Pleurobrachia pileus, (50 cm.)
Supervised by Thomas Schaarschmidt.
Pleurobrachia pileus is a species of comb jelly, commonly known as a sea gooseberry. It is found in open water in the northern Atlantic Ocean, the North Sea, the Baltic Sea and the Black Sea.
The sea gooseberry is a small, globular comb jelly that grows to about 2.5 cm in length. It has a pair of long tentacles that are used to catch prey and can be retracted into sheaths. The tentacles are up to twenty times the length of the body and are fringed with filaments along one edge. The body bears four pairs of longitudinal rows of cilia, that looks like combs. These cilia extend about three quarters the length of the animal, and are mounted on bioluminescent plates on the animal. It is the beating of the cilia in synchrony that allows the animal to swim and that gives it an iridescent appearance. The body is transparent and the comb rows milky white. The tentacles, sheaths and pharynx are also milky white, or dull orange in some individuals
Pleurobrachia pileus makes large daily vertical migrations up and down the water column. They spend the night in upper waters, usually just below the thermocline, descending to deep waters between 80 and 150 metres in the early morning, and rising again in late afternoon.