Ji 



THE OTTAWA NATURALIST 



Vol. XXVI. JANUARY, 1913 No. 10 



A NEW CANADIAN CIRRIPEDE, PARASITIC ON A 



SHRIMP. 



(Resume of Mr. F. A. Potts' research at B. C. Biological Station). 



By Professor E. E. Prince, Commissioner of Fisheries, 



Ottawa. - 



The naturalist who spends hours on the sea- shore, now and 

 then finds specimens of shore crabs, on the under-side of which 

 is attached a yellowish brown mass, resembling a small potato. 

 This soft rounded lump is really the mature stage of a parasitic 

 crustacean. Just as a pug and a greyhound show dissimilarities, 

 though a child knows that both are dogs, so this sac-like parasite 

 is a crustacean, a member of the Order Cirripedia or Barnacles, 

 which Order, Dr. Starr Jordan says, furnishes an example of 

 "degeneration through quiescence . . . the barnacles being 

 most nearly related to the crabs and shrimps." Charles Darwin 

 gained early fame by his studies of the Cirripedes, and his mono- 

 graph on the Order is a classic of zoological science. In early 

 life each passes through one or more active stages, and later 

 becomes fixed and wondrously transformed. The transforma- 

 tion is one of degeneration, but while the barnacle (Fam. 

 Balanidas) is strange enough in its changes, the sub-order 

 Rhizocephala furnish us with the most extraordinary examples. 

 The sac-like parasite referred to above is rightly called Sacculina. 

 It comes from the egg as a minute water-flea called a Nauplius, 

 and changes into the more complex Metanauplius, and after 

 swimming about freely it attaches itself to a crab, penetrates 

 the crab's shell with one of its hollow antennae. Now 

 follows one of the most marvellous circumstances in the entire 

 range of biology. The whole of the soft contents of the Cirripede's 

 body is squeezed through the hollow tube or antenna into the 

 body of the crab, rather recalling a cat squeezing its way through 

 a small drain pipe. Soon it works its way to the intestine of 

 the host, but later pushes to the exterior, hanging on as a sac, 

 below the crab by a short peduncle. The top of this neck 

 shows branching roots, which penetrate the organs of the crab, 



