Dibrachichthys

Dibrachichthys is a monospecific genus belonging to the family Tetrabrachiidae, the four-armed frogfishes. The only species in the genus is Dibrachichthys melanurus, the twoarm humpback anglerfish, which is found in the eastern Indian and western Pacific Oceans.

Taxonomy
Dibrachichthys was first proposed as a genus in 2009 by Theodore Wells Pietsch III, Jeffrey W. Johnson and Rachel J. Arnold when they described Dibrachichthys melanurus. The type locality of the new species was given as 11°06.9'S, 142°51.9'E, northeast of Ussher Point on the Cape York Peninsula in Queensland. This genus is one of two genera, both monotypic, in the family Tetrabrachiidae. The Tetrabrachiidae is classified within the suborder Antennarioidei within the order Lophiiformes, the anglerfishes.

Etymology
Dibrachichthys combines di, meaning "two", brachium, meaning "arm", and ichthys, which means "fish". This is an allusion to the possession f a single undivided pectoral fin on each side, in contrast to the split pectoral fins of the only other species in the Tetrabrachiidae, Tetrabrachium ocellatum which has its pectoral fins divided. The specific name melanurus means "blacktail", and is a reference to the black bar on the base of the caudal fin.

Description
Dibrachichthys has its dorsal fin supported by 14 or 15 soft rays and the anal fin is supported by between 8 and 10 soft rays. It is very similar to ''T.. ocellatum but has a single, non divided pectoral fin on each side instead of T. ocellatum's'' split pectoral fins. The cranium is markedly wider than that of T. ocellatum and some of the skull bones form a horizontal tube-like structure t the front of each eye. The eyes are set in a deep semi-circular protective cavity and there is adeep depression in the middle of the cranium. The coloration is different too with a dark inside of the mouth, a dark bar on the back just below the base of the dorsal fin and a dark bar on the base of the caudal fin. Males have a maximum published standard length of 5.7 cm, while females are slightly smaller with a maximum published standard length of 5.6 cm.

Distribution and habitat
Dibrachichthys is found in the Australia, Papua New Guinea and Indonesia. In Australia it is found around the north from southwest of Dongara in Western Australia to east of Yeppoon in the Capricorn Islandsoff Queensland]. It also occurs in the Aru Islands of Indonesia and the Torres Strait off Papua New Guinea. This is a demersal fish found at depths between 5 and 63 m, although two specimens were collected between 128 and 146 m, on soft substrates of sand and mud in nearsgore waters and in areas with rubble on the continental shelf.

Biology
Dibrachichthys appears to be solitary and individuals are widely dispersed. The eggs are laid by the female in tight clusters bound with filaments. The females have the tips of some of the dorsal fin rays free of the membrane and in T. ocellatum, and probably in this species, the filaments of the egg cluster entangle round these tips and are kept their until they hatch.