Opisthobranch of the Week Data
Costasiella sp. 1 is considered to be uncommon, sixteen specimens have been collected and all were found between 130ft ~ 185ft at the Seragaki dive site on Okinawa. The animals were all collected from an area of mixed coral rubble and sand with numerous thallophytes (reds, greens, and browns) in the general area. These small costasiellids were found later at home in a sorting dish which held a large sample of mixed algae, along with cnidarians, poriferans, and other invertebrates. No particular alga was noted to be associated with these small animals.
It could well be that Costasiella sp. 1 is an undescribed species of sacoglossan. Kathe Jensen (2002) reporting in the Sea Slug Forum, mentions that she has a series of Costasiella species from Singapore. She apparently at one time was to have described these along with Jon Sigurdsson, but that the paper didn't get started due to her following statement:
" . . . this awful paper by Ichikawa appeared. In this paper she describes 6 species of Costasiella based on photos and serial sections. There are so many characters not mentioned in these descriptions that it is impossible to compare these species with others."
In looking through the Ichikawa (1993) paper, Costasiella sp. 1 is not one of her species. The brown or reddish brown pigmented head with an obvious blue pigment spot posterior to the relatively large eyes, the iridescent blue spots on the rhinophores, cerata, and tail seem to be consistent with the other Okinawa-collected individuals.