62 BRANCH ECHINODERMATA 



They are probably excretory organs also, and are connected 

 with the manipulations of the tentacles.^ 



Multiplication is generally similar to that of the starfish, 

 except in rare cases of hermaphroditism. There are also cases 

 recorded of the female caring for her brood in dorsal pouches. 

 In unfavorable conditions they void the whole viscera and yet 

 live and replace the lost parts. ' 



In the development from the bilateral larva to the radial 

 adult there is a marked metamorphosis. 



Several species are hosts for certain parasites. A small 

 fish infests the cloaca and branchial trees of one or two species. 

 A snail lives in one species and a mussel in another. 



Use. — They are used for food by the Malays, who call them 

 " trepang," and use them principally for soups. Millions of 

 them are captured in the south seas, where hundreds of vessels 

 are engaged in the trepang fisheries. 



Distribution. — Holothurians are widely distributed, being 

 found from the arctic to the tropical regions. 



Geologically, they date from the Carboniferous Period. 



CLASS V. CRINOI'DEA 



Crinoids are fixed echinoderms with a flexible stem or stalk 

 of calcareous perforated disks, bearing a flower-like body at 

 the top of the stem (Fig. 48). This body consists of a cup- 

 shaped center bearing five or ten arms, usually branched. 

 The " feather stars," found at a less depth, later become de- 

 tached and float around in the water. 



Ambulacral Grooves. — Five ciliated ambulacral grooves 

 (Fig. 49) extend from the mouth out on the arms and their 

 branches, and give off branches to the pinnules. They serve 

 as channels through which the food passes to the mouth, and also 

 for the purpose of respiration. 



Food. — They feed on small crab-like animals and on marine 

 unicellular animals and plants. 



The nervous system consists of a nerve ring surrounding the 

 mouth, and given off from this nerve ring are a series of amliu- 

 lacral nerves which extend the entire length of the arms and 

 pinnules. 



1 Parker and Haswell's "Zoology," vol. i, p. 372. ^ ibjd., p. 400. 



