Red siphonophore, Stephanomia amphytridis

Stephanomia amphytridis (Lesueur & Petit, 1805)
This physonect siphonophore probably grows to lengths of 10 metres or more, although only 15-20 cm in diameter. The first known record for this species was published in 1805 and it consisted only of a drawing of a small part of a specimen, including the orange stomachs to be seen in the video, that probably had detached from its tail end. Although there have been several subsequent descriptions purporting to be this species, most actually refer to another physonect species, and the paper by Pugh & Baxter (2014) is the first time that this species has been fully described.

The video shows the typical features of a physonect siphonophore, which are highly polymorphic colonial coelenterates. The colony can clearly be divided into to sections. The anterior section consists of biserially arranged opaque swimming bells. Their function is, by their co-ordinated pumping action, to propel the colony through the water. At the free end of this region, called the nectosome, can be seen a small white float that serves to orient the colony. The major proportion of the colony, the siphosome, includes several types of individual, such as the large stomachs that hang down from the stem and the opaque individuals are bracts, or covering scales, that serve to protect the other individuals. There are also sexual medusae with each colony being either male or female.

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.