NO. 19.] ECHINODERMS OF CONNECTICUT. 129 



are at first somewhat similar to those of the starfish, and are 

 termed auricularicr. In the later stages, the • embryos of many 

 species become barrel-shaped. 



After swimming and feeding at the surface for several weeks 

 the embryo settles to the bottom and transforms itself into a 

 young holothurian. 



In a few species from other parts of the world, the young 

 develop within the body cavity of the parent. 



KEY TO SPECIES 



The class Holothuroidea is conveniently divided into two 

 orders, based on the characters of the water-vascular system and 

 the distribution of pedicels: — (i) the Actinopoda, in which 

 the radial canals of the water-vascular system are well developed 

 and supply the oral tentacles, and (2) the Par actinopoda, in 

 which the radial canals and pedicels are absent, the oral tenta- 

 cles being supplied from the circumoral canal. The first order 

 includes our species of Cucumaria and Thyone, and the second 

 order includes the two species of Synapta, 



The following key will serve to distinguish our native species : 



1. Pedicels present; body not very slender 2 



Pedicels wanting; body slender and worm-like 5 



2. Pedicels scattered over the whole body 3 



Pedicels mainly limited to the five ambulacral regions; body 



whitish Cucumaria pulcherrima 



3. Ventral ambulacral area conspicuously demarcated by a dis- 



tinct border free from pedicels; color white, yellowish 



white, or flesh-color Thyone unisemita 



Ventral ambulacral area not conspicuously demarcated; 

 pedicels very numerous all over body; color brown or 

 black 4 



4. Body tapering posteriorly, but not attenuated; pedicels del- 



icate ; few calcareous plates in body wall. Thyone briareus 



Body attenuated posteriorly; pedicels and body wall rough 



from closely crowded calcareous plates . . . Thyone scabra 



5. Color white or yellowish ; the five radial plates of calcareous 



ring perforated for passage of nerve . . Synapta inhaerens 



Color reddish or pink; radial plates of calcareous ring 



notched in anterior border Synapta roseola 



