104 specimens of notothenioid fishes of five species (Patagonotothen longipes, P. tessellata, Champsocephalus esox, Cottoperca trigloides and Patagonotothen brevicauda) caught at two sites in the Beagle Channel (Magellanic sub-region, sub-Antarctica) were examined for the presence of thorny-headed worms (Acanthocephala). Representatives of three fish species, Patagonotothen longipes, P. tessellata, and Champsocephalus esox, were infected. Fishes caught at the eastern mouth of the channel were infected with 180 echinorhynchids representing three species, Aspersentis johni (the most numerous species), Heterosentis heteracanthus, and Hypoechinorhynchus magellanicus, and only 12 cystacanths of four polymorphids, Andracantha baylisi, Corynosoma sp., Corynosoma beaglense, and Corynosoma evae. Patagonotothen longipes was the most highly infected in the eastern mouth of the channel (prevalence 85%, maximum intensity 26). Aspersentis johni was the dominant parasite species in this host (prevalence 85%, mean abundance 4.00, maximum intensity 18) and H. heteracanthus was the sub-dominant one (prevalence 50%, mean abundance 2.60, maximum intensity 25). The infections of C. esox were the most diverse (six parasite species - three echinorhynchids and three polymorphids). Fish caught near the city of Ushuaia were infected only with six cystacanths of C. evae (intensity one). Taking into account the whole sample, C. evae was the most abundant polymorphid, represented by 10 of 18 specimens found. Three species, H. heteracanthus, A. baylisi and C. evae, have been previously reported from the low western Antarctic (H. heteracanthus also from the Kerguelen sub-region of sub-Antarctic), remaining four species seem to be endemics of the Magellanic sub-region of sub-Antarctic.

In total, 8511 amphipods of 12 species caught in Admiralty Bay were examined for the presence of acanthocephalans using them as intermediate hosts. Only 27 specimens of eight species were infected (total prevalence 0.32%). Acanthellae and cystacanths of four species using fishes as either definitive or paratenic hosts were found. Normally, single parasites occurred; in one case two acanthocephalans were present in one specimen of Bovallia gigantea. This host species was the most strongly infected, with the prevalence 3.41%. Six other amphipod species were infected with the prevalence 0.08-0.66%. One of two Jassa ingens examined was also infected. Over 50% of acanthocephalans belonged to one echinorhynchid species maturing in fishes, Aspersentis megarhynchus, which occurred in five host species of four amphipod families, B. gigantea, Gondogeneia antarctica, J. ingens, Hippomedon kergueleni and Orchomenella rotundi-frons. Two polymorphid species maturing in seals, Corynosoma hamanni and C. pseudohamanni, were found in a single host species each, Prostebbingia brevicornis and Cheirimedon femoratus, respectively. Three parasite species mentioned occurred exclusively in sublittoral host species, at the depth 0-30 m. The third polymorphid species, C. bullosum, was the only species occurring in the amphipod, Waldeckia obesa, living in the deeper water (infected specimen was caught at the depth 60 m), but was found also in B. gigantea. Differences between infections of Amphipoda and fishes with echinorhynchids and polymorphids are discussed.

The paper comprises the review of all 23 known valid species along with synonyms and polytomic keys based on morphological features. Mature specimens of 8 species occur in fishes, 4 in birds, 11 in mammals. Each species settles in a definite section of the digestive tract. The structure of a population is dependent upon the time which has passed since the moment of invasion and the intensity of infestation. Acathocephalans can be found in hosts all the year round, but incomplete seasonality of the occurrence of 2 fish parasites has been recorded. Fish parasites show wide specificity in relation to the hosts mentioned while bird and mammal parasites specificity is narrow. The majority of acanthocephalan species have circumpolar distribution but only 3 have been found inside the polar circle and the other 7 are common in the environs of subcontinental archipelagoes. Acanthocephalans do not yield precedence as far as the diversity of species and infestation intensity are concerned in the Antarctic to other groups of parasite helminths. Their great importance results from their mass occurrence in the vertebrates which are the focus of. man's practical interests — fishes, seals and whales.

In total, 18 species and larval forms of endoparasitic worms were found in 19 newly examined notothenioid fishes of three species, Trematomus hansom, Notothenia coriiceps and Chionodraco hamatus, caught off Adelie Land. One digenean species, Neolepidapedon trema-tomi, was recorded in this area for the first time. A total list of endoparasitic worms prepared by Zdzitowiecki etal. (1998) increased from 20 to 21 species and larval forms and concerns 11 deter­mined and one determined species of Digenea (the most diverse group), three larval forms of Cestoda, three species (one identified only to genus) of Acanthocephala, two species (one in the larval stage) and one larval form of Nematoda. All these species and forms, with the exception of the indetcrmined digenean, occur also in the deep Antarctica, in the Ross Sea and/or in the Weddell Sea. The prevalence and relative density of infection with each parasite in three host species is given based on summarized previous and new data.

Adult females of a predatory fish, the blackfin icefish, Chaenocephalus aceratus examined at the South Shetland Islands and South Orkney Islands were by several orders of magnitude more infected with Acanthocephala than the males and immature females. Such phenomenon has not been observed in the neritic zone at South Georgia. Cystacanths of Corynosoma hamanni and Corynosoma pseudohamanni were the dominant parasites in Admiralty Bay, whereas Corynosoma bullosum was the dominant in the open sea off the South Shetland Islands and South Georgia, and in the sub-coastal waters off the South Orkney Islands. However, the dominance of C. bullosum was observed in several hosts in Admiralty Bay and the co-dominance of C. bullosum, C. hamanni, and C. pseudohamanni in one mature female in the neritic zone at the South Shetland Islands. Probably, these fish previously lived in the open sea. Cystacanths of Corynosoma arctocephali and Corynosoma shackletoni occurred in the fish in Admiralty Bay and off South Georgia. The former parasite was present also off the South Orkney Islands. One cystacanth of Andracantha baylisi was found off South Georgia. Two echinorhynchids, Aspersentis megarhynchus and Metacanthocephalus dalmori, occurred in the alimentary tracts of the fish caught in Admiralty Bay and one specimen of Echinorhynchus petrotschenkoi off the South Shetland Islands. The highest infection, amounting to 816 acanthocephalans, was found in a mature female in Admiralty Bay. One cystacanth of C. hamanni occurred in a single immature fish caught in the sub-coastal area off Deception Island.

A comparison between the levels of infection with Acanthocephala of the fish Notothenia coriiceps in Admiralty Bay (South Shetland Islands, Antarctic) in 1978/79 and 2007/08 is presented. The same eight acanthocephalan species, three echinorhynchids maturing in fish, Aspersentis megarhynchus (dominant species), Metacanthocephalus johnstoni (subdominant species) and M. dalmori (common species), and five polymorphids maturing in mammals and birds, Corynosoma hamanni , C. pseudohamanni (both co−dominant species), C. arctocephali and C. bullosum (both common species), and C. shackletoni (rare species), were found. Echinorhynchids were more numerous in 2007/08 (mean abundance 46.54 versus 35.35 in 1978/79), whereas polymorphids more numerous in 1978/79 (mean abundance 74.35 versus 36.40 in 2007/08). The overall results therefore demonstrated that echinorhynchids were more numerous than polymorphids in 2007/08 and the reverse was true in 1978/79. This situation is dependent mainly upon the decreased infections with C. hamanni , C. pseudohamanni and C. bullosum , and to a lesser degree upon the increasing of infections with M. johnstoni . The decrease of the three Corynosoma spp. is possibly associated with the decreasing of populations of final hosts, seals, on the shore of Admiralty Bay in the vicinity of Arctowski Station.