A PARASITIC OR COMMENSAL OLIGOCHA:TE 
IN NEW ENGLAND. 
M. A. WILLCOX. 
Chetogaster limnei von Baer appears to be the only oligo- 
chæte which is generally recognized as a parasite ; at least it 
is the only one to which Michaelsen in his recent work on the 
subclass (Das Tierreich, Oligocheta, 1900) ascribes such habits. 
The species has been reported only from Europe, and it is there- 
fore with pleasure that I am able to announce the discovery in 
the neighborhood of Boston of a very similar form, regarding 
which I can at present give only the following incomplete notes. 
The worms were first found about the end of May, 1901, 
infesting a species of Physa, probably P. heterostropha, which 
was obtained in a small stream in Wellesley. They were also 
afterward observed upon an undetermined species of Planorbis. 
They were abundant about the head and in the respiratory cav- 
ity. Ina few instances the hinder part of the body seemed to 
be imbedded in the tissues of the snail, but of this I cannot be 
Sure. Most of them certainly were entirely free, and, waving 
about like tiny white threads, had much the appearance of a 
fungus, Occasionally I have noticed them, like the European 
form, crawling over the outside of the shell ; but they ordinarily 
restrict themselves to the body of the snail. 
This is undoubtedly the animal mentioned by Gould (Report 
on the Invertebrate Animals of Massachusetts, 1841, P. 213) 
under the name of Gordius inguilinus Müller, and supposed 
by him to be a parasite of P. heterostropha. In none of 
specimens taken under ordinary conditions, boweven n s 
alimentary tract give any indications of a parasitic ha idit 
the contrary, I have seen in it no other food tha n : 
It will be remembered that Lankester in his €— : 
the European form («A Contribution to the €: e VI 
the Lower Annelids,” Trans. Linn. Soc., Lond., Vol. $ 
905 
n diatoms. 
