Marine fishes from the Indian and Western Pacific Oceans. Ten species, referable to three genera: Triacanthus, Triacanthodes, Halimochirurgus. The latter, remarkable for its long, tube-like snout, is the only deep-sea form of this Sub-order; it was recently discovered in the Gulf of Manaar, at a depth of 143 fathoms. Fossil genera are Acanthopleurus, Oligocene, and Spinacanthus, Eocene.
Fam. 2. Triodontidae.—Praemaxillaries not protractile, firmly united to the maxillaries; teeth coalescent into a beak, the upper jaw divided by a median suture, the lower simple. Praecaudal vertebrae with or without parapophyses; epipleurals present. No spinous dorsal fin. No ventral fins. Abdomen with a dilatable sac, kept expanded by the very long movable pelvis. Body covered with small, spiny, subimbricate, bony laminae. Vertebrae 20.
A single species, the curious Triodon bursarius of the Indian Ocean and Archipelago.
Fig. 437.—Monacanthus, sp., with enlarged views of dorsal scales (b) and ventral spine (c).
Fam. 3. Balistidae.—Praemaxillaries not protractile, firmly united to the praemaxillaries; teeth incisor-like; palatine movably articulated with ectopterygoid, or entirely free from it. Gills 4. Praecaudal vertebrae with well-developed parapophyses, to which epipleurals are attached. Spinous dorsal fin with 1 to 3 spines. Ventral fins, if present, represented by a single short rough spine at the end of the long, movable pelvis. Body covered with juxtaposed movable scutes or with minute rough scales.
About 100 species are known from the tropical and warm seas, one species (Balistes capriscus) occasionally wandering as far north as the south coast of England. Genera: Balistes, Monacanthus, Paraluteres, Pseudaluteres, Pseudomonacanthus, Aluteres, Psilocephalus. The Oligocene genus Acanthoderma is closely allied to Balistes.
The "File-Fishes" or "Trigger-Fishes" (Balistes), the largest species of which grow to nearly 3 feet, have a powerful dentition, which enables them to break off pieces of corals, on which they feed, and to bore holes in the hard shells of Mollusca in order to extract the soft parts; they are themselves well protected by a mail of hard, rhomboidal scales. The herbivorous Monacanthus is less favoured in this respect, the rough scales being so small as to give the skin a velvety appearance.
Psilocephalus differs from Monacanthus in its very elongate head and body, the very feeble dorsal spine, the presence of a mental barbel, and its more numerous vertebrae (29 or 30 instead of 18 to 21). The flesh of many of these fishes is poisonous.[[760]] The drumming sounds produced by Balistes have been described by Möbius.[[761]]
Fam. 4. Ostraciontidae.—Praemaxillaries not protractile, firmly united to the praemaxillaries; teeth incisor-like; palatine immovable. Gills 4. Praecaudal vertebrae with very feeble parapophyses and no epipleurals. No spinous dorsal fin. Clavicles, coracoids, and post-clavicles much expanded. No ventral fins. Body encased in a carapace formed of large, juxtaposed, mostly hexagonal bony plates. Vertebrae 14 to 16.