ANNULOIDA. 



CHAPTER XII. 



CRINOIDEA, CYSTOIDEA, AND BLASTOIDEA. 

 ORDER IV. CRINOIDEA. 



THE Crinoids or Sea-lilies are Echinodermata in which the body 



is fixed, during the whole or 

 a portion of the existence of 

 the animal, to the sea-bottom 

 by means of a longer or shorter 

 jointed or flexible stalk. The 

 body is provided with solid 

 arms which are primarily 

 five to ten in number, are 

 independent of the visceral 

 cavity, and are grooved on 

 their upper surface. The 

 arms are furnished with lat- 

 eral processes or " pinnulce," 

 and the reproductive organs 

 are lodged beneath the integu- 

 ment on the ventral surf ace of 

 these, and are not placed in 

 the body-cavity. 



If we take such a living 

 Crinoid as Rhizocrinus (fig. 

 72), we shall be able to ar- 

 rive at a comprehension of 

 the leading characters of this 

 order. Rhizocrinus is one 

 of those Crinoids which is 

 permanently rooted to some 

 foreign object by the base 

 of a stalk which is composed 

 of a number of calcareous 

 pieces or articulations. In 

 some cases (as in Apiocrinus, 

 fig. 81), the base of the stem 

 or " column " is consider- 

 ably expanded. In other 

 cases the column is simply 

 " rooted by a whorl of ter- 

 minal cirri in soft mud " (Wyville Thomson). The joints of 

 the column are movably articulated to one another, the joint- 



Fig. 72. Crinoidea: Rhizocrinus Lofoten- 

 sis, a living Crinoid (after Wyville Thomson), 

 four times the natural size, a Stem ; b Calyx ; 

 c c Arms. 



