First finding of brittle star Ophiocnemis marmorata in jellyfishes of genus Rhopilema in waters of Vietnam is described.      Symbiosis between scyphomedusae and epizoic invertebrates, in particular with hyperiid amphipods, has long been known (Thiel 1976). However, the association of echinoderms with jellyfish is unusual and has seldom been reported.      Russian investigators worked in the Nhatrang Bay near the Tam Island in 2011. Underwater they could meet enough greater number Scyphozoa jellyfishes Rhopilema hispidum (Vanhöffen, 1888).      Inside of a bell of many jellyfishes were visible brittle stars. One such jellyfish was placed in a bucket under water and delivered aboard a vessel together with all symbionts. Among symbionts there were 9 juvenile fishes, 7 swimming crabs Charybdis feriata (Linnaeus, 1758), 4 shrimps and 5 brittle star specimens Ophiocnemis marmorata (Lamarck, 1816).

A new species of Eleutherobia is described, enlarging the Eleutherobia species group that lack sclerites in the anthocodiae. The Octocorallia of the South-China Sea are poorly known, and the data that is presented provides a new record of the genus for Vietnam. The original description of Sinularia manaarensis Verseveldt, 1980 was based on a single incomplete colony fragment collected in 1902 near Ceylon (Verseveldt, 1980, Pl. 16, Fig. 3). Here we present data on both living and preserved S. manaarensis colonies that were found in Nha Trang Bay (South China Sea) in 2006. The club-shaped surface sclerites with wide flattened handles are characteristic of the species. Images of live colonies are given along with a biogeographical discussion. S. arctium sp. nov., is also described. It has a remarkable assortment of sclerites, which includes both leptoclados- like clubs and warty clubs with a distinct central wart.

Benthic habitats of Tikhaya Bight (Hooker Island, Franz Josef Land, High Arctic) were studied by using SCUBA equipment (diving quantitative method) and Van Veen grabs. Three main communities have been described. A Gammarus setosus-macroalgae community, probably seasonal, developed above 5 meters depth, had a relatively low diversity with biomass 7.6±0.9 g/m2 and abundance 135±40 ind/m2; a mixed bivalves-amphipods-bryozoan community (Serripes groenlandicus, Mya truncata, Haploops laevis, Alcyonidium disciforme) occured in muddy bottoms with some interspersed boulders between 7 and 30 m depth; it included 101 taxons, had a relatively high biomass 152.3±114.2 g/m2 and abundance 1600±940 ind/m2. A bivalve-dominated community with Musculus niger and Yoldia hyperborean inhabited depth of 67–72 m, included 38 taxons and was characterized by high density of abundance and biomass – 670±295 ind/m2 and 356.1±57.1 g/m2, respectively. Comparison with the previous data obtained 20 years ago at the depth 7–30 m, showed that, possibly, the retreat of the glacier under the influence of increasing temperature in the environment and increased runoff of melt water, washes away clay deposits which led to siltation of the bottom in the bay and caused degradation of kelp, which was partially replaced by invertebrate communities inherent in silted soils.

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