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.

Sexually Dimorphic Cubomedusa Carybdea sivickisi (Cnidaria: Cubozoa) in Seto, Wakayama, Japan

“…In this study, in all but one male with a bell diameter greater than 4.0 mm, these orange patches had developed into a pair of flattened hemigonads, which were pinched in at the perradius. In larger males, the paired hemigonads contained an orange pigmented structure filled with sperm (see Hartwick, 1991;Fig. 1C).…”

“…These sacs have dark orange pigmentation and appear to function as sperm-storage organs: spermathecae in females and seminal vesicles in males (Hartwick, 1991;Lewis and Long, 2005; observations detailed below).…”

“…Carybdea sivickisi Stiasny, 1926 is a relatively small, sexually dimorphic cubomedusa, up to 14 mm in diameter, with four distinctive adhesive pads that stick the animal to algal substrates during the day (Hartwick, 1991;Lewis and Long, 2005). Mature females display leaf-life gonads (2 per quadrant), while male gonads are in the form of two orange-tinted sperm-filled hemigonads per quadrant.…”

Internal fertilization and sperm storage in cnidarians: a response to Orr and Brennan

“…These tiny box jellyfish display sexual dimorphism and courtship behavior in which spermatophores are formed by coalescing sperm packets ejaculated from 'seminal receptacles' of the male testes (called hemigonads) [8][9][10][11]. Testes are depleted with successive ejaculations during breeding experiments, becoming visibly paler, but sperm content is replenished the next day for subsequent copulations.…”

“…In C. sivickisi both polyandry and polygyny are pervasive [8], suggesting sperm competition and opportunities for postcopulatory female choice. Sperm is pigmented (orange or red) ( Figure 1) providing an observable cue when sperm disperses from the stomach into the gastrovascular cavity, facilitating internal fertilization within hours to days, after which time the female deposits an embryo strand (unique among cnidarians) onto the substrate [8,10]. One documented change induced by copulation in C. sivickisi is the presence of conspicuously dark pigmented velarial spots in sexually active females, which are absent in juvenile females and all males [8].…”