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PACIFIC SCIENCE, Yol. XX, January 1966 
Fig. 1. A young ellobiopsid located in a concavity on the dorsal side of host’s carapace. 
off, leaving a small tuft, or the walls may col- 
lapse, producing a filament hanging from the 
end of a more proximal gonomere (Fig. 4/). 
Jepps (1937) has observed that in Ellobiopsis 
chattoni, parasitic on Calanus finmarchicus, this 
condition of the gonomere is the result of 
sporulation. She noted that when all the spores 
have been released, the test of the distal segment 
either degenerates or is left full of debris. 
The development of Thalassomyces fagei was 
worked out from a sequence of specimens taken 
in various stages of growth (Fig. 4). The ello- 
biopsid was removed from its host and placed 
with the stalk extending upward to facilitate 
drawing. The illustrations show this aspect of 
the parasite, except Figures Aa and Ab, which are 
views from one side. All the drawings were done 
with the aid of a camera lucida. 
It is not known whether the initial infection 
by the parasite is located internally or externally. 
Jepps (1937) hypothesized that E. chattoni 
initially penetrates the host from the outside. In 
the material of Thysanoessa raschii examined in 
the present study, Thalassomyces fagei was 
found to have a well-established internal struc- 
ture at the earliest stages in its external develop- 
ment. Figure Ab is a lateral view of T. fagei 
shown extending through the host carapace. The 
structure in the lower left is the "sieve plate” of 
Boschma (1949). Numerous protoplasmic ex- 
crescences protrude through openings in the 
cuticle of the ellobiopsid. These excrescences are 
thought to be the organ of absorption of food 
for the parasite. 
The major function of the external structure 
of the parasite is assumed to be reproductive. 
FIG. 2. Euphausid with two discrete parasites. 
