Costasiella usagi

Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Order: Sacoglossa
Family: Costasiellidae
Genus: Costasiella
Species: Costasiella usagi

Costasiella usagi is a sacoglossan, or sap-sucking sea slug, and a close relative of the famous leaf sheep. Its name comes from the Japanese word for rabbit, a nod to its long, ear-like rhinophores.

It is only a few millimetres long, with a body covered in pale whitish-green cerata and dark rhinophores. Like other sacoglossans it is not a true nudibranch, even though it looks like one.

It feeds on Avrainvillea algae, piercing the cells and sucking out the contents. Look for it on clumps of this fan-shaped green alga on shallow sand and rubble.

This is a slug for patient macro photographers. A strong diopter or super macro lens helps, and spotting it is much easier with a dive guide who knows its algae.

It appears on page 342 of Nudibranchs of the Philippines.

Get our entire Nudibranchs of the Philippines book.