Proce dines’ “ot 
the United States 
National Museum 
SMITHSONIAN INSTITUTION + WASHINGTON, D.C. 
Volume 125 1968 Number 3668 
The Genus Pterodrilus 
(Annelida: Branchiobdellida) 
—_——_—.. _—__——— 
By Perry C. Holt? 
Visiting Research Associate 
Department of Invertebrate Zoology 
The branchiobdellid worms, once greatly neglected, have received 
somewhat more attention in recent years. Occurring as epizoites on 
freshwater decapods and, in a few cases, on other crustaceans of the 
Northern Hemisphere, their distribution, evolution, and relationships 
with their hosts furnish several interesting problems. In spite of 
increased interest in them, however, the systematic account of no 
genus of North American branchiobdellids is at a stage adequate for 
a satisfactory consideration of many of these broader problems. 
Such is the case for the genus Pterodrilus, whose members form a 
distinctive part of the branchiobdellid fauna of eastern North America. 
In the last 20 years, however, I have gathered together a large num- 
ber of specimens of the previously known species of the genus plus 
material representing five new species. 
It is now possible, therefore, to present a more nearly adequate 
definition of the genus, redescriptions and new distributional data 
for the previously described species, descriptions of the new species, 
and a discussion of the evolutionary and geographical relationships 
of the genus. These are the objectives of the present paper. 
1 Department of Biology, Virginia Polytechnic Institute, Blacksburg, Va. 
24061. 
1 
