotte, Mtsanga Tanaraki, less 1 m, 24 July 2010, size : 10-12 mm

See more about : Sightening and mating periods

Remarks :

Identification confirmed by Kathe Jensen
      " I am mostly inclined to agreeing with the Costasiella placement ... your Costasiella sp has long stalks to the cerata with unbranched tubule of digestive gland, and that the dark lobules of the digestive gland (characteristic of other species of Costasiella as well) occur only in the outer part of the cerata. It certainly is an interesting little "feller", and I look forwards to hearing of anybody finding it on an identifiable alga (apparently nobody has found it on Avrainvillea , which is the most common food for this genus)"
    According Bill Rudman : "The consensus seems to agree that it is a sacoglossan, and the close set eyes suggest a species of Costasiella. Points of importance are grooved rhinophores, the eyes close together, the "melanin gland" (black spot behind the eyes and in front of the pericardial sac)"
    Under the name of Stiliger sp. 2 in NSSI, Nudibranch & Sea Slug Identification, Indo-Pacific, Gosliner, Valdés & Behrens, 2015

Bibliographic data :

The grooved rhinophores are another good clue to its relationships.
    The eyes, so close together in the dorsal midline, behind the rhinophores, is characteristic of Costasiella
    Presence of a black spot behind the eyes and in front of the pericardial sac. Burn (1998) states that species of Costasiella have a "melanin gland" near the anus, in front of the pericardium, just where the black spot occurs in this species

References :

Bill Rudman Seaslug site : Sea Slug Forum : Costasiella ? sp. 2

Other photos of Costasiella sp. 1 :

Alain-Benoît Rassat Madagascar, Nosy bé, 20 m, size : 10 mm

Philibert Bidgrain Mayotte, Mtsanga Tanaraki, less 1 m, 24 July 2010, size : 10-12 mm Presence of a black spot (a) behind the eyes and in front of the pericardial sac (b). Burn (1998) states that species of Costasiella have a "melanin gland" near the anus, in front of the pericardium, just where the black spot occurs in this species

Fabrice Schubert Mayotte, Tanaraki, 3 m, 10 June 2010. The dark lobules (a) of the digestive gland (characteristic of other species of Costasiella as well) occur only in the outer part of the cerata.

Philibert Bidgrain Mayotte, Mtsanga Tanaraki, less 1 m, 24 July 2010, size : 12-15 mm Crawling on a sandy subtrate during the day... Presence of a black spot (a) behind the eyes and in front of the pericardial sac (b). Burn (1998) states that species of Costasiella have a "melanin gland" near the anus, in front of the pericardium, just where the black spot occurs in this species

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