The Lancet-fishes.—The Plagyodontidæ (Alepisauridæ) contains the lancet-fishes, large, swift, scaleless fishes of the ocean depths with very high dorsal fin, and the mouth filled with knife-like teeth. These large fish are occasionally cast up by storms or are driven to the shores by the torments of a parasite, Tetrarhynchus, found imbedded in the flesh.
It is probable that they are sometimes killed by being forced above their level by fishes which they have swallowed. In such cases they are destroyed through the reduction of pressure.
Every part of the body is so fragile that perfect specimens are rare. The dorsal fin is readily torn, the bones are very feebly ossified, and the ligaments connecting the vertebræ are very loose and extensible, so that the body can be considerably stretched. "This loose connection of the parts of the body is found in numerous deep-sea fishes, and is merely the consequence of their withdrawal from the pressure of the water to which they are exposed in the depths inhabited by them. When within the limits of their natural haunts, the osseous, muscular, and fibrous parts of the body will have that solidity which is required for the rapid and powerful movements of a predatory fish. That the fishes of this genus (Plagyodus) belong to the most ferocious of the class is proved by their dentition and the contents of their stomach." (Günther.) Dr. Günther elsewhere observes: "From the stomach of one example have been taken several octopods, crustaceans, ascidians, a young Brama, twelve young boarfishes (Capros), a horse-mackerel, and one young of its own species."
Fig. 96.—Lancet-fish, Plagyodus ferox (Lowe). New York.
The lancet-fish, Plagyodus ferox, is occasionally taken on either side of the Atlantic and in Japan. The handsaw-fish, called Plagyodus æsculapius, has been taken at Unalaska, off San Luis Obispo, and in Humboldt Bay. It does not seem to differ at all from Plagyodus ferox. The original type from Unalaska had in its stomach twenty-one lumpfishes (Eumicrotremus spinosus). This is the species described from Steller's manuscripts by Pallas under the name of Plagyodus. Another species, Plagyodus borcalis, is occasionally taken in the North Pacific.
The Evermannellidæ is a small family of small deep-sea fishes with large teeth, distensible muscles, and an extraordinary power of swallowing other fishes, scarcely surpassed by Chiasmodon or Saccopharynx. Evermannella (Odontostomus, the latter name preoccupied) and Omosudis are the principal genera.
The Paralepidæ are reduced allies of Plagyodus, slender, silvery, with small fins and fang-like jaws. As in Plagyodus, the adipose fin is developed and there are small luminous dots. The species are few and mostly northern; one of them, Sudis ringens, is known only from a single specimen taken by the present writer from the stomach of a hake (Merluccius productus), the hake in turn swallowed whole by an albacore in the Santa Barbara Channel. The Sudis had been devoured by the hake, the hake by the albacore, and the albacore taken on the hook before the feeble Sudis had been digested.
Fig. 97.—Eurypholis sulcidens Pictet, restored. Family Enchodontidæ. Upper Cretaceous of Mt. Lebanon. (After Woodward, as E. boissieri.)