CHAPTER XXIV

SERIES PLECTOGNATHI

=THE Plectognaths.=—Derived directly from the _Acanthuridæ_, from which they differ by progressive steps of degeneration, are the three suborders of _Sclerodermi_, _Ostracodermi_, and _Gymnodontes_, forming together the series or suborder of _Plectognathi_. As the members of this group differ from one another more widely than the highest or most generalized forms differ from the _Acanthuridæ_, we do not regard it as a distinct order. The forms included in it differ from the _Acanthuridæ_ much as the swordfishes differ from ordinary mackerel. The _Plectognathi_ (πλεϡτός, woven together; γνάθος, jaw) agree in the union of the maxillary and premaxillary, in the union of the post-temporal with the skull, in the great reduction of the gill-opening, and in the elongation of the pelvic bones. All these characters in less degree are shown in the _Squamipinnes_. We have also the reduction and final entire loss of ventral fins, the reduction and loss of the spinous dorsal, the compression and final partial or total fusion of the teeth of the upper jaw, the specialization of the scales, which change from bony scutes into a solid coat of mail on the one hand, and on the other are reduced to thorns or prickles and are finally altogether lost. The number of vertebræ is also progressively reduced until in the extreme forms the caudal fin seems attached to the head, the body being apparently wanting. Throughout the group poisonous alkaloids are developed in the flesh. These may produce the violent disease known as ciguatera, directly attacking the nervous system. See p. 182, vol. I.

The three suborders of plectognathous are easily recognized by external characters. In the _Sclerodermi_ (σκλερός, hard; δέρμα, skin) the spinous dorsal is present and the body is more or less distinctly scaly. The teeth are separate and incisor-like and the form is compressed. In the _Ostracodermi_ (ὀστράκος, a box; δέρμα, skin) there is no spinous dorsal, the teeth are slender, and the body is inclosed in an immovable, bony box. In the _Gymnodontes_ (γυμνός, naked; ὀδούς, tooth) the teeth are fused into a beak like that of a turtle, either continuous or divided by a median suture in each jaw, the spinous dorsal is lost, and the body is covered with thorns or prickles or else is naked.

=The Scleroderms.=—The _Sclerodermi_ include three recent and one extinct families. Of the recent forms, _Triacanthidæ_ is the most primitive, having the ventral fins each represented by a stout spine and the skin covered with small, rough scales. The dorsal has from four to six stiff spines.

_Triacanthodes anomalus_ is found in Japan, _Hollardia hollardi_ in Cuba. _Triacanthus brevirostris_, with the first spine very large, is the common hornfish of the East Indies ranging northward to Japan.

=The Trigger-fishes: Balistidæ.=—The _Balistidæ_, or trigger-fishes, have the body covered with large rough scales regularly arranged. The first dorsal fin is composed of a short stout rough spine, with a smaller one behind it and usually a third so placed that by touching it the first spine may be set or released. This peculiarity gives the name of trigger-fish as well as the older name of _Balistes_, or cross-bow shooter. There are no ventral fins, the long pelvis ending in a single blunt spine. The numerous species of trigger-fishes are large coarse fishes of the tropical seas occasionally ranging northward. The center of distribution is in the East Indies, where many of the species are most fantastically marked. _Balistes carolinensis_, the leather-jacket, or cucuyo, is found in the Mediterranean as also on the American coast. _Balistes vetula_, the oldwife, oldwench, or cochino, marked with blue, is common in the West Indies, as are several other species, as _Canthidermis sufflamen_, the sobaco, and the jet-black _Melichthys piceus_, the black oldwife, or galafata. Several species occur on the Pacific Coast of Mexico, the Pez Puerco, _Balistes verres_, being commonest. Still others are abundant about the Hawaiian Islands and Japan. The genus _Balistapus_, having spinous plates on the tail, contains the largest number of species, these being at the same time the smallest in size and the most oddly colored. _Balistapus aculeatus_ and _Balistapus undulatus_ are common through Polynesia to Japan. Most of the tropical species of _Balistidæ_ are more or less poisonous, causing ciguatera, the offensive alkaloids becoming weaker in the northern species. _Melichthys radula_ abounds in Polynesia. In this species great changes take place at death, the colors changing from blue and mottled golden green to jet black. Other abundant Polynesian species are _Xanthichthys lineopunctatus_, _Balistes vidua_, _Balistes bursa_, and _Balistes flavomarginatus_.

