The rare siphonophore Rhizophysa eysenhardtii Gegenbaur, 1859 (Hydrozoa, Siphonophora, Cystonectae) from False Bay, South Africa

Abstract

From June to September 2022, five colonies of the rare hydrozoan siphonophore Rhizophysa eysenhardtii were observed for the first time near the surface in False Bay, South Africa. The two colonies in June/July were small with all tentacles contracted, while the September colonies were larger, the largest up to 0.8 m long (in video), with most of its tentacles extended for feeding. In this species, tentacles are typically pink and each arises from the proximal end of a gastrozooid, which engulfs and digests the prey. Fish larvae were noted in the gastrozooids and counted and a chaetognath was observed stuck to one of the tentacles. The pneumatophore was prominent in all specimens and gonodendra bearing sexual gonophores were visible between the gastrozooids of the larger specimens.