Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 OIIINOIDEA. 289 tacrhms form [P. Europ(tus) (fig. 233), consists of a complicated metamoi' The greater number of Crinoids belong to the oldest periods of the Jiistory of the earth (the Cambrian, Silurian, Devonian, and the Cavbonifer-ous formations). Existing forms live mostly at considerable depths. We distinguish two orders, the Tesselata and the Articulata. The latter is represented by numerous fossil forms, bvit by only a few living genera as Penta- crinus, Il
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 OIIINOIDEA. 289 tacrhms form [P. Europ(tus) (fig. 233), consists of a complicated metamoi' The greater number of Crinoids belong to the oldest periods of the Jiistory of the earth (the Cambrian, Silurian, Devonian, and the Cavbonifer-ous formations). Existing forms live mostly at considerable depths. We distinguish two orders, the Tesselata and the Articulata. The latter is represented by numerous fossil forms, bvit by only a few living genera as Penta- crinus, Ilolojms, and Comctula (fig. 234). The cup is always less completely provided with plates than in the fossil Tesselata. Articulata. Fam. Peatacrinidae. Crinoids with ten arms, several times bifurcated. There is a pentagonal stalk with whorled cirri. Pcutaerlmis caput Mcdvscr, Mill, from the Antilles. P. Miilleri Oerst., West Indian Ocean. The fossil forms are : Encrinits liliiformis Schl. (fig. 234) from the Muschelkalk ; also A2Jiocrimis, allied to the ! i existing Rliizocrimis lofotensis Sars, and to Batliycrinnx 'â /<SjA <jraeil/x, and aldrieliiamis W. Th., from the deep sea. ^^ Allied to this group is the third existing genus Holopvs, X^iV from the West Indies, with calj'x attached by a short âE'C/'(«»s?i7ii- unjointed prolongation of its apex. H. Pangii d'Orb. Fam. Comatulidae. Stalked only in the young state. The adult animal is free. There are usually ten arms at the margin of the flattened body ; mouth and anus are present. The Coma' tulidce possess the power of striking their arms towards the ventral surfacfi and. so of propelling themselves amidst the sea-weeds. The vermiform larva, with its four ciliated girdles, makes its appearance within the egg-membranes. It acquires a mouth and anus, also a tuft of cilia at the posterior end of the body, and swims about freely. It passes later, by the formation of cal- careous rings and rows of plates, into t
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