Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 Fig. 210.—Calcareous bodies from the infp;rwment of Holothu- riaus. o, calcareous wheels of Chiroduta; i, anchor with supporting plate of Synapta ; c, chair-hke bodies ; d, plates of Hulothuria impatlens ; e, hooks of Chiroduta. flattened out to form a more or less extended surface. The cylin drical form is obtained by an elongation or cue «2ii [Ilolothuroidea) (fig. 209), the round form by a shortening of the same and the penta- gonal disc by the latter process combined wit
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 Fig. 210.—Calcareous bodies from the infp;rwment of Holothu- riaus. o, calcareous wheels of Chiroduta; i, anchor with supporting plate of Synapta ; c, chair-hke bodies ; d, plates of Hulothuria impatlens ; e, hooks of Chiroduta. flattened out to form a more or less extended surface. The cylin drical form is obtained by an elongation or cue «2ii [Ilolothuroidea) (fig. 209), the round form by a shortening of the same and the penta- gonal disc by the latter process combined with a simultaneous elonga- tion of the radii. If the radii are elongated till they are two or more times the length <n2r!) b .of the inter-radii, the form takes the shape of a star (Asteroidea), which may be either flat or arched. The arms of the star may be simple processes of the disc, and en- close a part of the body cavity [Stel- leridea, Star-£sh), or they may be more independent moveable organs sharply marked ofF from the disc, and as a rule simple (Ophiuridce), but sometimes branched {Euryalidce), or they may even bear simple jointed side twigs, the jnnnulce (Crinoidea). An important characteristic of the Echinodermata is the indura- tion by calca- reous deposits of the deeper layers of the integument (dermal con- nective tis- sue), so as to give rise to a solid more or less moveable or even im- moveable ar- mour. In the leathery Holo- thuroidea (fig. 210) alone these skeletal structures are confined to isolated calcareous bodies, which are embedded in the integument, and have a definite form of latticed plates, wheels, or anchors. In these Fig. 211.—Skeletal plates of Astropecten HemprichtU (after J. MuUer). DJi, dorsal marginal ossicles ; VS, ventral marg-inal ossicles; Ap, ambulacral ossicles; Jp, in'ermediate interambulacral ossicles; Adp, anterior adambulacral ossicles projecting into the mouth.
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