Repeating rejuvenation in Turritopsis, an immortal hydrozoan (Cnidaria, Hydrozoa)

Abstract

Repeating rejuvenation of Turritopsis sp. from medusa to polyp was observed 10 times, which is the most numerous number of such a reversal life cycle. Starting from a single immature medusa collected from Okinawa Island, southern Japan in May 2009 as a founder, every rejuvenated hydroid colony was continuously cultured for about two years, being kept separately in respective tank filled with fresh natural seawater (32 psu) at Shirahama, Wakayama Prefecture, Japan in a running seawater system in the laboratory at 21-29 ℃ without strong natural sunlight which may induce algal growth on rearing vessels, and being fed mainly with Artemia nauplii.