Outlines of zoology . hurinse have flexible tests and powerful Asthenosoma and III. Irregularia. The anus lies outside the apical systemof plates in the posterior inter-radius. the heart-urchins, Spatangus and Echinocardium, withoutlanterns. In the related Echinoneus there is a lantern in theyoung forms. It is interesting to contrast the large massiveClyfeasier with the minute Echinocyamus pusillus, commonin the stomach of cod-fishes. 268 PHYLUM ECHINODERMA. Class HoLOTHUROiDEA. Sea-Cucumbers Cylindrical or worm-like Echinoderms, elongated in thedirectio
Outlines of zoology . hurinse have flexible tests and powerful Asthenosoma and III. Irregularia. The anus lies outside the apical systemof plates in the posterior inter-radius. the heart-urchins, Spatangus and Echinocardium, withoutlanterns. In the related Echinoneus there is a lantern in theyoung forms. It is interesting to contrast the large massiveClyfeasier with the minute Echinocyamus pusillus, commonin the stomach of cod-fishes. 268 PHYLUM ECHINODERMA. Class HoLOTHUROiDEA. Sea-Cucumbers Cylindrical or worm-like Echinoderms, elongated in thedirection of the main axis, with more or less tendency tobilateral symmetry, with a usually soft or leathery skin, withirregularly scattered microscopic calcareous bodies, with aterminal mouth surrounded by tentacles, with a posterior anus,with or without tubefeet, with no external madreporite, witha muscular body wall. The Holothurians do not at first sight suggest the otherEchinoderms, for they are like plump worms, and the. Fig. 138.—Spicules of Holothurians.—After Semon. The series /-6 shows stages in the development of an anchor and a platein a Synapia. The series j^~E shows stages in the development ofa wheel in Ckiridota, a Synaptid. calcareous skeleton is not prominent. But closer examina-tion shows the characteristic pentamerous symmetry, andthe occurrence of calcareous plates in the skin. Theseseem to be absent in the unique pelagic Pelagothuria. Holothurians occur in most seas, from slight to verygreat depths. Their food consists of small animals, and oforganic particles from the sand. Some of them catch thesein their waving tentacles, which are then plunged into thepharynx. The muscles of a captured Holothurian oftenover-contract and eject the viscera at the ends or through HOLOTHVROIDEA. 265 a side rupture; in this way the animal may sometimesescape, and the viscera can be regrown. In Synapta the rapture of the body takes place very rapidly, and isprobably defensive, t
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