=The File-fishes: Monacanthidæ.=—Closely related to the _Balistidæ_ are the _Monacanthidæ_, known as filefishes, or foolfishes. In these the body is very lean and meager, the scales being reduced to shagreen-like prickles. The ventral fins are replaced by a single movable or immovable spine, which is often absent, and the first dorsal fin is reduced to a single spine with sometimes a rudiment behind it. The species are in general smaller than the _Balistidæ_ and usually but not always dull in color. They have no economic value and are rarely used as food, the dry flesh being bitter and offensive. The species are numerous in tropical and temperate seas, although none are found in Europe. On our Atlantic coast, _Stephanolepis hispidus_ and _Ceratacanthus schœpfi_ are common species. In the West Indies are numerous others, _Osbeckia lævis_ and _Alutera güntheriana_, largest in size, among the commonest. Both of these are large fishes without ventral spine. _Monacanthus chinensis_, with a great, drooping dewlap of skin behind the ventral spine, is found on the coast of China. Of the numerous Japanese species, the most abundant and largest is _Pseudomonacanthus modestus_, with deep-blue fins and the ventral spine immovable. Another is _Stephanolepis cirrhifer_, known as _Kawamuki_, or skin-peeler. _Alutera monoceros_, and _Osbeckia scripta_, the unicorn fish, abound in the East Indies, with numerous others of less size and note. In the male of the Polynesian _Amanses scopas_ (Fig. 347) the tail is armed with a brush of extraordinarily long needle-like spines.

In _Stephanolepis spilosomus_ the caudal fin is of a brilliant scarlet color, contrasting with the usual dull colors of these fishes. In _Oxymonacanthus longirostris_ the body is blue with orange checker-like spots and the snout is produced in a long tube. About the islands of Polynesia, filefishes are relatively few, but some of them are very curious in form or color.

=The Spinacanthidæ.=—In the extinct family _Spinacanthidæ_ the body is elongate, high in front and tapering behind. The first dorsal has six or seven spines, and there are rough spines in the pectoral. The teeth are bluntly conical. _Spinacanthus blennioides_ and _S. imperalis_ are found in the Eocene of Monte Bolca. These are probably the nearest to the original ancestor among known scleroderms.

=The Trunkfishes: Ostraciidæ.=—The group _Ostracodermi_ contains the single family of _Ostraciidæ_, the trunkfishes or cuckolds. In this group, the body is enveloped in a bony box, made of six-sided scutes connected by sutures, leaving only the jaws, fins and tail free. The spinous dorsal fin is wholly wanting. There are no ventral fins, and the outer fins are short and small. The trunkfishes live in shallow water in the tropical seas. They are slow of motion, though often brightly colored.

Against most of their enemies they are protected by the bony case. The species range from four inches to a foot in length, so far as known. They are not poisonous, and are often baked in the shell. Three genera are recognized: _Lactophrys_ with the _carapace_, three-angled; _Ostracion_ with four angles; and _Aracana_, resembling _Ostracion_, but with the carapace not closed behind the anal fin. In each of these genera there is considerable minor variation due to the presence or absence of spines on the bony shell. In some species, called cuckolds, or cowfishes, long horns are developed over the eye. Others have spines on some other part of the shield and some have no spines at all. No species are found in Europe, and none on the Pacific coast of America. The three-angled species, called _Lactophrys_, are native chiefly to the West Indies, sometimes carried by currents to Guinea, and one is described from Australia. _Lactophrys tricornis_ of the West Indies has long horns over the eye; _Lactophrys trigonus_ has spines on the lower parts only. _Lactophrys triqueter_ is without spines, and the fourth American species, _Lactophrys bicaudalis_, is marked by large black spots. The species of _Ostracion_ radiate from the East Indies. One of them, _Ostracion gibbosum_, has a turret-like spine on the middle of the back, causing the carapace to appear five-angled; _Ostracion diaphanum_ has short horns over the eye, and _Ostracion cornutum_ very long ones; _Ostracion_ _immaculatus_, the common species of Japan, is without spines; _Ostracion sebæ_ of Hawaii and Samoa is deep, rich blue with spots of golden. _Aracana_ is also of East Indian origin; _Aracana aculeata_, with numerous species, is common in Japan. A fossil species of _Ostracion_ (_O. micrurum_) is known from the Eocene of Monte Bolca.

