The gelatinous macroplanktonic organisms living in the deep sea can only be studied with manned submersibles. There is presently in increasing interest in the study of the role of this part of the pelagic ecosystem, because they are strongly involved in the transformation of the particulate organic matter. Their transparency, small size and mobility present technical challenges, unanticipated by the designers of the first submersibles, aimed at the sea bottom observation. Despite these limitations, the use of conventional submersibles has brought very interesting results. It is hoped that engineers will take into account the requirements of pelagic observations in the design of future submersibles.