This paper presents preliminary data on the population structure of two Antarctic crustaceans Eudorella splendida and Nototanais antarcticus, commonly occurring in Admiralty Bay (South Shetland Islands). From analysis of the material studied it can be concluded that N. antarcticus is a progynous hermaphrodite with a life cycle lasting at least two years. The life cycle of E. splendida lasts probably 3-4 years. It is a semelparous species, but some females after brooding moult and revert into the intermediate stage.

Cumacean crustaceans found in 188 qualitative and quantitative samples of zoobenthos collected in Admiralty Bay (King George Island, South Shetlands) by successive Polish Antarctic Expeditions in the years 1977 — 1989 were studied. In over 3000 individuals of these crustaceans 12 taxa were recognized. Eudorella splendida clearly dominated the material. Other common species were Campylaspis maculata and Vaunthompsonia inermis. The highest cumacean density amounted to 2618 ind.m-2 . Clear differences were observed between cumacean faunas of small grain sediment (muddy Ezcurra Inlet) and of mixed, coarser sediments (central part of Admiralty Bay with sand, gravel and mud). The dominance of Eudorella splendida was strongly marked in shallow Ezcurra Inlet whereas in deeper central part of Admiralty Bay the cumacean fauna was much more diversifield.

Eleven species of cumaceans were found in 105 samples collected in Admiralty Bay (King George Island) in the summers of 1984/85 and 1985/86, from 20 to 500 m depth range. Four cumacean assemblages were distinguished using the multivariate analysis. They were characterized by the dominance of one or two species often with low density values. Two assemblages were found in open waters of Admiralty Bay. The first inhabited on sandy−clay−silt and silty−clay−sand bottom deposits in the depth range from 140 to 330 m, with Campylaspis maculata (1.6 ± 2.1 ind./0.1m 2 ; F = 72.4%) and Leucon sp. (1.4 ± 1.6 ind./0.1m 2 ; F = 68.9%) as key species. The second assemblage was found in the depth range from 50 to 120 m with silty−sand sediments, and it was characterized by the presence of Vauthompsonia inermis (6.5 ± 6.6 ind./0.1m 2 ; F = 92.0%). A third assemblage was found in shallow waters influenced by glaciers in the bottom area of Ezcurra Inlet. It was characterized by sandy−clay−silt sediments and the presence of Eudorella splendida (14.6 ± 9.4 ind./0.1m 2 ; F = 100.0%) as a core species. The last assemblage was found in the shallow sublittoral (50–100 m) of Ezcurra Inlet and the central basin, with Diastylis anderssoni armata (1.5 ± 1.1 ind./0.1m 2 ; F = 85.7%) and Diastylopsis goekei (1.1 ± 1.0 ind./0.1m 2 ; F = 71.4%) as the most frequent and abundant species. V. inermis is considered a eurytopic species with high frequency in the whole material, and was present in all four distinguished assemblages. E. splendida and D. goekei were also recorded in each of the assemblages, but their total frequency was lower.