Life cycle of the jellyfish Lychnorhiza lucerna (Scyphozoa: Rhizostomeae)

Abstract

The life cycle of Lychnorhiza lucerna (Scyphozoa: Rhizostomeae) and the settlement preferences of its larvae were studied using laboratory-based rearing experiments. Mature medusae of L. lucerna were collected from the beach of the Rio de la Plata estuary, Argentina. This species displayed the typical metagenetic, (i.e. medusoid and polypoid), life cycle reported for other rhizostomes. The fertilized eggs developed into motile and short lived planulae. The majority of planulae settled on the air-water interface (p 0.05). No planulae settled on stones. Several hours after planulae settled, they metamorphosed into sessile four-tentacled scyphistomae. Most scyphistomae attached onto the air-water interface. At 19–22°C, the scyphistomae grew up to 22 tentacles and reached 1,500 μm height. The scyphistomae increased their numbers by means of formation of podocysts from which new polyps emerged and strobilated. Strobilation occurred 46 days after settlement. Only polydisk strobilation was observed and each strobila always produced three ephyrae. After releasing ephyrae, strobilae returned to normal scyphistomae and were capable of repeating strobilation. A single founder polyp was estimated to produce up to 60 ephyrae over 4 months. Ephyrae developed into metephyrae 15 days after release at 19–22°C. In this paper we describe the morphological and some behavioural features of L. lucerna in the polypoid and early medusoid stages.