1911 Encyclopædia Britannica/Sea-horse

SEA-HORSE. Sea-horses (Hippocampina) are small marine fishes which, with pipe-fishes (Syngnathina), form the Lophobranchiate division of the suborder Thoracostei. The gills of the members 'of this group are not arranged in leaf-like series as in other fishes, but form a convex mass composed of small rounded lobes attached to the bronchial arches, as shown in the accompanying figure (fig. 1) of the head of a sea-horse, in which the gill-cover has been pushed aside to show the interior of the gill-cavity.

Fig. 1.—Gills of Hippocampus abdominalis.

Sea-horses differ from pipe-fishes by having a prehensile and invariably finless tail; it is long, slender, tapering, quadrangular in a transverse section, and, like the rest of the body, encased in a dermal skeleton, which consists of horny segments, allowing of ventral, and in a less degree of lateral, but not of dorsal, flexion. The typical sea-horse (Hippocampus) can coil up a great portion of its tail, and firmly attach itself by it to the stems of sea-weeds or similar objects. The body is compressed and more or less elevated, and the head terminates-~ in a long tubiform snout, at the end of which is the small mouth. The configuration of the fore part of the body, as well as the peculiar manner in which the head is joined to the neck-like part of the trunk, bears a striking resemblance to a horse’s head. Seahorses are bad swimmers and are unable to resist currents. With the aid of their single dorsal fin, which is placed about the middle of the fish’s body and can be put into a rapid undulatory motion, they shift from time to time to some object near them, remaining stationary among vegetation or coral where they find the requisite amount of food and sufficient cover. Their coloration and the tubercles or spines on the head and body, sometimes with the addition of skinny flaps and filaments, closely resemble their surroundings, and constitute the means by which these defenceless creatures escape detection by their enemies. These protective structures are most developed in the Australian genus Phyllopteryx, one of the most singular types of littoral fishes.

Sea-horses belong to the tropics and do not extend so far north as pipe-fishes. They are abundant at suitable localities, chiefly on the coral-banks of the Indo-Pacific Ocean. Some forty species are known, of which the majority belong to the genus Hippocampus proper.

Fig. 2.—Phyllopteryx eques.

They vary from 2 to 12 in. in length; but in China and Australia a genus (Solenognathus) occurs, the species of which attain to a length of nearly 2 ft.; they, however, in form resemble pipe-fishes rather than sea-horses. The species which may be sometimes seen in European aquaria is Hippocampus antiquorum, common in the Mediterranean and on the coasts of Portugal and France. It is rare on the south coast of England, but it has often been captured on the Essex coast. About 1885, according to Dr J. Murie, two Leigh fishermen when shrimping at Harwich during the summer season succeeded in procuring altogether between 100 and 120 specimens. The food of the sea-horses consists probably of very small invertebrates and the fry of other fishes. Like the other Lophobranchiates, they take great care of their, progeny. The male Hippocampus carries the ova in a sac on the lower side of the tail, in which they are hatched; in the other genera no closed pouch is developed, and the ova are embedded in the soft and thickened integument of either the abdomen or the tail.

All that is known of the habits of these interesting fishes will be found summarized in a valuable paper by T. Gill, “The Life History of the Sea-Horses (Hippocampids),” in Proc. U.S. Nat. Mus. xxviii. (1905), p. 805.