Costasiella vegae is common in the Marshalls, where it is found almost exclusively on clumps of what appears to be the alga Avrainvillea amadelpha. This species of algae grows in fairly large solitary clumps on the sandy lagoon slope at depths of 6 to 15m, so that is where C. vegae is found as well. There may be many specimens and numerous white spiral egg masses on a single algae clump. Specimens we have examined ranged in length from about 3 to 6mm. In the first photo below, the close-set black eyes are readily visible between tentacles near the bottom of the frame. There seems to still be considerable uncertainty about the exact identities of some tiny members of this variable family. Our ID is based on photos and a description in the Sea Slug Forum.
The animals below is surrounded by several egg masses and what appear to be "scars" on the algae left by former egg masses.
The animal below is a different specimen, found on 7 July 2008 on Avraivillea growing on a sandy lagoon reef at about 7m depth. Several specimens were observed along with a crowded group of egg masses deposited on the algae.
The specimen below was observed on 25 February 2008.
Created 5 November 2007
Updated 24 January 2020