Observations on the anatomy, behaviour, reproduction and life cycle of the cubozoan Carybdea sivickisi

Abstract

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.