Syngnathus.—Body with the ridges more or less distinct, the dorsal ridge of the trunk not being continuous with that of the tail. Pectoral fins well developed; caudal present. Dorsal fin opposite or near to the vent. Humeral bones firmly united into the breast-ring. Egg-pouch as in Siphonostoma.
The distribution of this genus nearly coincides with that of the family, some fifty species being known. S. acus, the great Pipe-fish (see Fig. [75], p. 163), is one of the most common European fishes, extending across the Atlantic and southwards to the Cape of Good Hope; it attains a length of 18 inches. Another very common species, frequently met at sea, and spread over nearly all the tropical and sub-tropical seas, is S. pelagicus, agreeably marked with alternate brown and silvery cross-bars.
Doryichthys.—Body with the ridges well developed. Pectoral and caudal fins present. Dorsal fin long or of moderate length, opposite to the vent. Humeral bones firmly united. Males with the lower ridges of the abdomen dilated, the dilated parts forming a broad groove for the reception of the ova.
In these Pipe-fishes the ova are not received in a completely closed pouch, but glued on to the surface of the abdomen. Twenty species from tropical seas.
Nerophis.—Body smooth, rounded, with scarcely any of the ridges distinct. Pectoral fin none, caudal absent or rudimentary, the tail tapering into a point. Dorsal fin of moderate length, opposite to the vent. The ova are attached to the soft integument of the abdomen of the male, and are not covered by lateral folds of the skin.
Seven species from the European seas and the Atlantic. N. æquoreus (Ocean Pipe-fish), N. ophidion (Straight-nosed Pipe-fish), and N. lumbriciformis (Little Pipe-fish), are common on the British coasts.
Protocampus.—The whole dermal skeleton is covered with skin. A broad cutaneous fold runs along the back in front and behind the dorsal; a similar fold along the abdomen. Pectoral fin none; caudal very small.
The single species of this remarkable genus, P. hymenolomus, occurs in the Falkland Islands. It may be regarded as an embryonal form of Nerophis, the median skin-folds being evidently remains of the fringe which surrounds the body of the embryo.
The other genera belonging to this group are, Icthyocampus, Nannocampus, Urocampus, Leptoichthys, Coelonotus, and Stigmatophora.
Hippocampina.—The tail is prehensile, and invariably without caudal fin.—Sea-horses.