Pennaria disticha, also known as the Christmas tree hydroid, is a species of athecate hydroid in the family Pennariidae. Colonies are common in the Mediterranean Sea growing on rocks close to the surface. This species has been used in research into prey capture. Colonies of Pennaria disticha consist of numerous much-branched stems up to 30 cm high. The branching system is alternate.

Pelagia noctiluca is ajellyfish in the family Pelagiidae. It is typically known in English as the mauve stinger, but other common names are purple-striped jelly (causing potential confusion with chrysaora colorata), purple stinger, purple jellyfish, luminous jellyfish and night-light jellyfish. Pelagia noctiluca can be described as a marine organism with the ability to glow in the dark (bioluminescence). It is found worldwide in tropical and warm temperate seas.

The beauty of the underwater world is that the distribution of life and various species is distributed 360° along the entire water column, even if not exactly uniformly. Marine biologists divide marine life into three macro-categories based on where they live and how they move, or rather into three marine biological categories: Plankton, Nekton and Benthos ...

We are in Sardinia in the waters of Carloforte, Isola di S. Pietro, where we met numerous purple jellyfish of the species Pelagia noctiluca. Pelagia Noctiluca ...