CHAPTER XXIII

THE SQUAMIPINNES

=The Squamipinnes.=—Very closely allied to the _Percomorphi_ is the great group called _Squamipinnes_ (_squama_, scale; _pinna_, fin) by Cuvier and _Epelasmia_ by Cope. With a general agreement with the _Percomorphi_, it is distinguished by the more or less complete soldering of the post-temporal with the cranium. In the more specialized forms we find also a soldering of the elements of the upper jaw, and a progressive reduction in the size of the gill-opening. The ventral fin retains its thoracic insertion, and, as in the perch mackerel-like forms, it has one spine and five rays, never any more. The ventral fins are occasionally lost in the adult, as in the _Stromateidæ_, or they may lose part of their rays. The name _Squamipinnes_ refers to the scaly fins, the typical species having the soft rays of dorsal, anal, and caudal, and sometimes of other fins densely covered with small scales. In various aberrant forms these scales are absent. The name _Epelasmia_ (ἔπι, above; ἐλάσμος, plate) refers to the thin upper pharyngeals characteristic of certain forms. The transition from this group to the _Sclerodermi_ is very clear and very gradual. The _Squamipinnes_, _Sclerodermi_, _Ostracodermi_, and _Gymnodontes_ form a continuous degenerating series. On the other hand the less specialized _Squamipinnes_ approach very closely to forms already considered. The _Antigoniidæ_ are of uncertain affinities, possibly derived from such forms as _Histiopteridæ_, while _Platax_ show considerable resemblance to scaly-finned fishes like the _Kyphosidæ_ and _Stromateidæ_. The _Scorpididæ_ seem intermediate between _Stromateidæ_ and _Platacidæ_. In such offshoots from _Scombroidei_ or _Percoidei_ the group doubtless had its origin.

We may begin the series with some forms which are of doubtful affinity and more or less intermediate between the _Squamipinnes_ and the more primitive _Percomorphi_.

=The Scorpididæ.=—This family has the general appearance of _Platax_ and _Ilarches_, but the teeth are not brush-like, and the post-temporal is free from the skull as in perch-like fishes. The species inhabit the Pacific. _Scorpis georgianus_ is a food-fish of Australia, with the body oblong. _Monodactylus argenteus_, the toto of Samoa, is almost orbicular in form, while _Psettus sebæ_ is twice as deep as long, the deepest-bodied of all fishes in proportion to its length.

=The Boarfishes: Antigoniidæ.=—The boarfishes (_Antigoniidæ_) are characterized by a very deep body covered with rough scales, the post-temporal, as in the _Chætodontidæ_ and the _Zeidæ_, being adnate to the skull.

These fishes bear some resemblance to _Zeus_, but there is no evidence of close affinity nor is it clear that they are related to the _Chætodontidæ_. _Capros aper_, the boarfish, is common in southern Europe, reaching a length of less than a foot, the protractile mouth suggesting that of a pig. The diamond-fishes, _Antigonia_, are deeper than long and strongly compressed, the body being covered with roughish scales. The color is salmon-red and the species live just below the depths ordinarily explored by fishermen. _Antigonia capros_ is found at Madeira and in the West Indies, _Antigonia steindachneri_ about Hawaii and in Japan, while the smaller _Antigonia rubescens_ is abundant in the Japanese bays at a depth reached by the dredge. An extinct genus, _Proantigonia_ from the Miocene is said to connect _Antigonia_ with _Capros_.

=The Arches: Toxotidæ.=—The archers, _Toxotidæ_, have the body compressed, the snout produced, and the dorsal fin with but five spines. The skeleton differs widely from that of _Chætodon_ and the family should perhaps rather find its place among the percoids. _Toxotes jaculatrix_ is found in the East Indies. The name alludes to its supposed habit of catching insects by shooting drops of water at them through its long mouth.

=The Ephippidæ.=—With the typical _Squamipinnes_, the teeth become very slender, crowded in brush-like bands. The least specialized family is that of _Ephippidæ_, characterized by the presence of four anal spines and a recumbent spine before the dorsal. The principal genus, _Ephippus_ (_Scatophagus_), is represented by _Ephippus argus_, a small, bass-like fish, spotted with black, found in the Indian seas, and ranging northward to Formosa. Species referred to _Ephippus_ (_Scatophagus_) are recorded from the Italian Eocene of Monte Bolca, where a species of _Toxotes_ has been also found.

