Bathynectes.—Body produced into a long tapering tail, without caudal. Mouth very wide, villiform teeth in the jaws, on the vomer and palatine bones. Barbel none. Ventral fins reduced to simple or bifid filaments, placed close together, and near to the humeral symphysis. Gill-membranes not united; gill-laminæ remarkably short. Bones of the head soft and cavernous; operculum with a very feeble spine above.
Deep-sea fishes, inhabiting depths varying from 1000 to 2500 fathoms. Three species are known, the largest specimen obtained being seventeen inches long.
Fig. 251.—Acanthonus armatus.
Acanthonus.—Head large and thick, armed in front and on the opercles with strong spines; trunk very short, the vent being below the pectoral; tail thin, strongly compressed, tapering, without caudal. Eye small. Mouth very wide; villiform teeth in the jaws, on the vomer and palatine bones. Barbel none. Ventrals reduced to simple filaments placed close together on the humeral symphysis. Scales extremely small. Bones of the head soft.
Only two specimens, thirteen inches long, of this remarkable deep-sea form have been obtained, at a depth of 1075 fathoms, in the Indian Ocean.
Typhlonus.—Head large, compressed, with most of the bones in a cartilaginous condition; the superficial bones with large muciferous cavities, not armed. Snout a thick protuberance projecting beyond the mouth, which is rather small and inferior. Trunk very short, the vent being below the pectoral; tail thin, strongly compressed, tapering, without separate caudal. Eye externally not visible. Villiform teeth in the jaws, on the vomer and palatine bones. Barbel none. Scales thin, deciduous, small.
Also of this deep-sea fish two specimens only are known, 10 inches long, from a depth of 2200 fathoms in the Western Pacific.
Aphyonus.—Head, body, and tapering tail strongly compressed, enveloped in a thin, scaleless, loose skin. Vent far behind the pectoral. Snout swollen, projecting beyond the wide mouth. No teeth in the upper jaw, small ones in the lower. No externally visible eye. Barbel none. Head covered with a system of wide muciferous channels, the dermal bones being almost membranaceous, whilst the others are in a semi-cartilaginous condition. Notochord persistent, but with a superficial indication of vertebral segments.
