This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
(465). The Star-fishes, grossly considered, might be regarded as mere walking stomachs; and the office assigned to them in the economy of nature, that of devouring all sorts of garbage and offal that would otherwise accumulate upon our shores. But, as we have already seen, their diet is by no means exclusively limited to such materials, since crustaceans, shell-fish of various kinds, and even small fishes, easily fall victims to their voracity. Delle Chiaje found a human molar tooth in the stomach of an individual which he examined. Neither is the size of the prey whereon they feed so diminutive as we might suppose from a mere inspection of the orifice representing the mouth; for not only is this extremely dilatable, but, as we have found to be the case in the Actiniae, the stomach is occasionally partially inverted, in order more completely to embrace substances about to be devoured. Shellfishes are frequently swallowed whole; and a living specimen of Chama antiquata, Linn., has been taken entire from the digestive cavity of an Asterias. It appears, moreover, that it is not necessary for testaceous mollusca to be absolutely swallowed, shells and all, to enable the Asteridae to obtain possession of the enclosed animal, as they would seem to have the power of attacking large oysters, to which they are generally believed to be peculiarly destructive, and of eating them out of their shells.
The ancients believed that, in order to accomplish this, the star-fish, on finding an oyster partially open, cunningly inserted one of its rays between the valves, and thus gradually insinuating itself, destroyed its victim 1. Modern observations do not, as far as we are aware, fully bear out the above opinion of our ancestors as to the mode in which star-fishes attack oysters, although the destruction that they cause is pretty generally acknowledged. The observations recorded by M. Eudes Deslongchamps upon this subject, however, are exceedingly curious*. As the waves had receded from the shore, so as to leave only one or two inches of water upon the sand, he saw numbers of Asterias rubens rolling in bunches, five or six being fastened together into a sort of ball by the interlacement of their rays. He examined a great number of such balls, and constantly found in the centre a bivalve mollusk (Mactra Stultorum, Linn.) of an inch and a half in length. The valves were invariably opened to the extent of 2 or 3 lines; and the star-fishes were always ranged with their mouths in contact with the edges of the valves.
* Delle Chiaje.
1 This may be gathered from Aldrovandus, who writes as follows: "Alii ostre-arum hostes sunt Stellae marinas molli crusta intecta3,vero tarn crudeliter (ut aelianus, lib. ix. cap. 22, ait) inimicae ut haa ipsas exedant et conficiunt. Ratio insidiarum quas eis moliuntur ejusmodi est. Cum testacea suas patefaciant conchas, ciim vel refrigeratione egent, vel ut aliquid pertinens ad victum incidat; ese, uno de suis sive cruribus sive radiis intra testas ostreae hiantis insito eas claudi prohibente, came implentur " (Testae, lib. iii. p. 487.) Thus likewise Oppian: - "Sic struit insidias, sic subdola fraudes Stella marina parat, sed nullo adjuta lapillo Nititur, et pedibus scabris disjungit hiantes".
(466). On detaching them from the shell which they thus imprisoned, he found that they had introduced between the valves large rounded vesicles with very thin walls, and filled with a transparent fluid. Each Asterias had five of these vesicles ranged around its mouth: but they were of very unequal size; generally there were two larger than the rest, equal in size to large filberts, while the other three were not bigger than small peas. These vesicles appeared to be attached to the Asterias by short pedicles; and at the opposite end of each was a round open aperture, through which the fluid contained in the vesicle flowed out, drop by drop. No sooner was the animal detached from the shell that it was thus sucking, than the vesicles collapsed and became no longer distinguishable. The Madras were all found to be more or less devoured, some having only their adductor muscles left; but, however little they had been injured, all had lost the power of closing their valves, and were apparently dead: nevertheless there was nothing to lead to the supposition that only dead shell-fishes were attacked; so that it is difficult to imagine how the delicate vesicles above described escaped injury from the closing of the valves.
M. Deslongchamps thinks that probably the Asterias pours into the shell a torpifying secretion, and thus ensures the death of its victim.
(467). The absorption of the nutritious portions of the food in the Echinodermata is entirely accomplished by the veins distributed upon the coats of the digestive cavities, so that the chyle resulting from digestion is at once introduced into the vessels appropriated to circulation.
(468). In Asterias, the intestinal veins form a fine vascular network, covering the stomach and the ten digestive caeca. The venous trunks derived from all these sources unite to form a circular vessel (fig. 90, e), which likewise receives branches derived from the ovaria and other sources.
(469). The circular vein thus formed, which seems to be the common trunk of the venous system, communicates with another vascular circle placed around the mouth (s), by means of a dilated vertical tube of communication (f), which, from its muscular appearance and great irritability, Tiedemann regards as being equivalent in function to a heart. The circle around the mouth (s) would seem to be arterial in its character, and branches are derived from it which supply the various viscera of the body.
* Bulletin des Sciences de M. le Baron Ferussac, vol. x. p. 296.
(470). But, besides the vessels above described, apparently so disposed as to collect and distribute the nutrient fluids, there is another set of canals appropriated to the supply of the numerous vesicles connected with the locomotive suckers (§ 456); these Tiedemann regards as being totally unconnected with the vascular system properly so called, and considers the fluid contained in them as quite of a different nature. Delle Chiaje, on the contrary, asserts that the two sets of vessels are derived from each other, and describes a peculiar apparatus connected with them as performing an important part in effecting the protrusion of the suckers.