Knobby siphonophore, Halistemma rubrum

Halistemma rubrum (Vogt, 1852)
This physonect siphonophore grows to a length of about 1 meter (about 3 feet). It was photographed in situ by the ROV Doc Ricketts in the Gulf of California at a depth of 245 meters. This species is quite common in the warmer waters of the three great oceans and, particularly, in the Mediterranean.

Siphonophores are colonial jellyfish. The small white dot to be seen at the extreme left of the animal is a gas-filled float, which helps to orient the colony. To the right of it are a number of specialised medusae, arranged biserially, whose pumping action jet propels the colony through the water. The right-hand part of the colony consists of several different kinds of individuals. The light patches are the stomachs, with their tentacles that can be seen to contract and relax. The opaque, whitish individuals are called bracts, or covering scales that serve to protect the other types of individual. Other individuals, such as the sexual medusae, both male and female, are also present, but cannot be discerned in this clip.

This video was posted to accompany the following publication:
PUGH, P. R.; BAXTER, E. J. A review of the physonect siphonophore genera Halistemma (Family Agalmatidae) and Stephanomia (Family Stephanomiidae). Zootaxa, v. 3897, n. 1, p. 1–111, dec. 2014. ISSN 1175-5334.