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- 





FIG. 211 



, Magnified cross - section of an 

 Echinoid spine ; Fiji Islands. &, Mag- 

 nified section of coronal plate of a 

 recent Sea - urchin (Sphaerechinus) ; 

 plane of section parallel to surface. 



218. 



Pentacriims snlteres, Goldf. Upper Jura ; Reichen- 

 bacli, Wurteinberg. c, Vertical section of stem-joint in 

 plane indicated in c. 18/] ; ?>, Transverse section of 

 same. 18/j ; c, Joint -face; </, 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 move- 

 able appendages (spines, bristles, pedicellariae, etc.) 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. 



