parietals, nasals, or infraorbitals, and usually no lower ribs; posttemporal, if present, simple and fused with pterotic of skull; hyomandibular and palatine firmly attached to skull; gill openings restricted; maxilla usually firmly united or fused with premaxilla; scales usually modified as spines, shields, or plates; lateral line present or absent, sometimes multiple; swim bladder present except in molids; 16-30 vertebrae.
Tetraodontiformes can produce sounds by grinding the jaw teeth or the pharyngeal teeth or by vibrating the swim bladder. The stomach of some tetraodontiforms is highly modified to allow inflation to an enormous size. Fishes with this ability belong to the families Tetraodontidae, Diodontidae, and, where it is less well developed, Triodontidae; they are popularly called "puffers." Inflation is caused by gulping water into a ventral diverticulum of the stomach when the fish is frightened or annoyed. Deflation occurs by
expelling the water. If the fish is removed from the water, inflation can occur with air. The triodontid and most balistids have another mechanism for slightly enlarging their bodies. They do this by expanding a ventral flap supported by a large movable pelvic bone.
The present classification, changed above the family level from Nelson (1994), is based on the cladistic study of fossil and extant taxa by Santini and Tyler (2003) (extensive information on the finely preserved Monte Bloca fossils was given in Tyler and Santini, 2002). There are many changes in our understanding of relationships between families.
The sister group of this order is the subject of considerable uncertainty, and more studies are needed on this problem. Some studies have concluded that all or some tetraodontiforms are related to acanthuroids, zeiforms, or caproids (see above under order Perciformes, and suborder Caproidei, for brief discussion). I have retained the Tetraodontiformes in their classical postperciform position pending further studies.
Nine families with approximately 101 genera and 357 extant species. About 14 species occur only in freshwater, and another eight or so may be found in freshwater.
f Suborder Plectocretacicoidei. Three Upper Cretaceous families, Cretatriacanthidae, Plectocretacicidae, and Protriacanthidae, are recognized by Tyler and Sorbini (1996) and Santini and Tyler (2003).
Suborder Triacanthodoidei. Synapomorphies were given in Santini and Tyler (2003). The one family shares the following primitive features with the Triacanthidae, formerly placed in this suborder: pelvic fin spine large and able to be locked into position; upper jaw slightly protractile (ascending process of premaxilla well developed); pelvic fin with one large spine and up to two soft rays; dorsal fin usually with six spines; caudal fin with 12 principal rays; 2-6 separate hypurals; 20 vertebrae.
Family TRIACANTHODIDAE (503)—spikefishes. Marine; deepwater benthic; tropical and subtropical western Atlantic and Indo-Pacific.
Dorsal fin rays 12-18; anal fin rays 11-16; caudal fin rounded to truncate.
Two subfamilies, 11 genera, and about 21 species (Tyler, 1997; Matsuura in Carpenter and Niem, 2001).
Subfamily Hollardinae. Western Atlantic, one species in Hawaii.
Two genera, Hollardia and Parahollardia,, with five species. The orthography of the subfamily name is changed from Nelson (1994) following Santini and Tyler (2003).
Subfamily Triacanthodinae. Indo-Pacific, one species in western Atlantic.
Nine genera, Atrophacanthus, Bathyphylax, Halimochirurgus, Johnsonina, Macrorhamphosodes, Mephisto, Paratriacanthodes, Triacanthodes, and Tydemania, with 16 species.
Suborder Balistoidei (Sclerodermi). Frontals extending far anterior to articulation between lateral ethmoid and ethmoid.
Five fossil families were recognized by Santini and Tyler (2003), Moclaybalistidae, Bolcabalistidae, Eospinidae, Spinacanthidae, and Protobalistidae (the last two were placed in the superfamily Ostracioidea). Four families, 61 genera, and 182 species.
Superfamily Triacanthoidea. One family.
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