CRINOIDEA 621 



The Crinoidea contain nearly 500 living species, grouped in a dozen 



or more families; about 2,000 fossil species are known. 



Key to the families of Crinoidea here described: 



flj Sessile crinoids (as adults). 



6i Calyx attached directly by its base 1. Holopodidae 



6a Calyx attached by a long stalk. 



c, Stalk without or with very few cirri 2. Boukgueticrinidae 



Cj Stalk with cirri 3. Pentacrinidae 



flj Crinoids which are not sessile (as adults). 

 hi Pinnules cylindrical or somewhat flattened, with very long segments. 



4. Antedonidae 

 tj Pinnules, at least the lower, more or less prismatic, with short segments. 



5. Comastebidae 



Family 1. HOLOPODIDAE. 



All the aboral plates of the calyx fused together; calyx joined 

 directly with the sea bottom, no stalk being present ; 10 short thick arms 

 present, which curl inwards: 1 genus. 



HOLOPUS D'Orbigny. With the characteristics of the family: 1 

 species. 



H. rangi D 'Orb. Height 4 cm. : in the Caribbean Sea ; rare. 



Family 2. BOTJEGUETIC!RINIDAE. 



Calyx slender, with 5 basals and 5 radials often united, and with 

 5 or 10 arms ; stalk long, with very few or no cirri : 1 living genus. 



Rhizocrintjs Sars. Calyx elongate; 5 slender arms with long 

 pinnules; no cirri except on root of stalk: 15 to 20 species. 



R. lofotensis Sars. Arms with 30 to 40 segments, 8 cm. long; stalk 

 7 cm. long: in Atlantic Ocean, from 80 to 1,900 fathoms. 



Family 3. PENTACRINIDAE. 



Calyx small; 5 arms, each diehotomously divided 1 to 10 times, with 

 small pinnules ; stalk long, with long cirri ; no root : 4 to 5 living genera. 



ISOCRINTJS Von Meyer. Calyx with 5 basals; arms divided 3 to 5 

 times; stalk often very long, and more ^or less distinctly pentamerous 

 in cross section: 3 species in the West Indian region. 



I. asterias (L.) (Fig. 967). Length of stalk up to 48 cm., of the 

 cirri 7 cm., of the arms 10 cm. : West Indies, in 80 to 300 fathoms. 



Family 4. ANTEDONIDAE. 



Crinoids which have a stalk and are sessile only as young animals, 

 the adult having shed the stalk, except the first segment or the first few 

 segments which fuse together and bear cirri and are called the ^'centro- 

 dorsal;" 5 to 20 or more long arms, on which are pinnules: several 