=The Gymnodontes.=—The group of _Gymnodontes_, having the teeth united in a turtle-like beak, carry still further the degeneration of scales and fins. There is no trace of spinous dorsal, or ventral. The scales are reduced to thorns or prickles, or are lost altogether. All the species have the habit of inflating themselves with air when disturbed, thus floating, belly upward, on the surface of the water. Very few, and these only northern species, are used as food, the flesh of the tropical forms being generally poisonous, and that often in a higher degree than any other fishes whatever.

=The Triodontidæ.=—The most generalized family is that of the _Triodontidæ_. These fishes approach the _Balistidæ_ in several regards, having the body compressed and covered with rough scales. The teeth form a single plate in the lower jaw, but are divided on the median line above. The compressed, fan-like, ventral flap is greatly distensible. _Triodon bursarius_, of the East Indies and northward to Japan, is the sole species of the family.

=The Globefishes: Tetraodontidæ.=—In the _Tetraodontidæ_ (globefishes, or puffers), each jaw is divided by a median suture. The dorsal and anal are short, and the ventrals are reduced in number, usually fifteen to twenty (7 + 13 to 7 + 9). The walls of the belly are capable of extraordinary distension, so that when inflated, the fish appears like a globe with a beak and a short tail attached. The principal genus _Spheroides_ contains a great variety of forms, forming a closely intergrading series. In some of these the body is smooth, in others more or less covered with prickles, usually three-rooted. In some the form is elongate, the color silvery, and the side of the belly with a conspicuous fold of skin. In these species, the caudal is lunate and the other fins falcate, and with numerous rays. But these forms (called _Lagocephalus_) pass by degrees into the short-bodied forms with small rounded fins, and no clear line has yet been drawn separating the group into genera. In these species each nostril has a double opening. _Lagocephalus lagocephalus_, large and silvery, is found in Europe. _Lagocephalus lævigatus_ replaces it on the Atlantic Coast of North America. In Japan are numerous forms of this type, the venomous _Lagocephalus sceleratus_ being one of the best known. Numerous other Japanese species, _Spheroides xanthopterus_, _rubripes_, _pardalis_, _ocellatus_, _vermiculatus_, _chrysops_, etc., mark the transition to typical _Spheroides_. _Spheroides maculatus_ is common on our Atlantic coast, the puffer, or swell-toad of the coastwise boys who tease it to cause it to swell. _Spheroides spengleri_ and _S. testudineus_ abound in the West Indies. _Spheroides politus_ on the west coast of Mexico.

In _Tetraodon_ the nasal tentacle is without distinct opening, its tip being merely spongy. The species of this genus are even more inflatable and are often strikingly colored, the young sometimes having the belly marked by concentric stripes of black which disappear with age. _Tetraodon hispidus_ abounds in estuaries and shallow bays from Hawaii to India. In Hawaii, it is regarded as the most poisonous of all fishes (muki-muki) and it is said that its gall was once used to poison arrows. _Tetraodon fahaka_ is a related species, the first known of the family. It is found in the Nile. _Tetraodon lacrymatus_, black with white spots, is common in Polynesia. _Tetraodon aërostaticus_, with black spots, is frequently taken in Japan, and _Tetraodon setosus_ is frequent on the west coast of Mexico. This species is subject to peculiar changes of color. Normally dark brown, with paler spots, it is sometimes deep blue, sometimes lemon-yellow and sometimes of mixed shades. Specimens showing these traits were obtained about Clarion Island of the Revillagigedos. No _Tetraodon_ occurs in the West Indies. _Colomesus psittacus_, a river fish of the northern part of South America, resembles _Spheroides_, but shows considerable difference in the skull.

But few fossil _Tetraodontidæ_ have been recognized. These are referred to _Tetraodon_. The earliest is _Tetraodon pygmæus_ from Monte Bolca.

The _Chonerhinidæ_ of the East Indies are globefishes having the dorsal and anal fins very long, the vertebræ more numerous (12 + 17), twenty-nine in number. _Chonerhinus naritus_ inhabits the rivers of Sumatra and Java.

