PLANOCERA INQUILINA, A POLYCLAD INHABIT-— 
ING THE BRANCHIAL CHAMBER OF SYCO- 
TYPUS CANALICULATUS, GILE, 
WILLIAM MORTON WHEELER. 
In glancing over a recent paper by Verrill’ on the marine 
planarians of New England—a work which the sea-side 
zoologist will find extremely useful—TI find no mention of a 
curious Polyclad, which is nevertheless quite common in Vine- 
yard Sound, Mass., the locality in which much of Verrill’s 
material was collected. Having likewise failed to find any 
mention of this species in the writings of Lang? and v. Graff,® 
I conclude that it is new. Perhaps the most interesting 
peculiarity of this new form, which undoubtedly belongs to the 
genus Planocera, as defined by Lang, is its parasitic mode of 
life. After reviewing all the cases of supposed parasitism 
among Polyclads, Lang concludes with the words (p. 630): 
«Kurz, es erscheint mehr als zweifelhaft, dass irgend eine der 
bis jetzt bekannten Polycladen wirklich eine parasitische 
Lebensweise fiihre.’ The new P/lanocera, however, seems to 
be a true ectoparasite, although I am not sure that it sucks 
the juices of the mollusk on which it lives.t In all I have 
opened about 100 adult specimens of Sycotypus, and in the 
branchial chamber of nearly every individual from one to six of 
1 A. E. Verrill, Marine Planarians of New England. Trans. Conn. Acad. Vol. 
VIII Jan. 1893. pp. 79-140, Pl. XL-XLIV. 
2 A. Lang, Die Polycladen. Fauna u. Flora des Golfes v. Neapel. XI Mono- 
graphie. Leipzig: Engelmann, 1884. pp. i-ix + 1-688. Taf. I-XXXIX. 
8. v. Graff, Pelagische Polycladen. Zeitsch. f. wiss. Zool. 55. Bd. 2. Heft. 
pp. 189-219. Taf. VII-X. 1892. aLG 
4 Possit*, 7, -ochus zebra, Verrill, may be somewhat parasitic. This beautifpl 
species is not uncommon at Wood’s Holl in the dead shells of Lunatia heros 
tenanted by hermit crabs and invested with Hydractinia. Whether the planarian 
merely selects the Zwma/ia shell as a hiding-place or bears some definite relation 
to the hermit crab, I am unable to decide. Verrill (/oc. c#z. p. 84) also mentions its 
occurrence in the “dead shells of Audgur that were occupied by hermit crabs, 
Eupagurus pollicaris.” 
