A transparent nudibranch flattened into a fish shape, with no foot and a branched gut showing through.
A sea slug that looks like a small transparent fish. The body is flattened from side to side and drawn out to a pointed tail, there are two slender rhinophores at the head end and no foot at all, and the branched digestive gland shows through the body wall as a fine amber or brown tree. It swims by beating the whole body from side to side and is bioluminescent when disturbed, which is occasionally what draws attention to one.
Phylliroe feeds on hydromedusae. Small individuals are found attached to a single medusa, riding it and consuming it over time, and leave when it is gone; larger animals take gelatinous prey in open water. The pelagic nudibranch Cephalopyge trematoides, which has its own entry, is a related open-water slug, but it keeps a rounded slug outline rather than a compressed leaf shape and feeds on siphonophores.
Recorded from warm seas worldwide, and a regular though uncommon subject at the blackwater sites run in Indonesia and the Philippines. Species-level identification rests on internal characters and on details of the digestive gland, so records here are kept at the genus. The transparency means a frame usually resolves the gut and the rhinophores and infers the rest of the outline from a rim of refraction.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
