Fig. 422.—Eutæniichthys gillii Jordan & Snyder. Tokyo, Japan.
Its eyes are represented by mere rudiments, their loss being evidently associated with the peculiar habit of the species, which clings to the under side of stones in relative darkness, though in very shallow water. The flesh is also colorless, the animal appearing pink in life.
In the Japanese species Luciogobus guttatus, common under stones and along the coast, the spinous dorsal, weak in numerous other species, finally vanishes altogether. Other gobies are band-shaped or eel-shaped, the dorsal spines being continuous with the soft rays. Among these are the barreto of Cuba, Gobioides broussoneti, and in Japan Tænioides lacepedei and Trypauchen wakæ, the latter species remarkable for its strong canines. Fossil gobies are practically unknown. A few fragments, otoliths, and partial skeletons in southern Europe have been referred to Gobius, but no other genus is represented.
The family of Oxudercidæ contains one species, Oxuderces dentatus, a small goby-like fish from China. It is an elongate fish, without ventral fins, and with very short dorsal and anal.
Suborder Discocephali, the Shark-suckers: Echeneididæ.—Next to the gobies, for want of a better place, we may mention the singular group of Discocephali (δίσκος, disk; κεφαλή, head). In this group the first dorsal fin is transformed into a peculiar laminated sucking-disk, which covers the whole top of the head and the nape. In other respects the structure does not diverge very widely from the percoid type, there being a remarkable resemblance in external characters to the Scombroid genus Rachycentron. But the skeleton shows no special affinity to Rachycentron or to any perciform fish. The basis of the cranium is simple, and in the depression of the head with associated modifications the Discocephali approach the gobies and blennies rather than the mackerel-like forms.
Fig. 423.—Sucking-fish, or Pegador, Leptecheneis naucrates (Linnæus). Virginia.
The Discocephali comprise the single family of shark-suckers or remoras, the Echeneididæ. All the species of this group are pelagic fishes, widely diffused in the warm seas. All cling by their cephalic disks to sharks, barracudas, and other free-swimming fishes, and are carried about the seas by these. They do not harm the shark except by slightly impeding its movement. They are carnivorous fishes, feeding on sardines, young herring, and the like. When a shark, taken on the hook, is drawn out of the water the sucking-fish leaves it instantly, and is capable of much speed in swimming on its own account. These fishes are all dusky in color, the belly as dark as the back, so as to form little contrast to the color of the shark.
The commonest species, Leptecheneis naucrates, called pegapega or pegador in Cuba, reaches a length of about two feet and is almost cosmopolitan in its range, being found exclusively on the larger sharks, notably on Carcharias lamia. It has 20 to 22 plates in its disk, and the sides are marked by a dusky lateral band.