Taxonomic and Phylogenetic Revision of the Family Chiasmodontidae (Perciformes: Acanthomorpha)

Abstract

The family Chiasmodontidae, commonly known as swallowers, comprises four genera and 33 species distributed in the meso and bathypelagic regions of the Atlantic, Pacific, Indian and Southern Oceans. The species of Chiasmodon and Pseudoscopelus have disjunct distribution, and those of Dysalotus and Kali, wide distributions. The genus Chiasmodon is composed of seven species, two of them new: C. niger; C. subniger; C. braueri; C. microcephalus; C. pluriradiatus; C. asper n. sp.; and C. harteli n. sp. Pseudoscopelus has 16 species, five of them new: P. scriptus; P. sagamianus; P. altipinnis; P. cephalus; P. obtusifrons; P. scutatus; P. aphos; P. parini; P. astronesthidens; P. australis; P. pierbartus; P. bothrorrhinos n. sp.; P. lavenbergi n. sp.; P. paxtoni n. sp.; P. cordilluminatus, n. sp.; and P. odontoglossum sp. n. Dysalotus has only three species, one new: D. alcocki; D. oligoscolus; and D. acanthobrychos. Kali has seven species, two of them new: K. indica; K. kerberti; K. macrodon; K. macrura; K. parri; K. colubrina, n. sp.; and K. falx, n. sp. The chiasmodontids have several morphologic adaptations related to life in the deep-sea and swallowing of enlarged preys. Those characteristics include the reduction of some bones and muscles, diverse dentition, enlarged mouth, a very distensible stomach and body walls, photophores, and the presence of superficial neuromasts on head and body. One of the most remarkable characteristics is the innumerous superficial neuromasts, which are present in all chiasmodontids. The superficial neuromasts are more concentrated in the head, but are also present on body along the trunk lateral-line canal, on upper and lower lobes of the caudal fin, and dorsal part, anterior and to the first-dorsal fin. The distribution of neuromasts is described, as well as their innervation. A phylogenetic analysis was made based on 161 morphological characters obtained from osteology, myology, lateral line system, dentition and miscellaneous. The monophyly of the Chiasmodontidae is corroborated by 24 synapomorphies. Within the chiasmodontids, two major clades are formed: the Chiasmodon clade is composed of Chiasmodon and Pseudoscopelus, and supported by 18 synapomorphies; and the Kali clade is composed by Dysalotus and Kali, and supported by 22 synapomorphies. The monophyly of the genus Chiasmodon is supported by 16 synapomorphies; Pseudoscopelus, by 12 synapomorphies; Dysalotus, by 18 synapomorphies; and Kali, by 23 synapomorphies.