CHAPTER IX. 



THE PELMATOZOA CYSTIDEA. 1 



GRADE A. PELMATOZOA, LEUCKART (1848) 

 ( = CRINOIDEA, sensu lato Auctt.). 



CLASS I. CYSTIDEA. 



II. BLASTOIDEA. 



III. CRINOIDEA. 



IV. EDRIOASTEROIDEA. 



ECHINODERMA with the viscera enclosed in a calcified and plated 

 theca, of which the oral surface is uppermost, and which is usually 

 attached, either temporarily or permanently, by the aboral surface. 

 Food brought to the mouth by a subvective system of ciliated 

 grooves, radiating from the mouth either between the plates of the 

 theca (endothecal), or over the theca (epithecal), or along processes 

 from the theca (exothecal : arms, pinnules, etc.), or, in part, and 

 as a secondary development, below the theca (hypothecal). Anus 

 usually in the upper or oral half of the theca, and never aboral. 

 An aborally placed motor nerve-centre gives off branches to the 

 stroma connecting the various plates of the theca and of its 

 brachial, anal, and columnar extensions, and thus co-ordinates the 

 movements of the whole skeleton. The circumoesophageal water- 

 ring communicates indirectly with the exterior ; the podia, when 

 present, are respiratory, not locomotor, in function. 



The origin and meaning of many of these characters have 

 already been discussed in the general section. The origin of 

 others will be traced in following the history of the Grade ; and 

 many of them will be more fully discussed under Crinoidea, in 

 which class alone are they adequately known. 



The classes of Pelmatozoa here adopted are of very unequal 



1 By F. A. Bather, M.A. Since the majority of Pelmatozoa, being of extinct 

 types, present peculiar difficulties, the student unfamiliar with Echinoderm structure 

 is recommended to begin either with the description of a simple Crinoid (Chapter XL), 

 or that of a Starfish (Chapter XIV.). 