=The Spadefishes: Ilarchidæ.=—In the _Ilarchidæ_ the dorsal is divided into two fins, the spinous part being free from scales. In various regards the species are intermediate between ordinary perch-like forms and the chætodonts. In these fishes the body is very deep and, with the soft fins, closely covered with roughish scales. In _Ilarches_ (_Ephippus_), represented by _Ilarches orbis_ of the Indian seas, these scales are relatively large. This species is a common food-fish from India to Formosa.

In the American genus, _Chætodipterus_, the scales are quite small. The spadefish (_Chætodipterus faber_), sometimes called also moonfish or angel-fish, is a large, deep-bodied fish, reaching a length of two feet. It is rather common from Cape Cod to Cuba, and is an excellent pan fish, with finely flavored white flesh. The young are marked by black cross-bands which disappear with age, and in the adult the supraoccipital crest is greatly thickened and the skull otherwise modified. A very similar species, _Chætodipterus zonatus_, occurs on the west coast of Mexico. Species allied to _Chætodipterus_ are fossil in the Italian Eocene. The _Drepanidæ_ of the East Indies are close to the _Ilarchidæ_. _Drepane punctata_ is a large, deep-bodied fish resembling the spadefish but with larger scales.

=The Platacidæ.=—Closely related to the _Ilarchidæ_ is also the East Indian family of _Platacidæ_, remarkable for the very great depth and compression of the body, which is much deeper than long, and the highly elevated dorsal and anal still further emphasize this peculiarity of form. In this group the few dorsal spines are closely attached to the soft rays and the general color is dusky. In the young the body is deeper than in the adult and the ventral fins much more produced. The best-known species is the tsuzume or batfish (_Platax orbicularis_), which ranges from India through the warm current to northern Japan. _Platax teira_, farther south, is very similar. _Platax_ _altissimus_, with a very high dorsal, is a fossil in the Eocene of Monte Bolca.

=The Butterfly-fishes: Chætodontidæ.=—The central family of _Squamipinnes_ is that of the butterfly-fishes or _Chætodontidæ_. In this group the teeth are distinctly brush-like, the mouth small, the dorsal fin continuous and closely scaly, and the ventral fins with one spine and five rays. The species are mostly of small size and brilliant and varied coloration, yellow and black being the leading colors. They vary considerably with age, the young having the posterior free edges of the bones of the head produced, forming a sort of collar. These forms have received the name of _Tholichthys_, but that supposed genus is merely the young of _Chætodon_. The species of _Chætodontidæ_ abound in rock pools and about coral reefs in clear water. They are among the most characteristic forms of these waters and their excessive quickness of movement compensates for their conspicuous coloration. In these confined localities they have, however, few enemies. The broad bodies and spinous fins make them rather difficult for a large fish to swallow. They feed on small crustaceans, worms, and the like. The analogy to the butterfly is a striking one, giving rise to the English name, butterfly-fish, the Spanish mariposa, and the Japanese chochouwo, all having the same meaning. Fossil chætodonts are rather few, _Chætodon pseudorhombus_ of the Pliocene of France, _Holocanthus microcephalus_ and _Pomacanthus subarcuatus_ of the Eocene, being the only species recorded by Zittel.

In the principal genus, _Chætodon_, the colors are especially bright. There is almost always a black bar across the eye, and often black ocelli adorn the fins. This genus is wanting in Europe. _Chætodon capistratus_, _striatus_, and numerous other species are found in the West Indies; _Chætodon humeralis_ and _nigrirostris_ are common on the coast of Mexico. The center of their distribution is in Polynesia and the East Indian Archipelago. _Chætodon reticulatus_, _lineolatus_, _ulietensis_, _ornatissimus_, _ephippion_, _setifer_, and _auriga_ are among the most showy species. Numerous closely related genera are described. In some of these the snout is prolonged into a long tube, bearing the jaws at its end. Of this type are _Chelmo_ in India, _Forcipiger_ in Polynesia, and _Prognathodes_ in the West Indies. _Heniochus_ (_macrolepidotus_) has one dorsal spine greatly elongated. _Microcanthus strigatus_, one of the most widely distributed species, is known by its small scales. _Megaprotodon_ (_triangularis_) has four anal spines instead of three as in the others.

