Ring sea anemones, an overview (Cnidaria, Anthozoa, Actiniaria)

Abstract

The present observations represent a new record of species of Actiniaria that are able to attach to a gorgonian branch by surrounding it with a solid piece of tissue junction and a significant reduction of the coelenteron. Ring sea anemones are provisionally placed in the Actinostolidae. They seem to be more common at depths between 85 and 1500 m., and according to our observations they are speciali- zed to exclusively colonize on some species of gorgonians or pennatulaceans. Parasitism best describes the relationship between ring sea anemones and their hosts. We recognize five different species of ring sea anemones, one described by Hiles (1899) as Peronanthus verrucellae, and the others named by us provisionally as Peronanthus sp1, sp2, sp3 & sp4. The strategy displayed by ring sea anemones has several advantages, such as placement economy (see above), a better attachment against any current action, exploitation of food resources inaccessible to most other Actiniarians, and it allows them avoi- dance of habitat competition. The impossibility to colonize any other substrate but a certain group of gorgonians and a reduction of the gastric cavity are the main disadvantages detected in the ring sea ane- mones’ way of life. Apparently, this group of sea anemones is widespread through the Pacific Ocean.