Sub-Kingdom III. ECHINODERMATA 
To the Echinoderms belong radially or bilaterally symmetrical animals, which 
were formerly included with the Coelenterates under the general category of 
Radiata ; but were recognised by Leuckart as the representatives of a distinct 
animal type. They possess a well-developed, usually pentamerous dermal 
skeleton, which is composed of calcareous plates, or of minute, isolated, cal- 


~ SS 
ie yg 
SAS Bo sine 
a, Magnified cross-section of an 
Echinoid spine; Fiji Islands. b, Mag- 
nified section of coronal plate of a 
recent Sea-urchin (Sphaerechinus) ; 
plane of section parallel to surface. 
Ee yee 


Fia. 218. 
Pentacrinus subteres, Goldf. Upper Jura; Reichen- 
bach, Wurtemberg. «, Vertical section of stem-joint in 
plane indicated inc. 18/;; 6, Transverse section of 
same. 18/,;; c, Joint-face; d, Side view of column 
(natural size). 
careous bodies embedded in the integument ; the exoskeleton may be more or 
less movable, or even immovable, but is very frequently provided with moye- 
able appendages (spines, bristles, pedicellariae, ete.) The arrangement both of 
the skeletal parts and of the principal organs is so generally pentamerous, that 
five may be regarded as the fundamental numeral pervading the whole sub- 
kingdom of Echinoderms. 
