Crawfish, a macrourous or long-tailed crustacean, of the order decapoda and genus asta-cus. This genus is fluviatile, while the lobster, belonging to the same family but to the genus homarus, is marine. The body is elongated and somewhat compressed, and the abdomen tol. v. - 30 large; it is covered by a corneous envelope or carapace, terminating anteriorly in a wide, short, flattened beak, which covers the base of the 'eye pedicles. There are two pairs of antennae: the first pair of moderate length, with two terminal filaments; the external, or second pair, being much longer, with a large lamellar appendage on the upper surface of its pedicle. The mouth apparatus consists of two mandibles, two pairs of jaws, and three pairs of jaw feet, moving horizontally. The legs are five pairs, the first the largest, and ending in a two-bladed nipper or claw, by which objects are seized in the pursuit of prey and in self-defence; the second and third pairs are also didactylous, but smaller, and the fourth and fifth are single-pointed. The fifth thoracic ring is simply articulated to the preceding ones.
The abdomen is of about the same width for its whole length, presenting on each side a series of laminae prolonged so as to encase more or less the base of the false or swimming feet; the last segment is very wide, forming, with the two laminae from the sixth ring on each side, a large caudal fin, nearly even when expanded, the external plate having a transverse joint at its posterior third, the middle plate being round at the end, with a tooth on each side posteriorly. The sternum forms no plastron, as in the crab; the pincers of the first pair of feet are not so large in proportion, and are without the angle seen in the lobster. The swimming feet are five pairs, long and narrow; in the females all end in wide leaflike plates, with ciliated edges; in the males the first pair are styliform. The gills are very numerous, disposed in tufts, and arranged in rows at the base of the walking feet, and within the carapace; they are separated by cartilaginous plates, whose motions serve to introduce and expel the water, which issues at an aperture on each side of the mouth. According to Milne-Edwards, the duodenum has a great number of internal villosities, no valve between it and the rectum, the latter smooth, and no caecal appendage, the opposite of which is the case in the lobster.
The eyes have compound facets, and are supported on movable pedicles arising from the first segment of the head, and may be in a measure withdrawn into cavities answering the purposes of orbits. The organs of generation are distinct in the two sexes; the number of eggs is very great, and they are carried for a time attached to the false feet, under the tail. Like other decapods, the crawfish changes its shell annually, coming out with a new and tender one, which becomes hard in a few days; at each moult the animal increases considerably in size, and the change appears to be continued through life; the shell, which is an epidermic covering, consists of chitine united to calcareous salts. This genus also has the power of reproducing claws and feet which have been lost by accident. Their food is almost exclusively animal, both living and dead matter being eagerly devoured; fish, mollusks, aquatic larvae, terrestrial insects, and sometimes their own species, form the principal sources of their subsistence. Their enemies are also many; mammals frequenting the water, aquatic birds, voracious fishes, and even insect larvae, destroy great numbers of them, especially in their young state.
They are considered luxuries on the table, and are used by fishermen as bait; they are caught in nets, and may be easily taken from holes and under stones. In some of the Russian rivers they attain a large size, and are caught for the calcareous masses in their stomachs, which have been used to correct stomachal acidity. (See Crab Stones.) They delight in clear and running streams, but are common in lakes and ponds; they conceal themselves by day, and feed by night. The color is generally a light yellowish brown. The European crawfish (A. fluviatilis, Fabr.) has the large claws studded with granulations, and the beak with a tooth on the side near its internal third. Among the American species are the A. affinis (Say) and A. Bartonii (Bosc), found in the southern and western rivers; in these the claws and the carapace are less granular. Other species are described in South America and Australia by Milne-Edwards. Crawfish swim rapidly by means of the tail, whose strokes propel them backward; they crawl well on the bottom, and are sometimes seen at a considerable distance from streams, using holes filled with water, and occasional pools, as places of retreat.
From their propensity to eat carrion, Audubon calls them "little aquatic vultures." They are fond of burrowing in the mud, and from this habit are often great pests, undermining levees and embankments. In the Mammoth cave of Kentucky some of the crawfish are blind; they have the eye pedicles, but no facets, only simple integuments covered with hairs; very probably, as in the case of the blind fish of the same cave (amblyopsis spelceus), internal rudiments of a visual organ will be found, especially as it is said that some of these Crustacea have well developed eyes, as also do the crickets which live in the cave.
Crawfish (Astacus fluviatilis).