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FISHERY BULLETIN: VOL. 73, NO. 1 



The mature distal gonomeres further subdivide 

 to produce motile biflagellate spores (Gait and 

 Whisler 1970). 



The internal portion of a parasitic ellobiopsid, 

 the organ of fixation, may be compact (like a 

 bulb or taproot — Figure 1) or may be branching 

 (rhizomorphous). The compact forms bear ridged 

 sieve plates from which extend fine protoplasmic 

 filaments. These filaments are believed to absorb 

 nutrients from the host. The internal portions 

 are difficult to observe without staining and sec- 

 tioning techniques and have not been used much 

 for taxonomic purposes. 



The nonparasitic epibionts of the genus Ello- 

 biocystis Coutiere do not have an internal organ 

 of fixation but attach directly to the host's cuticle. 

 These epibionts superficially resemble single 

 trophomeres of the parasitic ellobiopsids but 

 usually have a single gonomere. They are small 

 and attached singly or in clusters to the mouth 

 parts of various shrimps, mysids, and amphipods. 

 Only the morphology of the Ellobiocystis spp. 

 has been described. The inclusion of Ellobiocystis 

 spp. in the Ellobiopsidae is very questionable. 



Other than their morphology, little is known 

 about the ellobiopsids of the genus Thalassomyces 

 or their effects on hosts. The development of 

 reproductive spores has been described (Gait and 

 Whisler 1970); however, the mode of infection, 

 time required to mature, and true incidence of 

 infection remain subjects of speculation. Some 

 of the parasitic ellobiopsids sterilize the hosts 

 and probably exert some control on the molting 

 cycle of crustacean hosts. Undoubtedly, the 

 parasites draw heavily on the metabolic resources 

 of the hosts, which conceivably would increase 

 mortality and decrease reproduction in the host 

 populations. 



Ellobiopsids were first recognized as a compo- 

 nent of the northeastern Pacific fauna when Mc- 

 Cauley (1962) recorded Thalassomyces capillosus 

 (Page) as a parasite of the shrimp Pasiphaea 

 pacifica Rathbun. Since then eight additional 

 ellobiopsids have been recognized in zooplank- 

 ton collections from the eastern North Pacific. 

 Only two species of ellobiopsids have been re- 

 ported from the western North Pacific. In the fol- 

 lowing discussions for each species, I summarize 

 observations, some new and some from the litera- 

 ture, on the occurrence ^nd hosts of the North 

 Pacific ellobiopsids. I list synonymies only for 

 references to material from the North Pacific. 



For convenience only, I have treated those ello- 

 biopsids found on mysids first and those found 

 on amphipods, euphausiids, shrimp, and copepods 

 second. 



ARTIFICIAL KEY TO 

 ELLOBIOPSIDS FOUND ON MYSIDS 



The published keys to the ellobiopsids (Kane 

 1964; Collard 1966) do not give complete coverage 

 to the ellobiopsids found on mysids. Kane's key 

 is restricted to genera of ellobiopsids, and Collard's 

 key covers only 9 of the 11 known species of 

 Thalassomyces. Identification of the known 

 species of Ellobiocystis, and Ellobiopsis and most 

 Thalassomyces is possible by reference to the 

 summaries by Boschma (1949, 1957, 1959). The 

 following key supplements Collard's but treats 

 only the ellobiopsids found on mysids. Two of 

 the species, T. nouveli (Hoenigman 1954) and 

 T. niezabitowskii (Hoenigman 1960), are known 

 only from the Mediterranean Sea; and Ellobio- 

 cystis caridarum (Coutiere) while not known 

 from North Pacific mysids is found on Antarctic 

 mysids (Boschma 1949, 1959) and has been found 

 on the North Pacific decapod shrimp Pasiphaea 

 pacifica. 



1. No root system of attachment to host; 



attached to oral appendages. Mature 

 parasite consists of single trophomere 



with one or more gonomeres 



Ellobiocystis caridarum. (Coutiere) 



Root system of attachment to host; not 

 attached to oral appendages. Mature 

 parasite with many trophomeres 

 branching from stalk(s) . .Thalassomyces (2) 



2. Parasite attached to ventral surface of 



first abdominal segment. Long pendu- 

 lous umbellate trophomeres; usually 

 only one gonomere per trophomere 

 (length of ma.ture gonomere 1.5 to over 

 2 times the diameter) . . .T. fasciatus (Fage) 

 Site of attachment usually dorsal thoracic, 

 but variable. Trophomeres not pendu- 

 lous; usually more than one gonomere 

 per trophomere (2-4) (3) 



3. Mature gonomeres flattened spheres. 



Mean length-diameter ratio less than 1 



T. nouveli (Hoenigman) 



Mature gonomeres globular to oval. Mean 

 length-diameter ratio greater than 1 . . . .(4) 



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