They differ from the Star-fishes in having the disk entirely distinct from the arms; that is, the arms, instead of merging gradually into the disk, start at once from its margin. They have no interambulacral spaces or plates; but the whole upper surface is formed of large hard plates, which extend from the back over the sides of the arms to their lower surface, where they form a straight ridge along the centre. ([Fig. 149.]) The sides of these plates are pierced with holes, through which the tentacles pass; these have not, like those of the Star-fishes and Sea-urchins, a sucker at the extremity, but are covered with little warts or tubercles ([Fig. 150]); they are their locomotive appendages, and their way of moving is curious; they first extend one of the arms in the direction in which they mean to move, then bring forward two others to meet them, three arms being thus usually in advance, and then they drag the rest of the body on. They move with much more rapidity, and seem more active, than the Star-fishes; probably owing to the greater independence of the arms from the disk. The spines project along the margin of the arms, and not over the whole surface, the back of the arms being perfectly free from any appendages, and presenting only the surface of the plates. The madreporic body is formed by a plate on the lower side of the disk, in a position corresponding to that which it occupies in the young Star-fish; this plate is one of the large circular shields occupying the interambulacral spaces around the mouth. ([Fig. 149.]) On each side of the arms, where they join the disk, are slits opening into the ovarian pouches. They have no teeth; but the hard ridge at the oral end of the ambulacra, extending toward the mouth in Star-fish, is still more distinct and sharper in the Ophiurans, approaching more nearly the character of teeth.
| Fig. 149. One arm of Fig. 148; from the mouth side. | Fig. 150. Ambulacral tentacle of Ophiopholis; magnified. |
Astrophyton. (Astrophyton Agassizii Stimp.)
A singular species of Ophiuran, known among fishermen as the "Basket-fish," ([Fig. 151,]) is to be found in Massachusetts Bay. Its arms are very long in comparison to the size of the disk, and divide into a vast number of branches. In moving, the animal lifts itself on the extreme end of these branches, standing as it were on tiptoe ([Fig. 151]), so that the ramifications of the arms form a kind of trellis-work all around it, reaching to the ground, while the disk forms a roof. In this living house with latticed walls small fishes and other animals are occasionally seen to take shelter; but woe to the little shrimp or fish who seeks a refuge there, if he be of such a size as to offer his host a tempting mouthful; he will fare as did the fly who accepted the invitation of the spider. These animals are exceedingly voracious, and sometimes, in their greediness for food, entangle themselves in fishing lines or nets. When disturbed, they coil their arms closely around the mouth, assuming at such times a kind of basket-shape, from which they derive their name.
This Basket-fish is honorably connected with our early colonial history, being thought worthy, by no less a personage than John Winthrop, Governor of Connecticut, who, as he says, "had never seen the like," to be sent with "other natural curiosities of these parts" to the Royal Society of London, in 1670. He accompanies the specimen with a minute description, omitting "other particulars, that we may reflect a little upon this elaborate piece of nature." His account is as graphic as it is accurate, and we can hardly give a better idea of the animal than by extracting some portions of it. "This Fish," he says, "spreads itself from a Pentagonal Root, which incompasseth the Mouth (being in the middle), into 5 main Limbs or branches, each of which, just at issuing out from the Body, subdivides itself into two, and each of these 10 branches do again divide into two parts, making 20 lesser branches; each of which again divide into two smaller branches, making in all 40. These again into 80, and these into 160; and these into 320; these into 640; into 1280; into 2560; into 5120; into 10,240; into 20,480; into 40,960; into 81,920; beyond which the further expanding of the Fish could not be certainly trac'd";—a statement which we readily believe, wondering only at the patience which followed this labyrinth so far.
In a later letter, after having had an interview with the fisherman who caught the specimen, and, as he says, "asked all the questions I could think needful concerning it," the Governor proceeds to tell us that it was caught "not far from the Shoals of Nantucket (which is an Island upon the Coast of New England)," and that when "first pull'd out of the water it was like a basket, and had gathered itself round like a Wicker-basket, having taken fast hold upon that bait on the hook which he" (the fisherman) "had sunk down to the bottom to catch other Fish, and having held that within the surrounding brachia would not let it go, though drawn up into the Vessel; until, by lying a while on the Deck, it felt the want of its natural Element; and then voluntarily it extended itself into the flat round form, in which it appear'd when present'd to your view." The Governor goes on to reflect in a philosophical vein upon the purpose involved in all this complicated machinery. "The only use," he says, "that could be discerned of all that curious composure wherewith nature had adorned it seems to be to make it as a purse-net to catch some other fish, or any other thing fit for its food, and as a basket of store to keep some of it for future supply, or as a receptacle to preserve and defend the young ones of the same kind from fish of prey; if not to feed on them also (which appears probable the one or the other), for that sometimes there were found pieces of Mackerel within that concave. And he, the Fisherman, told me that once he caught one, which had within the hollow of its embracements a very small fish of the same kind, together with some piece or pieces of another fish, which was judged to be of a Mackerel. And that small one ('tis like) was kept either for its preservation or for food to the greater; but, being alive, it seems most likely it was there lodged for safety, except it were accidentally drawn within the net, together with that piece of fish upon which it might be then feeding." The account concludes by saying, "This Fisherman could not tell me of any name it hath, and 'tis in all likelihood yet nameless, being not commonly known as other Fish are. But until a fitter English/ name be found for it, why may it not be called (in regard of what hath been before mentioned of it) a Basket-Fish, or a Net-Fish, or a Purs-net-Fish?" And so it remains to this day as the Governor of Connecticut first christened it, the Basket-fish.