The little family of _Tropidichthyidæ_ is composed of small globefishes, with a sharply-keeled back, and the nostrils almost, or quite, wanting. The teeth are as in the _Tetraodontidæ_. The skeleton differs considerably from that of _Spheroides_, apparently justifying their separation as a family. The species are all very small, three to six inches in length, and prettily colored. In the West Indies _Tropidichthys rostratus_ is found. _Tropidichthys solandri_ abounds in the South Seas, dull orange with blue spots. _Tropidichthys rivulatus_ is common in Japan and several ether species are found in Hawaii.

Other species occur on the west coast of Mexico, in Polynesia, and in the East Indies.

=The Porcupine-fishes: Diodontidæ.=—In the remaining families of _Gymnodontes_, there is no suture in either jaw, the teeth forming an undivided beak. The _Diodontidæ_, or porcupine-fishes, have the body spherical or squarish, and armed with sharp thorns, the bases of which are so broad as to form a continuous coat of mail. In some of them, part of the spines are movable, these being usually two-rooted; in others, all are immovable and three-rooted. All are reputed poisonous, especially in the equatorial seas.

In _Diodon_ the spines are very long, the anterior ones, at least, movable. The common porcupine-fish, _Diodon hystrix_, is found in all seas, and often in abundance. It is a sluggish fish, olive and spotted with black. It reaches a length of two feet or more, and by its long spines it is thoroughly protected from all enemies. A second species, equally common, is the lesser porcupine-fish, _Diodon holacanthus_. In this species, the frontal spines are longer than those behind the pectoral, instead of the reverse, as in _Diodon hystrix_. Many species of _Diodon_ are recorded from the Eocene, besides numerous species from later deposits. One of these, as _Heptadiodon heptadiodon_ from the Eocene of Italy, with the teeth subdivided, possibly represents a distinct family. _Diodon erinaceus_ is found in the Eocene of Monte Bolca and _Progymnodon hilgendorfi_ in the Eocene of Egypt.

In the rabbit-fishes (_Chilomycterus_) the body is box-shaped, covered with triangular spines, much shorter and broader at base than those of _Diodon_. Numerous species are known.

_Chilomycterus schœpfi_ is the common rabbit-fish, or swell-toad of our Atlantic coast, light green, prettily varied with black lines. The larger, _Chilomycterus affinis_, with the pectoral fin spotted with black, is widely diffused through the Pacific. It is rather common in Japan, where it is the torabuku, or tiger puffer. It is found also in Hawaii, and it is once recorded by Dr. Eigenmann from San Pedro, California, and once by Snodgrass and Heller, from the Galapagos.

=The Head-fishes: Molidæ.=—The headfishes, or _Molidæ_, also called sunfishes, have the body abbreviated behind so that the dorsal, anal, and caudal fins seem to be attached to the posterior outline of the head. This feature, constituting the so-called gephyrocercal tail is a trait of specialized degradation.

_Mola mola_, the common head-fish or sunfish, is found occasionally in all tropical and temperate seas. Its form is almost circular, having been compared by Linnæus to a mill-wheel (mola), and its surface is covered with a rough, leathery skin. It swims very lazily at the surface of the water, its high dorsal often rising above the surface. It is rarely used as food, though not known to be poisonous. The largest example known to the writer was taken at Redondo Beach, California, by Mr. Thomas Shooter, of Los Angeles. This specimen was 8 feet 2 inches in length, and weighed 1200 pounds. Another, almost as large, was taken at San Diego, in April, 1904. No difference has been noticed among specimens from California, Cape Cod, Japan, and the Mediterranean. The young, however, differ considerably from the adult, as might be expected in a fish of such great size and extraordinary form. (See Figs. 109 and 110, Vol. I.)

Fragments named _Chelonopsis_, and doubtfully referred to _Mola_, are found in the Pliocene of Belgium. Certain jaws of cretaceous age, attributed to _Mola_, probably belong, according to Woodward, to a turtle.

In the genus _Ranzania_, the body is more elongate, twice as long as deep, but as in _Mola_, the body appears as if bitten off and then provided with a fringe of tail. The species are rarely taken. _Ranzania truncata_ is found in the Mediterranean and once at Madeira. _Ranzania makua_, known as the king of the mackerels about Hawaii, is beautifully colored brown and silvery. This species has been taken once in Japan.

In Hawaii it is believed that all the Scombroid fishes are subject to the rule of the makua and that they will disappear if this fish be killed. By a similar superstition, _Regalecus glesne_ is "king of the herrings" in Norway and about Cape Flattery, _Trachypterus rex salmonorum_ is "king of the salmon."