The species of _Holacanthus_, known as angel-fishes, are larger in size, and their colors are still more showy, being often scarlet or blue. In this genus the preopercle is armed with a strong spine, and there are fourteen or more strong spines in the dorsal. This genus has also its center of distribution in the East Indies, whence two species (_septentrionalis_ and _ronin_) with concentric stripes of blue range northward to Japan. _Holacanthus tibicen_, jet-black with one yellow cross-band, is found from the Riu Kiu Islands southward. The angel-fish or isabelita (_Holacanthus ciliaris_), orange-red, sky-blue, and golden, as though gaudily painted, is the best-known species. The vaqueta de dos colores or rock beauty (_Holacanthus bicolor_), half jet-black, half golden, is scarcely less remarkable. Both are excellent food-fishes of the West Indies. _Holacanthus passer_ is a showy inhabitant of the west coast of Mexico. _Holacanthus diacanthus_, orange, barred with blue, is one of the gaudiest inhabitants of the coral reefs of Polynesia. _Holacanthus flavissimus_, golden with some deep-blue markings, and _Holacanthus nicobariensis_, blackish with white circles, are found with other species in the same waters.

The genus _Pomacanthus_ (_Pomacanthodes_) includes American species only, still larger in size and differing from _Holacanthus_ in having nine to eleven spines only in the dorsal fin. The young of _Pomacanthus_ are blackish, crossed by many curved yellow cross-bands, which disappear entirely with age. Three species are known, _Pomacanthus arcuatus_, the black angel, chirivita or portugais, _Pomacanthus paru_, the Indian-fish or paru of the West Indies, and _Pomacanthus zonipectus_, "Mojarra de las Piedras," of the west coast of Mexico. All are good food-fishes, but lacking the brilliant colors of _Holacanthus_ and the fine pattern usual in _Chætodon_.

=The Pygæidæ.=—Between the _Chætodontidæ_ and the _Acanthuridæ_ we would place the extinct family of _Pygæidæ_, of the Eocene. In _Pygæus gigas_ and other species the dorsal spines are strong and numerous; there are 5 to 8 species in the anal fin, the scales are shagreen-like, and the teeth seem coarser than in the _Chætodontidæ_. The tail is apparently unarmed, and the soft dorsal, as in _Chætodon_, is much shorter than the spinous. To this family the Eocene genera, _Aulorhamphus_ (_bolceusis_), with produced snout, and _Apostasis_ (_croaticus_), with long spinous dorsal, probably belong.

=The Moorish Idols: Zanclidæ.=—The family of _Zanclidæ_ includes a single species, the Moorish idol or kihi kihi, _Zanclus canescens_. In this family the scales are reduced to a fine shagreen, and in the adult two bony horns grow out over the eye. The dorsal spines are prolonged in filaments and the color is yellow crossed by bars of black. _Zanclus canescens_ is a very handsome fish with the general appearance and habit of a _Chætodon_, but the form is more exaggerated. It is found throughout Polynesia, from Japan to the off-shore islands of Mexico, and is generally common, though rarely entering rock pools.

_Zanclus eocænus_ is recorded from the Italian Eocene.

=The Tangs: Acanthuridæ.=—In the next family, _Acanthuridæ_, the surgeon-fishes or tangs, the scales remain small and shagreen-like, the body is more elongate, the gill-openings still more restricted, and the teeth are flattened and incisor-like. The pubic bone is more elongate, and in all the species some sort of armature is developed on the side of the tail. The spinous dorsal in all is less developed than the soft dorsal. The species abound in the warm seas, especially about the tide pools, and are used as food. They undergo considerable changes with age, the caudal armature being developed by degrees. Nearly all are dull brown in color, but in some a vivid ornamentation is added. Fossil forms are found from the Eocene and later. Most of these are referable to _Teuthis_ and _Acanthurus_.

