Section IV, 1917 [47] Trans. R.S.C. 



Notes on some Crustacean forms occurring in the Plankton of 

 Passamaquoddy Bay. 



By J. Playfair McMurrich, M.A., Ph.D., LL.D., F.R.S.C. 



(Read May Meeting, 1917). 



In carrying out a qualitative study of the Plankton of Passama- 

 quoddy Bay with the object of determining its seasonal variations a 

 number of interesting forms were observed, some altogether new and 

 others hitherto unrecorded from the Eastern Atlantic. A record of 

 certain of these forms seemed desirable, even although the informa- 

 tion concerning them was by no means complete, and the present 

 paper is an account of certain adult and larval Crustacea, all of which 

 present features of interest. 



I. MONSTRILLA CANADENSIS N. SP. 



A single male example of the Copepodan family Monstrillidae 

 was taken on February 5th, 1916. This family is characterized by 

 the fact that the forms belonging to it lack all the appendages that 

 normally intervene between the first antennae and the first thoracic 

 limbs, and the mouth is reduced to a small circular opening, situated 

 upon a slight conical projection and opening into a pharynx, all other 

 portions of the digestive tract being absent. Such conditions point 

 to a parasitic life in the early stages and this has been demonstrated by 

 Malaquin.^ for one of the three genera, Haemocera, represented 

 in the family, the hosts proving to be Annelids, while by the same 

 author a similar association has also been indicated for Thaumaleus 

 germanicus. 



Of the genus Monstrilla the early stages have not yet been ob- 

 served, but a number of adults have been described, captured as free- 

 swimming plankton organisms. Taken as a rule only in small num- 

 bers, a single individual has, of necessity, in many instances formed the 

 basis for a specific description. Unfortunately the earlier descrip- 

 tions were not always as detailed as could be desired, and difficulties 

 have thereby been introduced into the synonomies of the species, 

 difficulties that have been increased by the facts that considerable 

 sexual dimorphism occurs in the group and that females are captured 

 somewhat more frequently than males. 



^A. Malaouin. Le parasitisme évolutif des Monstrillides. Arch, de zool. 



exp. et gen. Ser. 3. IX, 1901. 



