In general, there is such skeletal similarity between the 

 •pecies that for most practical purposes it can be truly 

 said that to see the skeleton of one species of Canthi- 

 gaster is to have seen them all, which is decidedly not the 

 case with other genera of tetraodontids with similar 

 numbers of species. 



Until recently I had thought that a goodly number of 

 these monotonously similar features of the species of 

 Canthigaster were not shared by any tetraodontids and 

 that Canthigaster could with good justification be recog- 

 nized as familially distinct from the Tetraodontidae. But 

 the skeletal structure of one relatively specialized tetra- 

 odontid examined recently, and, to a lesser extent, that 

 of a few other species related to it, shows so many 

 similarities to Canthigaster that I am forced to the con- 

 clusion that they share a close common ancestry. From 

 this point of view, Canthigaster seems to me to merit 

 only subfamilial recognition on the basis of the 

 anatomical differences between it and the other tetra- 

 odontids which remain after consideration of the struc- 

 ture of Carinotetraodon lorteti, and its relatives. 



Recently described as Tetraodon somphongsi 

 (Klausewitz, April 1957a and 1957b) and immediately 

 thereafter as Carinotetraodon chlupatyi (Benl, July 

 1957; Benl and Chlupaty 1957), based on specimens from 

 fresh water in Thailand, Dekkers (1975) has shown that 

 the proper specific name is lorteti Tirant 1885. Benl 

 (1959) suggested that the species be retained in the genus 

 Carinotetraodon since it differed from all other tetra- 

 odontids {Canthigaster being considered familially dis- 

 tinct) in being able to raise up a large fold of skin in the 

 midline both dorsally and ventrally, just as in Canthi- 

 gaster. It was believed that such behavioral and 

 anatomical skin changes would probably indicate other, 

 more internal, differences between somphongsi and the 

 other tetraodontids. Tyler (1978) has reviewed the grow- 

 ing aquarium literature on lorteti and the history of its 

 name. 



Because of its moderate tubelike nasal apparatus with 

 a single rounded nostril, Carinotetraodon lorteti 

 otherwise would have to be accommodated in Mono- 

 treta. In fact, on the basis of its coloration and external 

 morphometries, lorteti seems to be most closely related 

 to M. caria (Hamilton-Buchanan), but lorteti is suffi- 

 ciently distinct from the four species of Monotreta ex- 

 amined (cutcutia, which is the type-species, palem- 

 bangensis, leiurus, and gularis) to warrant its retention 

 in Carinotetraodon. 



Regardless of its nomenclature, C. lorteti shares with 

 Canthigaster not only the ability to lift up a ridge of skin 

 dorsally and ventrally along the midline, but a number of 

 internal features as well. The vertebral column in 

 Carinotetraodon is highly arched and almost exactly 

 similar in configuration to that of Canthigaster. The first 

 three vertebrae have bifid neural spines and well- 

 developed haemal spines which do not completely 

 enclose the haemal canal, while the fourth vertebra has 

 the neural spine bifurcate anteriorly, and a large haemal 

 spine, although the flattened region of the spine does not 

 form a distinctive posterior lobe as in Canthigaster. The 



haemal spines of the fifth and subsequent vertebrae are 

 as well developed as in Canthigaster, but again they do 

 not have distinctive posterior lobes. The neural spine of 

 the fourth vertebra is shorter than in Canthigaster, that 

 of the fifth similar to Canthigaster and that of the sixth 

 longer. The long neural spine of the seventh vertebra, 

 supporting the anterior edge of the first basal pterygio- 

 phore, and the succeeding neural spines until the anti- 

 penultimate, are also long shafts, just as in Canthi- 

 gaster, and the basal pterygiophores of the dorsal fin are 

 accommodated between the neural spines of the 7th to 

 11th vertebrae in both genera. However, even though 

 both genera possess a specialized reduced number of 17 

 vertebrae, there are eight abdominal in Canthigaster and 

 only seven in Carinotetraodon. In both genera there are 

 seven vertebrae with neural spines anterior to the first 

 basal pterygiophore of the dorsal fin and seven with 

 neural spines posterior to the last basal pterygiophore. 

 The caudal fin supporting skeleton, and, in general, the 

 last three vertebrae, are highly similar in both genera. 

 The anal fin basal pterygiophores are closely supported 

 basally primarily by the haemal spines of the first three 

 caudal vertebrae, with secondary assistance from that of 

 the fourth, in both genera. Although the number of basal 

 pterygiophores in the dorsal (12) and anal (9) fins of 

 Carinotetraodon is greater than in Canthigaster (usually 

 8 or 9 dorsal and 5 anal), the first basal pterygiophores of 

 both fins in Canthigaster are enormously larger than the 

 others and could represent fusion products of what are 

 the first few pterygiophores in these fins in Carinotetra- 

 odon. 



The similarities between Carinotetraodon and Canthi- 

 gaster in the skull are less extensive than in the vertebral 

 column, but are of phylogenetic interest. In Carino- 

 tetraodon the frontal does not have a pair of postero- 

 lateral processes whose distal ends meet or closely ap- 

 proach one another to partially enclose the muscle to the 

 operculum, one of the most characteristic features of 

 Canthigaster, but a perhaps functionally somewhat 

 similar arrangement is formed by the sphenotic of 

 Carinotetraodon. The sphenotic in Carinotetraodon is 

 broadly present on the dorsal surface of the skull, with an 

 anterolateral wing excluding the posterolateral edge of 

 the frontal from the upper rear margin of the orbit, and, 

 more importantly to the present discussion, a postero- 

 lateral wing prominently projecting out from the lateral 

 surface of the skull, a feature found in none of the other 

 tetraodontids examined. The space between the antero- 

 lateral and posterolateral wings of the sphenotic of 

 Carinotetraodon would seem to correspond to that 

 enclosed by the posterolateral wings of the frontal of 

 Canthigaster. It is suggested here that the condition such 

 as found in Carinotetraodon could have given rise to than 

 in Canthigaster by the gradual posterolateral expansion 

 of the frontals overlying first the anterolateral wing of the 

 sphenotic, which would become reduced in size and 

 eliminated eventually, and then overlying the postero- 

 lateral wing of the sphenotic, which likewise would be 

 eliminated eventually as the frontal took over its suppor- 

 tive function, leaving only a small portion of the 



