THE CULTURE, SEXUAL AND ASEXUAL REPRODUCTION, AND GROWTH OF THE SEA-ANEMONE NEMATOSTELLA-VECTENSIS

Nematostella vectensis, a widely distributed, burrowing sea anemone, was raised through successive sexual generations at room temperature in non-circulating seawater. It has separate sexes and also reproduces asexually by transverse fission. Cultures of animals were fed Artemia sp. nauplii every second day. Every eight days the culture water was changed, and the anemones were fed pieces of Mytilus spp. tissue. This led to regular spawning by both sexes at eight-day intervals. The cultures remained reproductive throughout the year. Upon spawning, adults release either eggs embedded in a gelatinous mucoid mass, or free-swimming sperm. In one experiment, 12 female isolated clonemates and 12 male isolated clonemates were maintained on the 8-day spawning schedule for almost 8 months. Of the female spawnings, 75% occurred on the day following mussel feeding and water change, and 64% of the male spawnings were similarly synchronized under this regime. Fertilization and development occur when gametes from both sexes are combined in vitro. At 20-degrees-C, the embryos gastrulate within 12-15 hours. Spherical ciliated planulae emerge from egg masses 36-48 hours post-fertilization. The planulae elongate and form the first mesenteric couple, as well as four tentacle buds, by day five. By day seven, they metamorphose and settle as 250-500 mum long, four-tentacled juvenile anemones. More tentacles and all eight macrocnemes are present at 2-3 weeks. Individuals may become reproductively mature in as few as 69 days. Nematostella vectensis has the potential to become an important model for use in cnidarian developmental research.