Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 296 ECHINODERMATA. lacral branchiae upon a rosette formed of large pores on the dorsal surface (fig. 239). The locomotive feet are very small in Clypeastridce, and are distributed either over the whole surface of the ambulacra, or are confined to branching rows upon the ventral surface. In the Spatangidce there are peculiar bands upon the upper surface, the fascioles or semitce (fig. 239), upon which, in place of the spicules, knobbed bristles with active cilia (davulce) are distributed.
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 296 ECHINODERMATA. lacral branchiae upon a rosette formed of large pores on the dorsal surface (fig. 239). The locomotive feet are very small in Clypeastridce, and are distributed either over the whole surface of the ambulacra, or are confined to branching rows upon the ventral surface. In the Spatangidce there are peculiar bands upon the upper surface, the fascioles or semitce (fig. 239), upon which, in place of the spicules, knobbed bristles with active cilia (davulce) are distributed. Develop- ment takes place with a Pluteus larval stage, in which the larva is provided with ciliated epaulettes or with an apical rod. The Sea-urchins live, as a rule, near the coast, and feed on molluscs, small marine animals, and Fuci. Some species of Echinus have the power of boring holes in the rocks in which they live. We find many fossil shells, especially in the chalk. FIG. 239.—Sringopsin lynfera with the fascioles or Semites surround- ing the rosette. A, anus. Order 1.—CIDARIDEA=REGULAR SEA-URCHINS. Echinoidea with central mouth and equal band-like ambulacra ; with teeth and masticatory apparatus ; with sub-central anus in the apical space. Fam. Cidaridae. With, very narrow ambulacra! and broad interambulacral areas, on both of which are large perforated tubercles and club-shaped spines. There arc no oralbranchise. Cidaris mi'tularia Lain., Phylla fan-thus imperlal'ns East Indies. Fam. Echinidae. Sea-urchins. The pores are grouped in transverse rows ; there is a round, thin shell, broad ambulacra! spaces bearing tubercles and spines, which are mostly short and pear-shaped. Oral branching arc present. nc-ustcs varlegat-Hx, Echinus mclo Strongylocentrotus llvidvs Brit. Lin., Mediterranean. Fam. Echinometridae. With long oval shell, imperforate tubercles and oral branchiae. Ecliinometra oblong a Blainv., Podoplwra atrata
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