Lives in an abandoned worm tube in rubble and displays by shooting out and raising a dorsal fin as tall as the fish, several times a minute.
To about 7 cm. Elongate with a short blunt head and a steep front profile, a branched tentacle at the nostril and a short three-tipped one over the eye. Males are tan with nine or ten dark brown spots along the flank and an enormous sail-like first dorsal fin whose fourth to sixth spines are the longest, often with a small blue spot at the base of the first spine. Females are light tan with about thirteen brown blotches along the flank and pale saddles on the back, and have no sail.
Two related sailfin blennies are separated on the fin: one has two eyespots on the dorsal fin, and the shape of the sail differs.
It lives in an empty worm tube, a vermetid shell or a hole in coral rubble on sand and rubble bottoms at channel edges, between about 1 and 35 m, with only its head showing. The reason divers look for it is the male’s display: he launches vertically out of the hole with the sail fully raised, turns black except for the soft dorsal fin and tail, and drops back in, over and over.
A 2024 study found that this name covers several cryptic species, each restricted to a region, so Florida, Bahamas and Caribbean sailfin blennies may not all be the same fish. Nothing has been formally split yet.
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.