12. PREDATORS AND PARASITES
369
originates from the parasites. Little is known about the parasites of
euphausiids, information only being available for the “ macroparasites ” such as Thalassomyces fagei (Boschma), an ellobiopsid, and
a crustacean, Branchiophryxus nyctiphanae (Caullery). No information
on worms or Protozoa that parasitize euphausiids is available.
The crustacean bopyrid, B. nyctiphanae, was described by Caullery
(1897) from specimens of Meganyctiphanes norvegica and again by Masi
(1905). The parasite was attached by the anterior part of its ventral
surface to the last gill of the host. No other records of this organism
parasitizing an euphausiid are known. There is, however, considerable
information on the ellobiopsid parasite. This parasite has been found
on thirteen species of euphausiids (Mauchline, 196613). These species are
Meganyctiphanes norvegica, Nyctiphanes australis, Euphausia frigida,
E. hemigibba, E. krohnii, E. lucens, E . pseudogibba, E. recurva, E.
vallentini, Thysanoessa raschii, T . inermis, T . gregaria, and Nematoscelis
dificilis. The parasite is normally found protruding from the median
dorsal surface of the carapace but is occasionally found attached t o the
basal segment of one of the posterior pair of limbs. Its development in
Thysanoessa raschii has been studied by Hoffman and Yancey (1966)
and Mauchline (1966b). It is first noticeable as a small body present in
the region of the gonads under the carapace (Fig. 130, A). This grows
in size and a finger-like extension penetrates the carapace while a
‘ I root ” grows downward into the gonadal tissues. The end of the
dorsal process begins to differentiate in a dichotomous manner (Fig.
130, C and D) to form the developing trophomeres which themselves
are finger-like in form. The trophomores are not segmented a t the stage
illustrated in Fig. 130, E where they have attained a length of 0.2 to
0.25 mm. The segments, or gonomeres, form in trophomeres of length
0.6-0.75 mm and it is a t this stage that the “ root ” develops more
intimate connexions with the host’s tissues and it is no longer possible
to dissect the entire parasite from the host. About 10% of parasitized
Thysanoessa raschii were infected with a Thalassomyces fagei whose
root had produced two or more sets of trophomeres (Fig. 131, B, C, D).
In all, 330 parasitized Thysanoessa raschii were examined and no
euphausiid was found to be infected by more than a single Thalassomyces
fagei. Further, the parasite was not found invariably to prevent the
development of secondary sexual characteristics as had been earlier
reported by other authors; in fact, these were well developed in 224 of
the 330 infected Thysanoessa raschii and some 15-20% of the infected
males were found with spermatophores present in their ejaculatory
ducts. It is, however, probable that these spermatophores were formed
prior to the testicular vesicles being invaded by the root of the parasite
369
originates from the parasites. Little is known about the parasites of
euphausiids, information only being available for the “ macroparasites ” such as Thalassomyces fagei (Boschma), an ellobiopsid, and
a crustacean, Branchiophryxus nyctiphanae (Caullery). No information
on worms or Protozoa that parasitize euphausiids is available.
The crustacean bopyrid, B. nyctiphanae, was described by Caullery
(1897) from specimens of Meganyctiphanes norvegica and again by Masi
(1905). The parasite was attached by the anterior part of its ventral
surface to the last gill of the host. No other records of this organism
parasitizing an euphausiid are known. There is, however, considerable
information on the ellobiopsid parasite. This parasite has been found
on thirteen species of euphausiids (Mauchline, 196613). These species are
Meganyctiphanes norvegica, Nyctiphanes australis, Euphausia frigida,
E. hemigibba, E. krohnii, E. lucens, E . pseudogibba, E. recurva, E.
vallentini, Thysanoessa raschii, T . inermis, T . gregaria, and Nematoscelis
dificilis. The parasite is normally found protruding from the median
dorsal surface of the carapace but is occasionally found attached t o the
basal segment of one of the posterior pair of limbs. Its development in
Thysanoessa raschii has been studied by Hoffman and Yancey (1966)
and Mauchline (1966b). It is first noticeable as a small body present in
the region of the gonads under the carapace (Fig. 130, A). This grows
in size and a finger-like extension penetrates the carapace while a
‘ I root ” grows downward into the gonadal tissues. The end of the
dorsal process begins to differentiate in a dichotomous manner (Fig.
130, C and D) to form the developing trophomeres which themselves
are finger-like in form. The trophomores are not segmented a t the stage
illustrated in Fig. 130, E where they have attained a length of 0.2 to
0.25 mm. The segments, or gonomeres, form in trophomeres of length
0.6-0.75 mm and it is a t this stage that the “ root ” develops more
intimate connexions with the host’s tissues and it is no longer possible
to dissect the entire parasite from the host. About 10% of parasitized
Thysanoessa raschii were infected with a Thalassomyces fagei whose
root had produced two or more sets of trophomeres (Fig. 131, B, C, D).
In all, 330 parasitized Thysanoessa raschii were examined and no
euphausiid was found to be infected by more than a single Thalassomyces
fagei. Further, the parasite was not found invariably to prevent the
development of secondary sexual characteristics as had been earlier
reported by other authors; in fact, these were well developed in 224 of
the 330 infected Thysanoessa raschii and some 15-20% of the infected
males were found with spermatophores present in their ejaculatory
ducts. It is, however, probable that these spermatophores were formed
prior to the testicular vesicles being invaded by the root of the parasite