Art. IV.—On a curious Parasite (Anthosoma smithii, Leach) from the Porbeagle Shark (Lamna cornubica).
[Read before the Wellington Philosophical Society, 6th July, 1887.]
The genus Anthosoma was created by Leach for the reception of a most curious crustacean, specimens of which were found adhering to the gill-covers of the Porbeagle Shark. (Lamna cornubica), that had been thrown ashore at Exmouth, in Devonshire. The species was named after Mr. T. Smith, the discoverer, who sent it to the British Museum, and it has remained the sole representative of the genus and family.* I am not aware of any record of the occurrence of this creature in Australian waters. Some weeks ago, however, a fine Porbeagle Shark was captured by fishermen belonging to this port, and exhibited by them for some days; it was then procured for the Museum. During the operation of skinning, the taxidermist noticed and procured the specimens now exhibited.
Although differing in minor details from Leach's description and figure, I have little hesitation in referring it to his species, especially as it was obtained from the same host.
[Footnote] * The description and figure were first published by Leach in the “Encyclopædia Britannica” of 1816.
The head is of tolerable size, and distinct, consisting of a stout, rather narrow and strongly convex, horny buckler, of an ovoid shape. It is very narrow, thick, and obtuse in front, where it has a furrow running across its dorsal surface, and a deep notch on each side, which thus forms a beak, and almost divides it into a separate segment. It extends backward for some length, and becomes considerably broader, covering a portion of the thorax.
The segments of the thorax are very indistinct. On the dorsal aspect are two foliaceous elytraform appendages of an oval shape, and of a light horny and granulated texture. Beneath these the remaining portion of the thorax is seen, of a fleshy structure, and apparently without divisions.
The abdomen is very small, consisting of one short segment, which gives off two small caudal appendages in the form of short, flat, blunt filaments of the same texture as the elytraform appendages. Immediately beneath the notch, on each side of the blunt peak, we see a small flat body, and from near the base of each of these we find the origin of the antennæ. These organs are rather long and slender, and consist of six articulations, tapering from the base to the extremity. The most remarkable organs attached to the head, however, are the first pair of foot-jaws. These arise from between the base of the antennæ, are very long and strong, and project forward beyond the head. They consist of three stout joints of considerable length, and of cylindrical shape; the second joint, near its apex, having a tooth or spine, the last being terminated by a curved hook, which points upwards and backwards. The second, of three joints also, is of nearly equal length, but much more slender, and has the terminal joint ovate, compressed, and bifid. The third pair is short, very thick, stout, of two joints, and terminates in a strong claw-shaped extremity. The feet are three pairs, and are all foliaceous. The structure of these members is very simple, being merely foliaceous lamellæ, which lap over each other and surround the thorax as with a shield. They are of a light horny texture and somewhat granulated, like the dorsal elytraform appendages. The oviferous tubes are straight and very long. (Baird, “Brit. Ent.,” p. 298.)
The form of the feet and structure of the foot-jaws indicate that this animal is capable of little motion, and lives a strictly parasitic existence. It buries its beak in the flesh of its host, and thereby causes him much irritation, as evidenced by the inflamed appearance of the parts attacked.
Anthosoma smithii (Leach).
(“Encyc. Brit.,” i. 406. t. 20. f. 1–6.)
“Animal of an elongated oval form, about ten lines in length, and of a ferruginous white colour, bordering upon yellow. When alive it has a black spot upon the middle of the head, which disappears after death. The dorsal elytraform appendages and foliaceous feet are sprinkled over with semi-transparent spots.” (Baird.)
The New Zealand specimens differ in size, the length of the body being six lines, and the oviferous tubes one inch in length. When alive, the buckler and oviferous tubes were a rich brown. The dorsal appendages and foliaceous feet were white. The feet were much swollen, and, in some instances, presented an almost globose outline.