ECHINODEEMA — BLASTOIDS. 



67 



internal organs ; hence these folds are called hydrospires Gallery 

 (water-breathers). In most blastoids the theca is borne on VIII. 

 a stem and shows conspicuous five-rayed symmetry. In Table- ease 

 a few forms, however, the theca rested on the sea-floor, and 

 this produced irregularity in its shape with a change in one 

 of the food-grooves ; examples of this are Eleiitlierocrinus, 

 Pentephyll'iom, and Zygocrinus, which in other respects are 

 dissimilar and not closely related. 



The preceding Classes are essentially fixed forms, living 

 with the mouth upwards and obtaining food by means of a 

 current of sea-water swept towards the mouth along ciliated 

 food-grooves. They are therefore termed PELMATOZOA 

 (stalk animals) in opposition to the ELEUTHEROZOA (free- 

 moving animals) such as star-fish and sea-urchins, which live 

 with the mouth downwards and take more solid food into it 

 without the help of ciliated grooves. In the Pelmatozoa 

 hitherto discussed the food-grooves are supported on special 

 structures usually stretched out from the body ; and exten- 

 sions from the hydraulic system may pass along these 

 appendages, but do not penetrate the plated wall of the body 

 (calyx or theca). 



Class EDRIOASTEROIDEA. 



We come now to a Class of Echinoderma, still living in Table-case 

 the manner of Pelmatozoa, but with the food-grooves directly 

 floored by thecal plates 



coueri 

 Jdlates - 



flooring 

 .plates 

 mouth 



and in some cases at least 

 with pores between those 

 flooring-plates, giving 

 passage, it is supposed, 

 to extensions from the 

 hydraulic system. These 

 are the Edrioasteroidea 

 (sessile star-fish). Some intei 

 of them, such as Agela- Ifj^^^y 

 crinus and Lepidodisms, ' ani^s 

 were probably fixed for 

 the whole of their exist- 

 ence, usually to SOme.FiG. Sl.—Edrioaster Bigshyi. Seen from 

 large shell. In these above. The covering-plates are removed 

 o-Pn pra n n " i^nrp^ h a vp ^^^^ ^^y^' remain on the other 



genera no pores nave ^^^^ (After Bather.) 

 been found between the 



flooring-plates of the groove. Others, such as Edrioaster 

 (Fig. 31) and Dinocystis, could probably shift their positions, 



F 2 



\UHLter-pore 

 ^ pores irt 

 food- groove 



