28 
CRUSTACEANS. 
acorn-barnacle (nat. size). 
Coronula, or coronet-barnacles, attach themselves to the skin of whales. The 
burrow ing-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 
maggot - 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. 
STALKLESS BARNACLE (nat. Size). 
PARASITIC CIRRIPEDE, 
Sacculina (nat. size). 
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 antennay three pairs of jaws 
each belonging to the head, and two of limbs attached 
to the thorax. These limbs, however, are stout and 
narrow, and, as a rule, there are no special respiratory 
PARASITIC BARNACLES. 
Upper Figure —Peltogaster curvatus 
(enlarged 1^ times) ; Lower 
Figure — Wa uplius larva of Par- 
thenopea (enlarged 200 times). 
