Wikipedia
The blennioid family Chaenopsidae includes the pike-blennies, tube-blennies, and flagblennies, all perciform marine fish. The family is strictly tropical, ranging from North to South America. Members are also present in waters off Japan, Taiwan and Korea. Fourteen genera and 90 species are represented, the largest being the sarcastic fringehead, Neoclinus blanchardi, at in length; most are much smaller, and the group includes perhaps the smallest of all vertebrates, Acanthemblemaria paula, measuring just long as an adult.
With highly compressed bodies, some may be so elongated as to appear eel-like; chaenopsids are scaleless and lack lateral lines. Their heads are rough and may be armed with spines. There may be 17 to 28 spines in the dorsal fin, with two in the anal fin.
The habit of taking up home in abandoned worm tubes has earned some species in this family the name "tube-blenny". Many will also inhabit empty clam shells, which also serve as nesting sites; males are known to guard the brood. Some species have dorsal fins which are significantly higher towards the head, explaining the moniker "flagblenny". Crustaceans make up the bulk of the chaenopsid diet.
At least one species found in the Caribbean is known to form a symbiotic relationship with stony coral.