PIPE-FISHES ( Syngnathina ), small fishes, which with the Seahorses form a distinct family, Syngnathidae, of Lophobranchiate FIG. I. - Syngnathus acus, Male, with sub-caudal pouch. Thoracostei. The name is derived from the peculiar form of their snout, which is produced into a more or less long tube, ending in a narrow and small mouth which opens upwards and is toothless. The body and tail are long and thin, snake-like, encased in hard integuments which are divided into regularly arranged segments. This dermal skeleton shows several longitudinal ridges, so that a vertical section through the body represents an angular figure, not round or oval as in the majority of other fishes. A dorsal fin is always present, and is the principal (in some species, the only) organ of locomotion. The ventral fins are as constantly absent, and the other fins may or may not be developed. The gill-openings are extremely small and placed near the upper posterior angle of the gill-cover. Most of the pipefishes are marine, only a few being fluviatile. Pipe-fishes are abundant on such coasts of the tropical and temperate zones as offer by their vegetation shelter to these defenceless creatures. They are very bad swimmers, slowly moving through the water by means of the rapid undulatory movement of the dorsal fin. Their tail, even when provided with a caudal fin, is of no use in swimming, and not prehensile as in sea-horses. Specimens, therefore, are not rarely found at a great distance from land, having been resistlessly carried by currents into the open ocean; one species, Syngnathus pelagicus, has an extraordinarily wide range over the tropical seas, and is one FIG. 2. - Sub-caudal of the common fishes inhabiting the Syngnathus vegetation of the Sargasso Sea. The with to leave the theyoung colour of these fishes often changes with pouch. One side of the sea-weeds among which they may be the membrane of the found, passing from brown to green or s id even brick-red. In pipe-fishes the male to admit ter o pusfhior. ead view of its i i Pouch n (Nasate. is provided with a pouch - in some species size.) on the abdomen, in others on the lower side of the tail - in which the ova are lodged during their development. This marsupial pouch is formed by a fold of the skin developed from each side of the trunk or tail, the free margins of the fold being firmly united in the median line throughout the period during which the eggs are being hatched. When the young are hatched the folds separate, leaving a wide slit, by which the young gradually escape when quite able to take care of themselves. Nearly a hundred different species of pipe-fishes are known, of which Siphonostoma typhle, Syngnathus acus (the Great Pipe-fish up to 18 in. in length), Nerophis aequoreus (Ocean Pipe-fish), Nerophis ophidion (Straightnosed Pipe-fish), and Nerophis lumbriciformis (Little Pipe-fish) are British species. The last three are destitute of a caudal fin.
A review of the extensive literature on the breeding habits of the Syngnathidae is given by E. W. Gudger, "The Breeding habits and the Segmentation of the Egg of the Pipefish," Proc. U.S. Nat. Mus. (1905), xxix. 447.