Diversity of Digenea, Parasites of Fishes in Various Areas of the Antarctic
89
digenean species in the W orId Ocean, is replaced in the high Antarctic by
Derogenes johnstoni. These species are closely related, but are
distinguishable on the base of dimensions and morphology of the egg
shell. The second pair of closely related species are Lecithaster
macrocotyle and L. micropsi. Their distribution is restricted to the southern
hemisphere. The former occurs in the low Antarctic, in the SubAntarctic
and rarely in the Ross Sea; the latter occurs in the SubAntarctic and off
South Georgia. Specimens of bo~h pairs of parasites occur partly in the
same fish species, for example Derogenes spp. in Trematomus hansoni,
and Lecithaster spp. in Chaenocephalus aceratus. It indicates that their
presence or absence is not associated with the distribution of final hosts,
but rather with the presence or absence of the particular molluscan hosts of
the parthenogenetic generations.
All other digenean species recorded in Antarctic fishes are intestinal
parasites. Fourteen species of the family Opecoelidae, accompanied by one
species endemic to the Kerguelen subregion, are listed in Table 2. Eight
species occur in the Eastern Antarctic, but only two of them also off the
South Shetland Islands. Two other species occur off South Georgia and in
the SubAntarctic. The specificity to final hosts is narrower than that of
Hemiuroidea. Eight species occur mainly or entirely in Notothenioidei,
three appear to be specific to the Muraenolepididae (two of them were
found in Nototheniidae, but all parasites were immature), one species is
specific to Zoarcidae, three species normally occur in both Nototheniidae
and either Zoarcidae or Congiopodidae. It should be noted, that three
species of parasites normally occurring in Notothenioidei rarely occur in
Liparididae and another one in Zoarcidae. Probably, we are observing the
moment of acquisition of new hosts and new species may be formed in
future. Some closely related but distinct species occur in different areas.
For example, Macvicaria pennelli occurs in the Ross Sea and South of the
Indian Ocean, M. georgiana - off the South Shetland Islands and South
Georgia, M. antarctica - in the SubAntarctic and rarely off South Georgia.
Similar digeneans occurring in the Weddell Sea appear to be
morphologically intermediate between typical M pennelli and M.
georgiana. They are tentatively assigned to the latter species. Similarly,
Neolebouria antarctica occurs in the Western Antarctic, whereas N
terranovaensis occurs in the Eastern Antarctic. Stenakron glacialis was
recorded in the subcontinental waters of the Antarctic, whereas S.
kerguelense was found in the Kerguelen subregion of the SubAntarctic. In
contrast, two representatives of the genus Discoverytrema occur in the
same host species (Muraenolepis microps), habitat (posterior part of the
small intestine) and locality (off South Georgia). The same is true for
Macvicaria georgiana and M microtestis in the Weddell Sea. No one
opecoelid species occurring in subcontinental waters was recorded in the
89
digenean species in the W orId Ocean, is replaced in the high Antarctic by
Derogenes johnstoni. These species are closely related, but are
distinguishable on the base of dimensions and morphology of the egg
shell. The second pair of closely related species are Lecithaster
macrocotyle and L. micropsi. Their distribution is restricted to the southern
hemisphere. The former occurs in the low Antarctic, in the SubAntarctic
and rarely in the Ross Sea; the latter occurs in the SubAntarctic and off
South Georgia. Specimens of bo~h pairs of parasites occur partly in the
same fish species, for example Derogenes spp. in Trematomus hansoni,
and Lecithaster spp. in Chaenocephalus aceratus. It indicates that their
presence or absence is not associated with the distribution of final hosts,
but rather with the presence or absence of the particular molluscan hosts of
the parthenogenetic generations.
All other digenean species recorded in Antarctic fishes are intestinal
parasites. Fourteen species of the family Opecoelidae, accompanied by one
species endemic to the Kerguelen subregion, are listed in Table 2. Eight
species occur in the Eastern Antarctic, but only two of them also off the
South Shetland Islands. Two other species occur off South Georgia and in
the SubAntarctic. The specificity to final hosts is narrower than that of
Hemiuroidea. Eight species occur mainly or entirely in Notothenioidei,
three appear to be specific to the Muraenolepididae (two of them were
found in Nototheniidae, but all parasites were immature), one species is
specific to Zoarcidae, three species normally occur in both Nototheniidae
and either Zoarcidae or Congiopodidae. It should be noted, that three
species of parasites normally occurring in Notothenioidei rarely occur in
Liparididae and another one in Zoarcidae. Probably, we are observing the
moment of acquisition of new hosts and new species may be formed in
future. Some closely related but distinct species occur in different areas.
For example, Macvicaria pennelli occurs in the Ross Sea and South of the
Indian Ocean, M. georgiana - off the South Shetland Islands and South
Georgia, M. antarctica - in the SubAntarctic and rarely off South Georgia.
Similar digeneans occurring in the Weddell Sea appear to be
morphologically intermediate between typical M pennelli and M.
georgiana. They are tentatively assigned to the latter species. Similarly,
Neolebouria antarctica occurs in the Western Antarctic, whereas N
terranovaensis occurs in the Eastern Antarctic. Stenakron glacialis was
recorded in the subcontinental waters of the Antarctic, whereas S.
kerguelense was found in the Kerguelen subregion of the SubAntarctic. In
contrast, two representatives of the genus Discoverytrema occur in the
same host species (Muraenolepis microps), habitat (posterior part of the
small intestine) and locality (off South Georgia). The same is true for
Macvicaria georgiana and M microtestis in the Weddell Sea. No one
opecoelid species occurring in subcontinental waters was recorded in the