Fan bellied leatherjacket fish

Filefish family - oddly-shaped fish often with dazzlingly cryptic patterns. Deeply keeled bodies give a false impression of size when these fish are viewed facing the flanks. Filefish have soft, simple fins with comparatively small pectoral fins and truncated, fan-shaped tail fins; a slender, retractable spine crowns the head. Although there are usually two of these spines, the second spine is greatly reduced, being used only to lock the first spine in the erect position; this explains the family name Monacanthidae, from the Greek monos meaning "one" and akantha meaning "thorn". Some species also have recurved spines on the base of the tail (caudal peduncle).