ECHINODERMA — BLASTOIDS. 
G7 
internal organs ; hence these folds are called hydrospires 
(water-breathers). In most blastoids the theca is borne on 
a stem and shows conspicuous five-rayed symmetry. In 
a few forms, however, the theca rested on the sea-floor, and 
tliis produced irregularity in its shape with a change in one 
of the food-grooves ; examples of this are Eleutkcrocrinus, 
Pcntephylhim, and Zygocrinus, which in other respects are 
dissimilar and not closely related. 
The preceding Classes are essentially fixed forms, living 
with tlie mouth upwards and obtaining food by means of a 
cm-rent 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 
udthout the lielp of ciliated grooves. In the Telmatozoa 
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 tlie body 
(calyx or theca). 
Class EDRIOASTEROIDEA. 
covering 
plates - 
flooring 
...plates 
mouth 
We come now to a Class of Echinoderma, still liviu" in 
the manner of Pelmatozoa, but uith the food-grooves directly 
floored by thecal plates 
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 inler- 
of them, such as Agda- 
crmus and Lepiaodiscus, ' anus 
were probably fixed for 
the whole of their exist- 
ence, usually to some Fig. 31 . — Edrwaster Bigsbyi. Seen from 
large shell. In these above. The covering-plates are removed 
genera no pores have remain on the other 
been found between the 
'C^unzier-pore 
'pores in 
food- groove 
two. (After Bather.) 
flooring-plates of the groove. Others, such as Edrioastcr 
(Fig. 31) and Dinocystvi, could probably shift their positions. 
Gallery 
VIII. 
Table-case 
30. 
Table-ease 
30. 
