. Animal biology. Zoology; Biology. PHYLUM ECHINODERMATA 205 5. Crinoidea (kri noi'de a; F., krinon, lily, and eidos, form).—The feather stars and sea lilies. 236. Asteroidea.—The general characteristics of this class are illus- trated by the starfish. The bases of the rays take up the entire circum- ference of the disc and thus are not definitely marked off from it. The number of rays varies in different species from 5, which is the most usual number, to more than 40. Though usually an odd number, it is not. Fig. 117.—The long-armed brittle or serpent star, Amphiodia occidental is (Lyman), oc
. Animal biology. Zoology; Biology. PHYLUM ECHINODERMATA 205 5. Crinoidea (kri noi'de a; F., krinon, lily, and eidos, form).—The feather stars and sea lilies. 236. Asteroidea.—The general characteristics of this class are illus- trated by the starfish. The bases of the rays take up the entire circum- ference of the disc and thus are not definitely marked off from it. The number of rays varies in different species from 5, which is the most usual number, to more than 40. Though usually an odd number, it is not. Fig. 117.—The long-armed brittle or serpent star, Amphiodia occidental is (Lyman), occurs along the Pacific Coast from California to Alaska. It may voluntarily part with one or more arms—this is autotomy—and regenerate new ones readily. {Drawn by Robert Allen Wolcott.) invariably such, since there are forms in which the number is regularly six. In some the disc is small and the rays are long and slender; in others the disc is large and the rays short and broad. This shortening and broadening of the rays may go so far as to produce pentagonal types. Starfishes are rather generally distributed, being absent only from the polar regions. 237. Ophiuroidea.—This class differs from the preceding in that it possesses slender rays sharply marked off from the disc and in that the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wolcott, Robert Henry, 1868-1934; University of Nebraska (Lincoln campus). Dept. of Zoology. New York ; London : McGraw-Hill Book Company, Inc.
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