Star Fish, the popular name of the radiated animals of the class of echinoderms and the order asterioids, well exemplified by the common species of the New England coasts, the five-fingered Jack of the sailors. The quinary arrangement prevails to a remarkable extent in the star fishes. The body is depressed, and divided into rays like a star; the upper surface is studded with rough knobs, varying in color with the species, but generally reddish or yellowish, between which are the openings of many very minute tubes for the passage of water in and out of the body; the skin is coriaceous, and contains the above named corpuscles, beneath which is a cutaneous skeleton of porous calcareous pieces, movably articulated, and extending on the lower surface from the mouth in the centre to the end of the rays. In the lacunae between these pieces are the am-bulacral pores, along the centre of the lower surface of each ray, through which are protruded the ambulacral tubes; these are the principal organs of locomotion, are arranged in a double or quadrangular row, and are provided with contractile sacs or vesicles on the inner surface of the envelope; the tubes are constantly in motion, each ending in a suctorial disk, and pull the animal along as by the successive action of so many little anchors.
On the external edges of the rays are series of stiff spines, probably serving for protection, and at the end of each ray is a small reddish eye speck; there are also scattered over the upper surface small processes ending in calcareous hooks or pincers. The mouth opens into the stomachal cavity, from which branching caecal tubes extend to the extremity of each arm; they have no long tentacles like the sea anemone (actinia), but the stomach can be everted over their food and then be turned back again; the mouth is very dilatable, and will admit large mollusks with the shell, the hard parts being ejected after the soft portions are digested. There is great variety in the spreading, division, and subdivision of the arms, and in the relative size of the central disk, but all are arranged after the radiated plan; the rays can be bent in any direction, according to the will of the animal, by the contractile skin and muscles. The slender ophiurans progress by the undulatory movements of the rays, which, when very slender, long, and branching, have no eyes at the tips; there is generally no anal aperture, and if any it is on the dorsal surface.
By the action of cilia water flows through the body, through the aquiferous system, distending and protruding the ambulacral feet, filling the circular vessel around the mouth, and serving for respiration, which, according to Siebold, is performed partly by the vesicular appendages attached to the central ring; all the viscera are bathed in water, and respiration is also effected through the delicate blood vessels thereon distributed. The vascular system is very simple; the nervous ganglia are five, arranged around the mouth, each sending filaments to the arm at whose base it lies; the sense of touch is very acute. According to Sars, Steen-strup, and Lutken, there is not only in this class a great power of regeneration of lost parts, but a spontaneous division of the disk itself, with regeneration of the necessary portions, several times repeated up to a certain age, for the multiplication of the individual. While this may sometimes be a simple division, in many it is the normal mode of multiplication instead of gemmation. This form of agamic multiplication in ophiuroids and asterioids has been called schizogeny.
On the upper surface, to one side of the centre and between two of the arms, is a round bright-colored spot, the madreporic plate or body, communicating with a canal leading to the water vessel around the mouth - a supposed filter for water passing into the aquiferous system and through the body. They propagate usually by eggs, and the sexes are in separate individuals; the larvae are at first oval, ciliated bodies, from which the radiated perfect animal is developed, at various stages of its growth, by a process of internal gemmation. The crinoid comatula, or feather star, free when adult, has its young attached on a long slender stem; Sars has traced the growth of echinaster from a spheroidal free-moving mass to the perfect star fish. Some species secrete a reddish fluid on the surface, probably the coloring matter, often irritating to the skin of persons handling them; according to Deslong-champs, they can inject a fluid into the shells of their victims, which stupefies and renders them an easy prey.
Rymer Jones says star fishes may be considered as mere walking stomachs, their office in the economy of nature being to devour all kinds of garbage which would otherwise accumulate on the shores; they eat also living crustaceans, mollusks, and even small fish, and are believed to be very destructive to oysters; they are not used as food by man, but are in many places highly esteemed as manure. - For a popular account of the British species, see "History of British Starfishes," by Edward Forbes (London, 1841). For the New England species, see the recently published works of Agassiz. The common star fish of the North American coast (asterias rubens, Lam.), generally considered the same as the European species, is too well known to need description; the colors vary from reddish to yellowish, and the diameter from an inch to more than a foot. - The star fishes are found from the Trenton limestone of the lower Silurian epoch down to the present time.
Common Star Fish (Asterias rubens).