Bud formation and metamorphosis inCassiopea andromeda (Cnidaria: Scyphozoa): A developmental and ultrastructural study

Abstract

Abstract.Asexual reproduction by formation of swimming buds which metamorphose directly into polyps plays a most important role in the propagation of Cassiopea andromeda (Cnidaria: Scyphozoa). (C. andromeda polyps, originally supplied by the LSbbecke Museum and Aquarium Dtisseldorf, FRG, were cultured in our laboratories.) We have defined five budding stages and investigated epithelial recruitment and dynamics during bud formation using intracellular vital stains. The region of cell recruitment was found to encircle the budding site asymmetrically. The aboral side contributing considerably less to the developing bud than the oral and lateral sides. Furthermore, it was found that the epithelial flow involved in bud formation is part of a permanent apico-basal displacement of ectodermal cells. Light and electronmicroscopic investigations revealed that no drastic changes occur at the cellular level, neither in the ectoderm nor in the endoderm which both participate in bud formation. Scanning and transmissionelectron microscopic investigations of the swimming bud revealed that the ectoderm is composed of three, and the endoderm of two, cell types. Nerve elements have been detected near the mesoglea between both ecto-and endodermal cells. Amoebocytes are regularly found either at the basis of epidermal cells or within the mesoglea, whereas symbionts are located in the endoderm. Buds induced to metamorphose by a bacterial-inducing factor were used to investigate morphological and ultrastructural changes occurring during metamorphosis and scyphistoma morphogenesis. Metamorphosis starts with the settling of a bud, followed by the formation of the pedal disk in which desmocytes, as typical cnidarian adhesive structures, are differentiated. Metamorphosis is completed with the formation of the mouth and tentacles. Whereas metamorphosis of cnidarian planulae implies considerable changes at the cellular level, tissue remodeling processes prevail in bud metamorphosis of C. andromeda.

Planulae brooding and acquisition of zooxanthellae inXenia macrospiculata (Cnidaria: Octocorallia)

“…Pardy & Muscatine (1973) have demonstrated that during the reestablishment of the symbiosis between aposymbiotic green hydra and Chlorella, the algae are taken in by phagocytosis of gastrodermal cells. Hofmann & Honegger (1990) have shown that zooxanthellae are occasionally found in the swimming buds of Cassiopeia andromeda. The microalgae are located within the mesoglea or between the bases of the endodermal ceils.…”

A system for mass culture of Upside-down jellyfishCassiopeaspp as a potential food item for medusivores in captivity

“…The polyps that release the ephyrae should be cultured in a separate tank with an optional catch basin. The attached polyp of Cassiopea spp will release freeswimming buds that metamorphose into new polyps (Hofmann & Honegger, 1990). The polyps should be kept separate from the grow-out system otherwise they may colonize it and polyps are able to sting the medusae they propagate (Sommer, 1992).…”

Revised descriptions of the nematocysts and the asexual reproduction modes of the scyphozoan jellyfish Cassiopea andromeda (Forskål, 1775)

“…The medusa lays with its umbrella surface (exumbrella) toward the ground, while the oral arms are stretched into the water column to catch zooplanktonic prey. This also provides the endosymbiotic zooxanthellae (dinoflagellates of the species Symbiodinium microadriaticum Freudenthal, 1962) that can be found in the epithelial layer of the animal with sunlight and in turn contribute photosynthates to the jellyfish (Rahat and Adar 1980;Hofmann and Kremer 1981;Hofmann and Honegger 1990;Hofmann et al 1996).…”

“…After fertilization, eggs develop into planula larvae in the center of the female's oral disc (Gohar and Eisawy 1960;Hofmann et al 1996). Released planulae settle on hard substrates and develop into asexually reproducing polyps that show two typical modes of asexual reproduction: (1) the formation of swimming buds metamorphosing into additional polyps after settlement and (2) monodisc strobilation, during which the upper polyp body undergoes transverse fission releasing a single juvenile medusa, called an ephyra (Hofmann et al 1978;Hofmann and Honegger 1990;Hofmann and Gottlieb 1991).…”