Laboratory observations on reared life stages of Chironexfleckeri (Cubozoa: Chirodropidae) have been combined with field sampling and observations to outline the life cycle of the species and the spatial and temporal distribution of populations in Queensland, Australia. A seasonal alternation of polypoid and medusoid generations from winter to summer respectively is accompanied by a shift in preferred habitat from tidal estuaries to the open eulittoral zone. The system appears to be constrained by predictable fluctuations in the suitability of the alternate habitats to their resident generations. Observations on behaviour, feeding, physiological tolerances, and sexual and asexual reproduction provide insights into the adaptiveness of this pattern.

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Substantial numbers of the very small carybdeid jellyfish, Carybdea sivickisi, have been observed feeding actively by divers in the vicinity of fringing coral reefs. During the day specimens were seen in close association with the substrate and with sessile macroalgae. They appeared able to adhere to substrates by contact with an area on the aboral surface of the bell. Individuals maintained in the laboratory showed the same adhering ability. The adhesive organs correspond to 4 areas of raised secretory epithelium on the aboral surface.Following capture, one isolated specimen extruded a long gelatinous strand containing several thousand developing embryos and numerous functional nematocysts. The embryos developed into characteristic cubozoan planulae, which were able to attach themselves temporarily to substrates by means of nematocysts. After 4 days of free swimming, planulae began to attach permanently and to develop into sessile polyps with 3 or 4 tentacles, each armed with a single stenotele.The species displays sexual dimorphism and evidence for spermatophore formation and transfer which parallel that reported for Tripedalia cystophora. The presence of sperm-storage sacs in both sexes, the production of an embryo mass, the adhering behaviour and an apparent association with algal substrates are among features apparently unique to the species.

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