The threefin blenny Enneapterygius hemimelas is widespread throughout the Pacific Ocean.
Adults are found in a variety of reef habitats, especially on reef slabs in tide pools and surf-blown reef margins.
This species also occurs in intertidal areas and is usually associated with coral rock outcrops and coral reef lagoons.
Eggs are hemispherical and covered with numerous sticky filaments that anchor them in the algae at nesting sites.
Larvae are planktonic and are found primarily in shallow, nearshore waters.
Males have a dark underside of the head and their bodies darken abruptly toward the rear, occasionally with alternating broad dark and light bands.
Adults can be identified by the greenish tail, and the color usually extends well onto the body.
Adult males have two broad black bands below the third dorsal fin attachment and caudal peduncle, with the two bands joined ventrally; the posterior portion of the anal fin is black in adult males of the threefin blenny, the caudal fin attachment is white, and pectoral and pelvic fins and body are orange in adult males.
Females are much less color conspicuous, see photo, they are well adapted to their habitat with their body pattern.
Enneapterygius fuligicauda Fowler, 1946
Enneapterygius macrobrachium Fowler, 1946
Tripterigium hemimelas Kner & Steindachner, 1867
Tripterygion fuligicauda (Fowler, 1946)
Tripterygion hemimelas (Kner & Steindachner, 1867)
Tripterygion macrobrachium (Fowler, 1946)
Tripterygium hemimelas Kner & Steindachner, 1867