The longest-living animal on Earth is the Turritopsis dohrnii jellyfish. It is a small jellyfish with a bell-shaped body, about 4-5 millimeters in diameter. Its transparent body allows the red digestive system to be seen, resembling a lighthouse, hence its name. The Turritopsis dohrnii has a large, bright red stomach with a cross-shaped cross-section. It mainly lives in tropical waters. It is carnivorous, feeding on plankton, small crustaceans, polychaetes, and even small fish. The Turritopsis dohrnii can reproduce asexually from a polyp stage and is the only known organism capable of reverting from sexual maturity to a larval stage. Reaching sexual maturity takes 25 to 30 days at a water temperature of 20°C.
The Turritopsis dohrnii is a small jellyfish. Its body is bell-shaped, about 4-5 mm in diameter, and transparent, revealing its red digestive system. Resembling a lighthouse, it gets its name from this. The diameter and height of its bell-shaped body are roughly equal. The convex side is called the exumbrella, and the concave side is called the hypoumbrella. A drooping tube called the lip is located in the center of the hypoumbrella, with the mouth at its free end. A ring of tentacles surrounds the edge of the bell. In the Turritopsis dohrnii, a narrow membranous structure called the marginal membrane extends inward from the edge of the hypoumbrella; the marginal membrane is a characteristic feature of hydroid jellyfish. The body wall consists of two layers of epithelial muscle cells with a mesoglea sandwiched between them. Four radial canals extend from the gastric sac towards the bell edge, connecting with a ring canal parallel to the bell edge. Centrifugal canals also extend from the ring canal into the tentacles, reaching their tips. Sensory organs, such as eyespots or steatus sacs, are located at the bell edge or the base of the tentacles. The Turritopsis dohrnii has a large, bright red stomach with a cruciform cross-section.
