Sea-Cucumbers.
(HOLOTHURIADÆ.)
XX.
There is a very singular group of animals, the _Holothuriadæ_, that
claims a passing notice, from their near relation in structural
formation to the Sea-Urchins, although externally they also exhibit
a certain resemblance to the _Annelides_. They are commonly termed
Sea-Cucumbers, from the fancied likeness which they bear, both in shape
and colour, to their namesakes of the vegetable kingdom.
A Holothuria is very unattractive in appearance when lying listless
upon the sea-beach, but if a small specimen be transferred to the
aquarium, it exhibits features of a very singular and interesting
character. When about to change its position, the head, hitherto
concealed, is protruded and expanded, until it assumes the form of a
beautiful flower.
The animal moves principally by aid of sucker-like feet, similar in
form to those of the Asteriadæ, or Sea-Urchins. In most species, the
body is divided longitudinally into five rows of suckers. In some,
however, these organs are scattered over the entire surface, while in
the small Sea-Cucumber (_Psolus phantapus_), they are arranged in three
rows upon a soft, oblong, flat disc, situated beneath the body of the
animal, like the foot of a gasteropod mollusc.
Of one genus--the Trepang--many species are eaten by the omnivorous
inhabitants of the Celestial Empire, by whom it is employed in the
preparation of 'nutritious soups, in common with an esculent sea-weed,
shark's fins, edible birds' nests, and other materials affording much
jelly.' The intestines, which are generally found to be filled with
coral, and solid masses of madreporic rock, are extracted, and the
animal then boiled in sea-water and dried in smoke.
Nothing can possibly be less enticing than the black and shrivelled
carcases of these defunct gasteropods, as they are seen spread out and
exposed for sale in the China markets. There are many varieties of
Trepang, some being held in higher esteem than others,--hence the great
difference which exists in the price of the article. The lowest quality
being ten dollars, and the highest fifty dollars, per pecul of 133 lbs.
The following are titles by which a few of the Holothuriæ are known in
China:--
Great Black-Stone Trepang;
Peach-blossom Trepang;
Great White-Stone Trepang;
The Bald Trepang;
The Scarlet Trepang;
Great Clear-Ball Trepang;
The Middle Ash-Bald Trepang, &c., &c.
The illustration on Plate 11 gives a good idea of the typical form
of the Holothuriadæ. It represents a species of the genus Cucumaria,
_C. communis_, or common Sea-Cucumber. Its length is from four to
eight inches; but, like all its kindred, it possesses the power of
considerably extending or contracting its body at will. The Tentacula
are ten in number, pinnate and plumose, stalked and rather large. The
body is five-sided, with numerous suckers on the angles, but more on
the sides, which are papilose. The colour is yellow, or brownish-white,
although specimens found on the Irish coast exhibit a purplish hue.
This, the most common species of its genus, is an inhabitant of
deep water, and is therefore most frequently taken with the dredge.
Occasionally, specimens may be found after violent storms stranded on
various parts of the shores of the United Kingdom.
The Sea-Cucumbers possess the singular power of disembowelling
themselves upon the slightest provocation, and also of throwing off
their Tentacula entire. There is one species, indeed, that exhibits
a still more wonderful phenomenon. At certain times members of this
species will divide their body into a number of parts, each of which
will in due course become a new and completely-formed animal. After
this the reader will be prepared to learn, that to build up a new
inside, or create a new set of branchiæ, is to a Holothuria a very
trifling and insignificant task.