The principal genus is _Teuthis_, characterized by the presence on each side of the tail of a sharp, knife-like, movable spine with the point turned forwards and dropping into a sheath. This spine gives these fishes their name of surgeon-fish, doctor-fish, lancet-fish, tang, barbero, etc., and it forms a very effective weapon against fish or man who would seize one of these creatures by the tail. The species have the center of distribution in the East Indies and have not reached Europe. Three species are found in the West Indies. The blue tang (_Teuthis cœruleus_) is chiefly bright blue. The common tang, _Teuthis chirurgus_, is brown with bluish streaks, while a third species, _Teuthis bahianus_, has a forked caudal fin. Very close to this species is _Teuthis crestonis_, of the west coast of Mexico, and both are closely related to _Teuthis matoides_, found from India to Hawaii.

_Teuthis triostegus_, of Japan and Polynesia and the East Indies, is covered with cross-bands alternately black and pale. In Hawaii this is replaced by the very similar _Teuthis sandwichensis_. Many species are found about Hawaii and the other Polynesian Islands. _Teuthis achilles_ has a large blotch of brilliant scarlet on the tail, and _Teuthis olivaceus_ a bright-colored mark on the shoulder. _Teuthis lineatus_, yellow with blue stripes, a showily colored fish of the coral reefs, is often poisonous, its flesh producing ciguatera.

_Zebrasoma_ differs from _Teuthis_ in having but 4 or 5 dorsal spines instead of 10 or 11. In this genus the soft dorsal fin is very high. _Zebrasoma flavescens_, sometimes brown, sometimes bright yellow, is common in Polynesia; _Zebrasoma veliferum_, cross-barred with black, is also common.

_Ctenochætus_ (_strigosus_), unlike the others, is herbivorous and has its teeth loosely implanted in the gums. This species, black with dull orange streaks, was once tabu to the king of Hawaii, who ate it raw, and common people who appropriated it were put to death.

In _Xesurus_ the caudal lancelet is replaced by three or four bony tubercles which have no sharp edge. _Xesurus scalprum_ is common in Japan, and there are three species or more on the west coast of Mexico, _Xesurus punctatus_ and _Xesurus laticlavius_ being most abundant.

In _Prionurus_ (_microlepidotus_) of the tropical Pacific the armature is still more degraded, about six small plates being developed.

In _Acanthurus_ (_Monoceros_, _Naseus_), the unicorn-fish and its relatives, the ventral fins are reduced, having but three soft rays, the caudal spines are very large, blunt, immovable, one placed in front of the other. In most of the species of _Acanthurus_ a long, bony horn grows forward from the cranium above the eye. This is wanting in the young and has various degrees of development in the different species, in some of which it is wholly wanting. The species of _Acanthurus_ reach a large size, and in some the caudal spines are bright scarlet, in others blue. _Acanthurus unicornis_, the unicorn-fish, is the commonest species and the one with the longest horn. It is abundant in Japan, in Hawaii, and in the East Indies.

_Axinurus thynnoides_ of the East Indies has a long, slim body, with slender tail like a mackerel.

=Suborder Amphacanthi, the Siganidæ.=—The _Amphacanthi_ (ἄμφϊ, everywhere; ἄκανθα, spine) are spiny-rayed fishes certainly related to the _Teuthididæ_, but differing from all other fishes in having the last ray of the ventrals spinous as well as the first, the formula being I. 4, I. The anal fin has also six or seven spines; and the maxillary is soldered to the premaxillary. The skeleton is essentially like that of the _Acanthuridæ_.

The single family, _Siganidæ_, contains fishes of moderate size, valued as food, and abounding about rocks in shallow water from the Red Sea to Tahiti. The coloration is rather plain olive or brown, sometimes with white spots, sometimes with bluish lines. The species are very much alike and all belong to the single genus _Siganus_. One species, _Siganus fuscescens_, dusky with small, pale dots, is a common food-fish of Japan. Others, as _Siganus oramin_ and _Siganus vermiculatus_, occur in India, and _Siganus punctatus_, known as lo, abounds about the coral reefs of Samoa. _Siganus vulpinus_ differs from the others in the elongate snout.

A fossil genus, _Archoteuthis_ (_glaronensis_), is found in the Tertiary of Glarus. It differs from _Siganus_ in the deeper body and in the presence of six instead of seven spines in the anal fin.

The real relationship of the _Siganidæ_ is still uncertain, but the family is probably most nearly allied to the _Acanthuridæ_, with which the species were first combined by Linnæus, who included both in his genus _Teuthis_. In the structure of the vertical fins the _Siganidæ_ resemble the extinct genus _Pygæus_.