28: 



CRUSTACEANS. 



ACORN-BARNACLE (uat. size). 



Coronula, or coronet-barnacles, attach themselves to the skin of whales. The 



burrowing-barnacle (Tubicinella) has the same instinct. When adult it is long 



and cylindrical, 

 consisting of a 

 stout, stony rod, 

 marked with a 

 series of annular 

 ridges. This is 

 buried deeply in 

 the skin of whales, 

 sometimes pene- 

 trating as far as the blubber. 



These Cirripedes are not true par- 

 asites, inasmuch as they do not extract 

 nourishment from the animal to which 

 they are attached ; but many members 

 of the group live exclusively upon other 

 living beings, and nourish themselves at 

 their expense. One form, for instance, 

 Proteolepas, is in the 

 adult condition a 

 mag g o t - sh a p e d, 

 limbless, shell - less 

 body, living within 

 the mantle-chamber 



of other members of the same order ; while the root-headed Cirripedes (Rhizocephala) 



live parasitically upon the higher crustaceans. They 



are degenerate forms, possessing neither appendages 



nor segments, the body being; a mere sac, devoid of 



alimentary canal, and absorbing nutriment by means 



of the root-like processes branching throughout the 



body of the host. 



Bivalved Group, — Order Ostracoda. 



This order is a small assemblage, characterised by 



the possession of a bivalved shell, formed from the 



right and left halves of the carapace, and furnished 



with an elastic hinge to separate the valves and a 



muscle to keep them shut. The shell encloses the 



body which is unsegmented, has a rudimentary 



abdomen, and bears seven pairs of appendages, 



namely, two pairs of antennae, three pairs of jaws 



each belonging to the head, and two of limbs attached u PP er Fi s ure —Pdtogwt 



, , rrn ■,. t (enlarged H times) ; Lower 



to the thorax. Ihese limbs, however, are stout and Figure— JVauplius larva of Par- 



na rnnv. and, as a rule, there are no special respiratory thenopea (enlarged 200 times). 



STALKLESS BARNACLE (liat. Size 



fW 



PARASITIC CIRRIPEDE, 



Sacculina (nat. size). 



PARASITIC BAHNACLES. 



