One solitary species of the Crinoid Star-fishes has of late years been found to flourish in our own seas; it is, however, affixed to a stalk (pedunculated) only in the early periods of its existence.
When first discovered by Mr. Thompson in its infant state, the Pentacrinus Europæus was believed to be a distinct animal. It was taken attached to the stems of zoophytes of different orders, and measured about three-fourths of an inch in height. In form it resembled a minute comatula mounted on the stalk of a Pentacrinus. Subsequent research has proved that the little stranger was merely the young state of the feather star Comatula rosacea, and that although for a certain period attached to a slender waving stem, the Pentacrinus, when arrived at a certain stage of development, feels fully able to start life on its own accord, and hence takes opportunity to break off its early ties, and become a free animal, dependent upon its own exertions for subsistence.
It is no uncommon thing, as a late writer forcibly remarks, in the inferior classes of the animal kingdom, to find animals permanently attached from the period of their birth, and during all their existence. Familiar examples of this occur in the oyster, and various other bivalve shell-fish, as well as in numerous compound zoophytes. We likewise meet with races which are free and locomotive in their first stages, and afterwards become permanently fixed; but an animal growing for a period in the similitude of a flower on a stem, and then dropping from its pedicle, and becoming during the remainder of its life free and peripatetic, is not only new, but without any parellel in the whole range of the organized creation.
The Comatula, or as it is commonly called, the Rosy Feather-star, is allowed to be without exception the most lively of all the star-fishes. Its movements in swimming are said to resemble exactly the alternating strokes given by the medusa to the liquid element, and have the same effect, causing the animal to raise itself from the bottom, and to advance back foremost even more rapidly than the medusa. It has ten very slender rays with numbers of long beards on the sides. The body, which is of a deep rose colour, is small and surrounded with ten little filiform rays. The extremities of these organs are shaped like claws, by means of which the animal attaches itself to various kinds of sea-weed, and other submarine objects.
The adult Comatula generally measures about five inches across its fully expanded rays.
Before treating of what are termed the true Star-fishes, we require to dwell briefly upon an intermediate family named by Professor Forbes the Ophiuridæ, 'from the long serpent or worm-like arms, which are appended to their round, depressed, urchin like bodies.... They hold the same relation to the Crinoidea that the true Star-fishes hold to the Sea-Urchins. They are spinigrade animals, and have no true suckers by which to walk, their progression being effected (and with great facility) by means of five long flexible-jointed processes placed at regular distances around their body, and furnished with spines on the sides and membraneous tentacula. These processes are very different from the arms of the true Star-fishes, which are lobes of the animal's body, whereas the arms of the Ophiuridæ are super-added to the body, and there is no excavation in them for any longation of the digestive organs.'[16]
The British Ophiuridæ are now classed under two genera; of the Ophiuræ, or Sand-stars only two species (O. texturata and O. albida) are found on our shores; and the Ophicomæ, or Brittle-stars, of which there are ten.
An extraordinary feature, characteristic of all the above-mentioned animals, is the great tendency which they have to mutilate themselves, and throw their limbs about in fragments on the slightest provocation. If a specimen be handled, a certain number of fragments will assuredly be cast off. If the rays become entangled in sea-weed, or even if the water in which the animal resides happens to become impure, the same disastrous result follows, until nothing but the little circular disc remains. As a set off against this weakness, both the Ophiuræ and the Brittle-stars possess reproductive powers of a high order. Hence it not unfrequently happens that if each and all the rays of a specimen be rejected, the animal will live on, and eventually, perhaps, become a complete and perfect star-fish.
The best means of preserving an Ophiura is to let the devoted animal remain for a time expanded in sea-water, then with a small pair of forceps lift it carefully up, and plump it into a bath of cold 'fresh' water, letting it lie there for about an hour. The animal speedily dies, as if poisoned, in the fresh liquid, in a state of rigid expansion. Some writers recommend that, at this stage, the specimen should be dipped for a moment into boiling water, and then dried in a current of air; but I have never been able to detect any great benefit arising from the adoption of the process.