1/ 



Vol. 5, p. 27-33, pi. 3. August 18, 1922 



Occasional Papers 



OF THE 



Boston Society of Nat 



THE ASCIDIAN AMAROVCIVM 



A VALID SPECIES. 



By CASWELL GRAVE. 



The conclusion is reached by Van Name (1910) as the result 

 of his study of Amaroucium pellucidum (Leidy, 1855) and A. con- 

 stellatum (Verrill, 1871) (compound ascidians), that they constitute 

 a single species to which Leidy's name, pellucidum should be 

 applied. He proposes, however, since the species regularly occurs 

 in two dissimilar forms, that Verrill's species be distinguished as 

 A. pellucidum, form constellatum. 



This conclusion is accepted as valid by Sumner, Osburn and 

 Cole (1913) but, in their report, they list and treat VerrilFs species 

 independently of A . pellucidum although under the name proposed 

 by Van Name, A. pellucidum, form constellatum. 



In the course of my studies of the tadpole larvae of the ascidians 

 of the Woods Hole region, however, it was noted that the larvae 

 of A. pellucidum and of A. constellatum differ consistently in size, 

 structure, and behavior and that the differences between them 

 are of a nature and magnitude such as to give them specific value. 



The object of this paper is to call attention to these differences 

 in the larval forms of the two species; to differences also in the 

 adult forms; to show that the species A. constellatum of Verrill 

 should not be merged with Leidy 's A. pellucidum; and to empha- 

 size the fact that no species can be completely or satisfactorily 

 described in the absence of a knowledge of its complete life history, 

 especially if a larval form is present. The larval form is just as 

 truly the species as is the adult and in many cases, as in tunicates, 

 parasitic copepods, barnacles and other forms considered to be 

 degenerate, it attains a higher grade of organization than is found 

 in the adult condition. 



The observation made by Van Name and by Sumner, Osburn 

 and Cole, that led them to consider A. constellatum (Verrill) as a 



