PENTACRINUS ASTERIA (CAPUT MEDUSA) 



Miiller 



Material. This beautiful crinoid is found in the West 

 Indies in depths over eighty fathoms. It is too expensive for 

 class work and the description given here is merely for compari- 

 son and completeness. 



Descriptive Part 



Pentacrinus Asteria is a representative of the Class Crinoidea. 

 Its body is divided into a long stalk or peduncle and a chalice 

 with arms. The stalk is composed of numerous pentagonal 

 columnal ossicles with toothed anterior and posterior edges and 

 so articulated that the teeth of one columnal ossicle fit into the 

 spaces between the teeth of the next columnal ossicle. In the 

 centre of each ossicle is a canal running through the entire stalk. 

 Situated on the stalk at more or less regular intervals are the 

 cirri. Those nearest the chalice are the shortest. There are 

 always five cirri for each vorticellum. The columnal ossicle 

 bearing the cirri is somewhat larger than the intermediate 

 ossicles and has five articular facets for the reception of the cirri. 

 The cirri are many-jointed and have a central longitudinal canal 

 communicating with the canal of the stalk, and through this 

 with the canals of the arms. The first columnal ossicle of the 

 stalk is star-shaped with the rays of the star situated in the 

 interradii of the animal and appearing on the surface as small 

 rounded plates between the bases of the arms. This star-shaped 

 first columnal ossicle serves as base for the chalice and can be 

 seen on removal of the stalk. The chalice is composed of the 

 arms and the disc. Each arm has three radial joints beyond 

 which begins the splitting up of the arm into branches. Al- 



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