Turritopsis rubra

Adult medusae are energetic swimmers. They are 3–7 mm in diameter, with a bell-shaped, transparent umbrella. The margin of the umbrella has a fringe of up to 120 closely-spaced, long, thin tentacles which coil up or extend out in strings to catch small planktonic animals to feed on.[2] The tentacles have adaxial ocelli. The bright red or red-orange stomach and the gonads can be seen.[1] They cannot sting humans as their stings are too small.[3]

As a hydrozoan, T. rubra has two distinct stages in their life, a polyp stage and a medusa stage. Polyps grow in benthic colonies and asexually reproduce to create medusae, which are free-swimming, dieocious, and reproduce sexually.

Female medusae brood their larvae, sometimes up to the primary polyp stage. The larvae are small and free-swimming and develop into polyps which form colonies when they find a hard substrate to live on. The polyps branch out stolons which reach 15 mm out (up to 50 mm in very large colonies), and are 160–200 μm in diameter[4]. Colonies are initially stolonial, then later upright as stolons attach and ramify. The polyps themselves are intensely orange red. They have a conical hypostome surrounded by 12–20 threadlike tentacles up to 0.6 mm long. Underneath the polyp is the perisarc, which is firm, usually heavily infested with detritus and algae, and double layered, the second layer corrugated. When stressed, the polyp contracts into an egg shape, but it cannot retract into its perisarc.

Polyps asexually reproduce to create medusae buds, which grow on the perisarc covered region from short stems. Usually one bud grows per region.[1]

Turritopsis rubra has a South Pacific distribution and has been recorded around New Zealand and southern Australia, including around Tasmania.[1] Swarms of medusae can be abundant in summer in shallow, coastal waters.[2]

T. rubra was one of the species of the genus Turritopsis formerly classified as T. nutricula, including the "immortal jellyfish" (now classified as T. dorhnii). However, based on morphological and life cycle differences, Schuchert (2004)[5] considers this New Zealand turritopsis to be distinct from the eastern Atlantic T. nutricula. T. rubra is practically indistinguishable from the European T. polycirrha, except for being ghonochroistic.