Sea Cucumber, one of the popular names of the holothuria, the highest order of the echinoderms, which are the highest class of radiated animals; the name is derived from their generally elongated and more or less cylindrical and warty form; they are also called sea slugs from their vermicular mode of creeping. The body is rather soft, with a leathery skin sometimes furnished with calcareous plates or granules without spines; the mouth is at one end and the cloacal opening at the other, the former surrounded by branching and retractile tentacles supported on an osseous ring which forms the rudiment of an internal skeleton; the ambulacra (feet) or suckers are arranged usually in longitudinal rows on the sides of the body, alternating with spaces having no such apparatus, and corresponding to the spiny rows of star fishes and sea urchins; motion is effected principally by these suckers, the mouth forward. By the introduction or ejection of water at the posterior extremity the body may be made to assume great variations in length and width, and the general appearance externally is more that of an annelid than a radiate. Some of the genera (as synapta) have cutaneous anchor-like hooks by which they attach themselves, each inserted obliquely under a small subcutaneous scale perforated by a canal.
The muscular layer under the skin is very thick, and so powerful in its constrictions that the animal can discharge all its viscera through the mouth. They have a well developed oesophageal ring, which sends off nerves to the body and tentacles; the intestinal canal is very long, retained in place by a kind of membranous mesentery, and generally unsymmetrical; they have a distinct vascular system, but no heart; the tubes for the water for respiration are much branched, and open from the cloaca; respiration is also effected partly by the tentacles around the mouth, which communicate with the aquiferous system, and by the water introduced into the visceral cavity. The feet are either in five rows as on the ribs of a melon, or only on the lower surface, or on a kind of ventral disk; their motions at the bottom of the sea are aided also by the oral prehensile tentacles. The quinary system prevails among holothurians as among other echino-derms. The sexes are distinct; some multiply by fissuration, but most by means of eggs; in the first form the young has an oval ciliated body, like an infusorial animalcule, without external organs or distinction of parts; in the next larval change the organs are developed, at first in a bilateral manner (according to Mül-ler), and then pass into the radiated type by a process of internal gemmation, receiving new locomotive organs in the ciliated fringe as they pass into the pupa form, from which the true echinoderm is developed. - The old genus holo-thuria (Linn.) has been variously subdivided.
They are generally small on the New England coast, but attain a large size in the bay of Fundy and on the banks of Newfoundland; on the mud flats of the Florida reefs they are sometimes seen more than a foot long and 3 or 4 in. in circumference. All along the American coast is found the sclerodactyla Briareus (Ayres), from 3 to 6 in. long, dark brown, with 10 very branching tentacles; it lives on muddy bottoms in shallow water among the roots of żos-tera. The Cuvieria Fabricii (Dub. and Kor.; H. squamata, Fabr.) is about 3 in. long, and bright brick-red, the color being readily imparted to alcohol and even to water; it is scaled and granulated above, and has 10 tentacles; it is generally caught on hooks, and occurs on the coast of New England. The chiro-dota arenata (Gould) is 5 to 6 in. long, club-shaped, ending posteriorly in a tube about the size of a crow quill; the color is light drab, with calcareous granules; it is found on our beaches after storms, and lives in shallow water. The botryodactyla grandis (Ayres) is very abundant in the bay of Fundy and on the banks of Newfoundland, and attains a length of 6 to 8 in.; when boiled it is very palatable.
From researches made on the American coast it appears that the laminarian zone just below low-water mark is the favorite residence of holothurians, though a few occur in deep water. Those found in shallow water are the most common. The sea urchins live in deeper water, and the star fishes are the lowest both in habitat and in the radiated scale. The breeding season here seems to be the winter and spring. For a description of the 8 genera and 13 species of the American coast, all of which are different from those of Europe, see "Proceedings of the Boston Society of Natural History," vol. iv. (1851-'2), where Dr. W. O. Ayres has carefully compared them. - Among the European species are the H. (psolus) phan-tapus (Linn.), with an almost scaly envelope, and the feet of its central disk arranged in three series; the H. squamata (Fabr.), a small species, with the lower surface flat and soft with a great number of feet, and rough and scaly above; and the H. tremula (Gmel.), of the Mediterranean, blackish, bristled above, with numerous feet below, and 20 branched tentacles, which grows to a foot in length, and is one of the species eaten by the Italian fishermen.
Several species of holothurians are collected in the East Indies for food, under the name of biche de mar or tripang, the taking and preparation of which employ great numbers of the Malays and Polynesians; the best are found on reefs of mixed coral and sand in the Feejee group in one or two fathoms of water, and are obtained by diving. They are boiled in their own liquid, then dried on stages in large heated houses, and meet with a ready sale at high prices in the Chinese markets as ingredients for rich soups. For an account of the mode of preparation, see vol. iii. of the "Narrative of the United States Exploring Expedition," under Capt. Wilkes, pp. 218-222, with a plate. Dr. Karl Semper has described and figured in great detail the holothurians of the Philippine islands in his Reisen im Archipel der Philippinen (3 vols., Leipsic, 1867-72). See also Wallace's "Malay Archipelago" (1869).
Sea Cucumber (Holothuria lutea).