76 
PACIFIC SCIENCE, Vol. XX, January 1966 
ber have been observed. The transverse diameter 
of the gonomeres ranges from 0.14 to 0.21 mm, 
the average being 0.17 mm. 
The species identification of these specimens 
has not been determined. This ellobiopsid may 
be T. fagei, although there are differences in a 
number of external features of Thalassomyces 
sp. from the specimens of T. fagei parasitic on 
the euphausid Thysanoessa raschii taken in the 
same area. The number of trophomeres, the 
length of the trophomere stalk, and the number 
of gonomeres vary from the previously men- 
tioned species. Boschma (1959) pointed out 
that a number of variations of this type occur 
among T. fagei individuals parasitic on different 
species of euphausids. The location of the ello- 
biopsid on the carapace tends to support the 
hypothesis that this is T. fagei, while the fact 
that this species parasitizes a mysid rather than 
a euphausid may be sufficient to propose this as 
a new species, inasmuch as T. fagei has only 
euphausid hosts. The only Thalassomyces species 
repotted to parasitize a mysid is T. fasciatus. 
This ellobiopsid is located on the ventral side of 
the first abdominal segment of its host. 
Until more material is available and can be 
examined by an authority, it is advisable to con- 
sider this ellobiopsid as Thalassomyces sp. 
Thalassomyces capillosus 
The first report of ellobiopsids from the 
northern and eastern Pacific was that of Mc- 
Cauley (1962). He found Thalassomyces capil- 
losus (Fage), formerly known as Amallocystis 
capillosus, on a specimen of Pasiphaea pacifica 
Rathbun, a pelagic shrimp taken 15 miles west 
of Coos Bay, Oregon (43°20.4'N, 124°45.8' W) 
in a mid water trawl. McCauley ( 1962 ) stated, 
"This work adds P. pacifica as a host and extends 
the known range of this parasite to the north- 
eastern Pacific.” According to McCauley, T. 
capillosus had previously been described as para- 
sitic on several species of pasiphaeid shrimp, 
most of which were taken in the north Atlantic. 
Five Pasiphaea pacifica taken by the Explora- 
tory Fishing and Gear Research Base of the 
Bureau of Commercial Fisheries, Juneau, Alaska, 
were examined for ellobiopsids. A single speci- 
men of P. pacifica taken by a shrimp trawl at 
station No. 427 located in Orca Bay, Prince Wil- 
liam Sound, Alaska (60°34'N, 146°01'W) was 
parasitized. This individual was taken between 
depths of 74 and 120 fathoms on September 9, 
1962, by Rathjen (1963). In addition, a single 
specimen taken in Lynn Canal in southeastern 
Alaska ( 58°51.2' N, 135°15.5'W) was para- 
sitized by T. capillosus. This pasiphaeid was 
taken May 14, 1964, by an Isaac-Kidd midwater 
trawl at a depth of 59.6 fathoms. 
The ellobiopsid is located dorsal to the eyes of 
the host at the base of the rostrum. On one speci- 
men there were approximately 40-50 tropho- 
meres on either side of the rostrum; on the other 
specimen there were 50-60. This estimation of 
the number of trophomeres on the first may not 
be accurate because the specimen was in poor 
condition. Distal to the trophomere of the para- 
site is one or, more commonly, two gonomeres. 
The terminal gonomere is ovoid, almost twice as 
long as broad. When two gonomeres are present, 
the proximal one is somewhat rectangular be- 
cause of the septa which separate it from the 
more distal gonomere and from the trophomere. 
The morphology of the parasite, its size and 
location on the host, and the host species agree 
for the most part with the description of T. cap- 
illosus (Fage). The only discrepancy was that 
rather than a single gonomere there were almost 
always two gonomeres on each trophomere. 
Effects of T. capillosus on the carapace of 
P. pacifica similar to those found by McCauley 
were noted. The rostrum is distorted and projects 
almost dorsad rather than anteriad. On either 
side of the base of the rostrum is a swelling not 
found in unparasitized P. pacifica. A dumbbell- 
shaped opening in the carapace extends between 
the two swellings. A tuft of trophomeres of 
T. capillosus extends from the tissue of the host 
through both of the expanded ends of the slit. 
Figure 5 is a camera lucida drawing illustrating 
the rostrum of a parasitized P. pacifica. 
This study extends the known range of T. 
capillosus as a parasite on Pasiphaea pacifica 
from off the Oregon coast (McCauley, 1962) to 
the Prince William Sound area of Alaska. It is 
expected that further observations will fill in 
the range and possibly extend it still farther. 
