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Nudibranch - Costasiella usagi
This Costasiella usagi Nudibranch is tiny in size, around 3-4 mm, they probably gets to max of 5 mm.
This one is a bit different from the other Costasiella species ie. Costasiella kuroshimae, the cerata are mostly white or light green in colour. However, both species can be found in the same location/dive site and on the same food source algae. However, I haven't seen them on the same piece of algae leaf yet, not surprised if they co-exist on the same host of algae which is usually just around 2-3 cm in diameter size.
The tiny 2 black dots are their eyes, which are very primitive, only able to sense light.
Costasiella usagi is a species of sacoglossan sea slug, a shell-less marine opisthobranch gastropod mollusk in the family Costasiellidae. It has the ability to incorporate chloroplasts from the algae it feeds on into its body and use them to do photosynthesis.
