THE PARASITIC ISOPOD LEIDYA DISTORT A (LEIDY) 

 FOUND ON A NEW HOST. 



By Harriet Richardson, 

 Collaborator, Division of Marine Invertebrates, U. 8. National Museum. 



Prof. A. E. Verrill has recently sent me specimens from the Ber- 

 muda Islands of Pachygrapsus trans versus (Gibbes), infested with 

 an Isopod parasite. The parasite is located in the branchial cavity 

 of the host. On examination the Isopod was found to be Leidya dis- 

 torta (Leidy), heretofore recorded as parasitic on Vca pugilator 

 (Bosc). This genus and species is therefore not confined to one 

 genus and species of host. 



The species found by Fritz Mueller in the branchial cavity of a 

 Grapsoid Pachygrapsus transversus (Gibbes), from the coast of 

 Brazil, is probably this species and genus, and not Grapsicepon 

 fritzii, the nominal species of Giard and Bonnier. a 



Because Grapsicepon edwardsi was found on a Grapsoid, Planes 

 minutus, according to the theory advanced by these authors the para- 

 site of another Grapsoid of the same family, Pachygrapsus trans- 

 versus, would naturally be a Grapsicepon. The facts prove, however, 

 that this is not always the case, in this instance as in other parasitic 

 Isopod genera before cited. 



Leidya is found parasitic on both Ilea and Pachygrapsus, two 

 widely separated genera of hosts belonging to different families. 



As no descriptions or figures of this form have been given since 

 those published by Leidy, the following descriptions and figures may 

 be of interest, in that the young female is also described and figured 

 for the first time : 



a Trav. dn Labor, de Wimereux, V, 1887, p. 70, and VIII, 1900, p. 226. 



Proceedings U. S. National Museum, Vol. XXXIV— No. 1593. 



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