Fig. 187.—Æoliscus heinrichi Heckel. Eocene of Carpathia. Family Centriscidæ. (After Heckel.)
A fossil species, Æoliscus heinrichi, is found in the Oligocene of various parts of Europe, and Centriscus longirostris occurs in the Eocene of Monte Bolca.
In the Centriscidæ and Macrorhamphosidæ the expansions of the hypocoracoid called infraclavicles are not developed.
The Lophobranchs.—The suborder Lophobranchii (λοφός, tuft; βραγχός, gill) is certainly an offshoot from the Hemibranchii and belongs likewise among the forms transitional from soft to spiny-rayed fishes. At the same time it is a degenerate group, and in its modifications it turns directly away from the general line of specialization.
The chief characters are found in the reduction of the gills to small lobate tufts attached to rudimentary gill-arches. The so-called infraclavicles are present, as in most of the Hemibranchii. Bony plates united to form rings take the place of scales. The long tubular snout bears the short toothless jaws at the end. The preopercle is absent, and the ventrals are seven-rayed or wanting. The species known as pipefishes and sea-horses are all very small and none have any economic value. They are numerous in all warm seas, mostly living in shallow bays among seaweed and eel-grass. The muscular system is little developed and all the species have the curious habit of carrying the eggs until hatched in a pouch of skin under the belly or tail; this structure is usually found in the male.
The Solenostomidæ.—The Solenostomidæ of the East Indies are the most primitive of these fishes. They have the body rather short and provided with spinous dorsal, and ventral fins. The pretty species are occasionally swept northward to Japan in the Black Current. Solenostomus cyanopterus is a characteristic species. Solenorhynchus elegans, now extinct (with the trunk more elongate), preceded Solenostomus in the Eocene of Monte Bolca.
The Pipefishes: Syngnathidæ.—The Syngnathidæ are very long and slender fishes, with neither spinous dorsal, nor ventral fins, the body covered by bony rings. Of the pipefish, Syngnathus, there are very many species on all northern coasts. Syngnathus acus is common in Europe, Syngnathus fuscum along the New England coast, Syngnathus californiense in California, and Syngnathus schlegeli in Japan. Numerous other species of Syngnathus and other genera are found further south in the same regions. Corythroichthys is characteristic of coral reefs and Microphis of the streams of the islands of Polynesia. In general, the more northerly species have the greater number of vertebræ and of bony rings. Tiphle tiphle is a large pipefish of the Mediterranean. This species was preceded by Tiphle albyi (Siphonostoma) in the Miocene of Sicily. Other pipefishes, referred to as Syngnathus and Calamostoma, are found as fossils in Tertiary rocks.
The Sea-horses: Hippocampus.—Both fossil and recent forms constitute a direct line of connection from the pipefishes to the sea-horses. In the latter the head has the form of the head of a horse. It is bent at right angles to the body like the head of a knight at chess. There is no caudal fin, and the tail in typical species is coiled and can hardly be straightened out. Calamostoma of the Eocene, Gasterotokeus of Polynesia, and Acentronura of Japan are forms which connect the true sea-horses with the pipefish. Gasterotokeus has the long head and slender body of the pipefish, with the prehensile finless tail of a sea-horse. Most of the living species of the sea-horse belong to the genus Hippocampus. These little creatures have the egg-sac of the male under the abdomen. They range from two inches to a foot in length and some of the many species may be found in abundance in every warm sea. Some cling by the tails to floating seaweed and are swept to great distances; others cling to eel-grass and live very near the shore. The commonest European species is Hippocampus hippocampus. Most abundant on our Atlantic coast is Hippocampus hudsonius. Hippocampus coronatus is most common in Japan. The largest species are Hippocampus ingens of Lower California and Hippocampus kelloggi in Japan. Many species, especially of the smaller ones, have the spines of the bony plates of the body ending in fleshy flaps. These are sometimes so enlarged as to simulate leaves of seaweed, thus serving for the efficient protection of the species. These flaps are developed to an extreme degree in Phyllopteryx eques, a pipefish of the East Indies.
Fig. 188.—Solenostomus cyanopterus Bleeker. Misaki, Japan.