the Week of Proper 26 / Ordinary 31
Click here to learn more!
Bible Encyclopedias
Starfish
1911 Encyclopedia Britannica
or a popular term under which are included a large number of sea-animals, belonging all to the great group of Echino derms, but to three dis tinct divisions of that group: the Asterids, the Ophiurids and the Crinoids (see Echino Derma). The Asterids or starfish proper in clude the cross-fish, the b sun-star (see Echinoderma, fig. 17), the cushion-star, the butthorn, and many without a popular name. The common cross-fish or five-finger, Asterias rubens, of British seas, FIG. - An Asterid, Asterias rubens, may be taken as typical upper surface. (figs. i and 2), and the a, Madreporite.
a, The same magnified. description will apply b, Anus. also to the American This starfish may be 9-12 in. across. species A. forbesi and A. vulgaris. The animal consists of a central body or disk, produced into five arms or rays. The upper surface is covered with a leathery skin, strengthened by a rafter-work of little bones or plates, made of crystalline carbonate of lime, many of them bearing prickles of the same substance and small pincer-like bodies - the pedicellariae (see SEA-Urchin). In the middle of the body is a small anal opening, and near the angle between two rays is a furrowed plate pierced by many minute pores and called the madreporite. The under surface of the body has the mouth in the centre, and from it deep grooves radiate to the ends of the arms. At the bottom of each groove is a water-vessel, which gives off branches to the podia or suckingfeet on each side of it. A section across this groove is given in the article Echinoderma, fig. 1 2 B. The arrange and working of this FIG. 2. - Asterias rubens, under surface. ment hydraulic system is a, The arm-groove with its row of suckingfeet or podia.
essentially the same as b, End of a podium, magnified. in the sea-urchin, except for the presence of plates at the bottom of the groove beneath th.e radial water-vessel, and the absence of any plates covering the groove. At the end of each ray is, as in the urchin, a single tentacle surrounded by pigment and connected with a definite plate called "terminal." Thus the terminals of a starfish correspond to the oculars of a sea-urchin (see Echinoderma, fig. 3). The stomach is not a long coil, but a simple sac with branched blind tubes extending into each ray. A generative gland also passes down the side of each ray, and emits the milt or eggs when ripe through a pore near the body. Spawning takes place in spring or early summer. A starfish can crawl in any direction by means of its sucking-feet, whether the surface be hard or rough or polished, or the softest silt, whilst its supple body can squeeze through incredibly narrow crevices. The rate of progress is about six inches a minute.
The starfish are the scavengers of the sea, but unfortunately do. not confine their attentions to decaying matter; they eat oysters, clams, mussels, barnacles, sea-snails, worms, crustacea and even smaller starfish. There is constant war between oyster-fishers and starfish; no less than 42,000 bushels of starfish were removed from the oyster-beds of Connecticut in a single year, but not till they had worked damage to the amount of $631,500. The simplest way in which a starfish eats is by taking small bits of food into the stomach, and ejecting the refuse again through the mouth. But since the mouth is quite small and the food often large, the starfish finds it more convenient to turn its stomach inside out and to wrap it around the animal to be eaten, which is then digested quietly and the stomach withdrawn again. In the case of oysters and similar bivalves, the starfish first has to open them; and this it does by fixing the suckers of one or two rays to one valve and those of the opposite rays to the other valve, while it may get a purchase by also holding on to some neighbouring object. It then begins to straighten out its rays. The oyster can withstand a very strong pull, but it cannot hold out against a long pull, and the starfish does not hurry. At last the oyster gives way, and the starfish has its reward; but its companions often join in, and you may see a whole ball of them interlaced round half-digested molluscs and rolling about. Starfish begin to eat voraciously when quite young; one less than 5th in. across has been observed to eat over fifty young clams of half that length in six days. The more a starfish has to eat the quicker it grows, and it may become sexually mature in less than a year, then producing many thousands of young. Fortunately the increase is kept in check by many causes. The young, while still in the stage of free-swimming larvae, are swallowed in millions by various fish. When they settle down on seaweed their bright colours attract eels and many small fishes. Later in life they are attacked by parasites, while those which stray into shallow water are eaten by gulls and crows. Freshets and cold currents are also destructive.
