Division V.—Gobiiformes.
No bony stay for the praeoperculum. Basis cranii simple. Spinous dorsal, if present, formed of few, flexible rays. None of the epipleural bones attached to the centra of the vertebrae in the praecaudal region. Scapula and coracoid more or less reduced or even vestigial; pterygials large, 4 or 5 in number, forming together a thin plate which is in contact with or narrowly separated from the clavicle; one or two of the pterygials in contact with the coracoid. Ventral fins thoracic.
The Gobiidae, which alone constitute this division, are not very remote from the Perciformes, and may have evolved out of a type not very different from the Percidae.
Fam. 1. Gobiidae.—Suborbital arch ligamentous or absent. Gill-membranes more or less broadly attached to isthmus; 4 to 6 branchiostegal rays; gills 4, a slit behind the fourth; pseudobranchiae often present. All or most of the praecaudal vertebrae with transverse processes bearing the ribs, to which epipleurals are attached. Post-temporal forked, as in normal Perciformes. Ventral fins with 1 feeble spine and 4 or 5 branched rays, often united to form a sucking disk, a transverse fold of skin at their base completing the cup.
Head usually more or less depressed, body varying from short and stout to elongate and eel-shaped, but never with a very high number of vertebrae, these varying from 24 to 37 (10-14 + 13-24); scales cycloid or ctenoid, or absent; no lateral line; mouth moderate or large, dentition various; soft dorsal and anal fins nearly equally developed, varying from very short to very elongate; usually a large anal papilla.
Fig. 420.—Gobius ruthensparri. Nat. size. (From Holt and Byrne, Report Fisheries Ireland for 1901.)
A large family of some 600 species, the great majority marine, mostly carnivorous and of small size. The largest form (Eleotris marmorata, from the rivers of Siam, Borneo, and Sumatra) grows to nearly 3 feet, whilst the smallest (Mistichthys luzonensis, from the Philippines) measures only 12 to 14 millimetres, and is believed to be the smallest known Vertebrate. Gobiids occur in all the seas outside the Arctic and Antarctic circles, and they have representatives in the fresh waters of all parts of the world.
The genera are numerous but difficult of definition. The following are the principal: Eleotris, Oxymetopon, Vireosa, Rhyacichthys, Gobius, Crystallogobius, Aphia, Gobiosoma, Gobiodon, Benthophilus, Typhlogobius, Luciogobius, Sicydium, Lentipes, Periophthalmus, Boleophthalmus, Amblyopus, Trypauchen, Trypauchenichthys. Oxuderces, which has been made the type of a distinct family, appears to differ from Trypauchen only in the absence of ventral fins. Fossils referred to Gobius have been described from the Upper Eocene and Miocene of Europe, but there is no satisfactory evidence that they really belong to this family.
Gobius, of which several species are of common occurrence on our shores, have attracted special interest from their habits during the much prolonged breeding season. The male, usually more brilliantly coloured than the female, mounts guard over the eggs, which are either simply fixed by the female to the under surface of stones or weeds, or in a sort of nest built and kept in constant repair by him. This nest is usually made of a shell of Cardium, Patella, Haliotis, etc., or of the carapace of a crab, with the convexity turned upwards and covered with sand; the sand underneath is hollowed out, and a round opening at the side, coated by a mucus secreted by the skin of the male fish, gives access to the interior; the eggs, which are elongate and pyriform, are stuck to the inner surface of the shell forming the roof.[[730]] A curious British form is Aphia pellucida, two inches long which, from its transparent and almost colourless body, has long been erroneously supposed to be the fry of some larger fish. Among exotic forms, mention should be made of the Blind Goby (Typhlogobius californiensis), two inches long, uniform light pink, scaleless, with the eyes very small, reduced to mere vestiges, covered by skin, and functional only in the young, living like a slug under rocks between tide marks on the coast of California;[[731]] and to the Walking-Fish or Jumping-Fish (Periophthalmus), of which various species are found in great abundance on the mud-flats at the mouths of rivers in tropical Africa, Asia, and North-West Australia, skipping about by means of the muscular, scaly base of their pectoral fins, with the head raised and bearing a pair of strongly projecting versatile eyes close together.[[732]]