Turritopsis nutricula McCrady, 1859, South Carolina, United States.
OTHER COMMON NAMES None known.
Hydroid: small colonies stolonal, monosiphonic (simple stem), larger ones erect, irregularly branched and increasing in diameter from base to apex, polysiphonic (compound stem); branches basally adnate to hydrocaulus or other branches, then curving away at an acute angle and becoming free; hy-drocaulus and hydrocladia covered by a firm bi-layered peris-arc, mostly encrusted with detritus and algae, terminating below hydranth base; hydranths terminal, naked, elongated, fusiform, with 12-38 filiform tentacles scattered over distal three quarters of column, proximal ones shorter than distal; hypostome elongated conical; medusa buds arising mostly one by one from short pedicels below hydranths, pear shaped, enclosed in perisarc.
Medusa: umbrella 0.15-0.43 in (4-11 mm) high, bell shaped to piriform, higher than wide, mesoglea thicker at apex; manubrium large, cross-shaped in transverse section, red; four radial canals passing through the four compact vacuolated endodermal masses situated above digestive part of manubrium; four-lipped mouth with a continuous row of sessile cnidocyst clusters along margin; 80-120 closely spaced marginal tentacles; gonads interradial, mature females often with developing embryos and planulae; with adaxial ocelli.
Atlantic, Indo-Pacific, and the Mediterranean. (Specific distribution map not available.)
The hydroids live in shallow, highly oxygenated water, often under overhangs. The medusae are members of the coastal plankton.
Nothing is known.
FEEDING ECOLOGY AND DIET
In the laboratory, both hydroid and medusae can survive with a diet of Artemia nauplii; the diet in the wild is unknown.
Medusae are produced by the hydroid in summer months and can survive in the laboratory for one month. A peculiarity of this species is the possibility of ontogeny reversal under laboratory conditions: the medusae, in fact, can rearrange their tissues and go back to the polyp stage if subjected to sub-lethal stress and also at the end of their lifespan, after spawning. For this reason, this medusa has been called "the immortal jellyfish" by the media.
Not listed by the IUCN.
The possibility for this species to perform ontogeny reversal in the laboratory offers a unique opportunity to study the genetic control of aging and the mechanisms of rejuvenation. ♦
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