THE OSTEOLOGY OF FAMILY CHACIDAE: 1. THE SKULL OF CHACA CHACA (HAMILTON)

SUMMARY 1. Support is cited for the establishment of a separate family, Chacidae comprising the monotypic genus Chaca based on the obtained osteological data. 2. The osteological characterisation of family Chacidae as well as genus Chaca is provided: very broad and depressed skull; very wide mouth gape bounded by unequal jaws; quite broad ethmoid with long and stout cornua; strongly projecting lateral ethmoid; toothless but conspicuous vomer; forked lachrymal; suborbitals lacking; very much reduced nasals; occipital process peculiarly modified. Movable premaxillae, quite large and broad palatine; minute ectopterygoid; hyomandibula solely sustained from the sphenotic; single hypohyal; eight branchiostegal rays; no basibranchials and gill-rakers and single pharyngobranchial. 3. The relationship of the family Chacidae with the Siluridae, Plotosidae, Bagridae and Sisoridae on the evidence of osteology is discussed and osteological support is found for its close affinity with the Sisoridae. 4. A brief discussi...