Ellobiopsidae of Alaskan Coastal Waters- — -Hoffman and Yancey 
75 
usual frequency or that the parasite interferes 
with the regulation of molting. In the former 
case, the external development of T. fagei dur- 
ing the intermolt would of necessity be ex- 
tremely rapid. If the latter is true, as is the case 
with the rhizocephalans, molting would be held 
in abeyance while the external development and 
assumed reproduction of T. fagei take place. 
In order to resolve this question and others, 
work on the internal development needs to be 
undertaken. Most studies on ellobiopsids, Includ- 
ing this one, have dealt with the external aspects 
of these parasites only, while in reality it is the 
internal aspects which will reveal their biological 
status. 
The observations on the effect of Tbalas- 
somyces fagei on Tbysanoessa raschii agree with 
the reports of Einarsson (1945) on the effects 
of T. fagei on Tbysanoessa inermis. Einarsson 
stated that T. fagei probably castrates the animal 
it attacks. None of the parasitized Tbysanoessa 
raschii examined in this study had either the 
male antennal armature or the first pleopods de- 
veloped as copulatory organs; in the case of 
females no sign of a thelycum was evident. 
Einarsson (1945) showed that parasitized ma- 
ture females had completely disorganized ovaries 
through which ramifications of the stalk of the 
parasite extended. 
Boschma (1949) sectioned parasitized eu- 
phausids and found that the ellobiopsid did not 
disorganize the host’s ovary, although the pro- 
toplasmic excrescences which protrude through 
holes in the sieve plate extended throughout the 
organ. The ovary was not degenerated, although 
Boschma found that all the eggs present were 
small 
The most complete works on the genus Th al- 
as somyces are those by Boschma ( 1949 and 
1959), which contain a comprehensive review 
of the literature as well as descriptions of the 
species. 
On the basis of these and other observa- 
tions concerning the biology of ellobiopsids, 
a number of conclusions and hypotheses can 
be drawn concerning members of the genus 
Thalassomyces. 
1. The development of the structures external 
to the euphausid and the similarity of these to 
reproductive structures of Eliobiopsis strongly 
suggest that they are primarily reproductive. 
These external structures follow the establish- 
ment of a large internal body thought to be of 
a vegetative nature. The length of "life” of the 
internal portion of the parasite and its seasonal 
presence are unknown. Therefore the true per- 
centage infection cannot be determined on the 
basis of the external structures alone. 
2. The external reproductive structures of T. 
fagei appear In early summer in Alaska, whereas 
they appear in midsummer in the Atlantic. The 
duration of this manifestation of individual 
ellobiopsids Is unknown. 
3. Our observations in this study and those of 
Einarsson and Boschma on the sexual develop- 
ment of euphausids support the interpretation 
that T. fagei suppresses the sexual development 
of the host. Also the ellobiopsid may interfere 
with the endocrine control of molting, at least 
during its period of external development. 
4. Further understanding of the biological 
effects of these parasites on planktonic crusta- 
ceans will be achieved only by laboratory in- 
vestigations on the internal development of the 
parasite and on the nature and fate of the bodies 
produced in the gonomere. 
Th alas somyces sp. 
Six specimens of Thalassomyces sp. were 
found to parasitize the mysid Acanthomysis 
pseudomacropsis. The ellobiopsid is generally 
located on the dorsal surface of the carapace of 
the mysid. In each case the mysid was para- 
sitized by two ellobiopsids. In one instance, one 
of the ellobiopsids was located on the carapace, 
and the other was on the dorsal surface of the 
sixth abdominal segment of the mysid. The 
mature Thalassomyces specimens were taken in 
plankton samples from stations in the Kachemak 
Bay area of Alaska (59°27'N, 151°33'W) in 
October and December, 1963 and in February, 
1964. 
The mature parasite has 7-20 short-stalked 
trophomeres which are ramifications of the 
single central stalk. The trophomeres average 
0.75 mm long, although this feature is variable. 
The usual number of gonomeres present on each 
trophomere is three, and no more than this riurn- 
