Critter of the week: Calliactis polypus – pumice hitchhiker
This spectacular anemone, probably Calliactis polypus (Forsskal, 1775), was seen hitching a ride on a piece of pumice floating in the sea near Burgess Island in the Mokohinau group off the northeast coast of New Zealand.
This photographed by NIWA principal technician Crispin Middleton. Crispin is an expert diver and underwater photographer. He noted that the anemone was “large, probably about 60-80 mm across the base and about 100 mm tall when open and extended”.
We asked our international anemone expert Professor Daphne Fautin at the University of Kansas for some help to identify it. Prof. Fautin believes it to be from the genus Calliactis due to the dots around its base, which are characteristic of the genus. She told us that the dots around the base are holes through which defensive acontia can be shot. Acontia are threadlike organs composed of stinging cells. Calliactis is commonly a symbiont living on the shells of hermit crabs, but it is known to attach to other objects, so being attached to pumice in not unusual.
Daphne says the taxonomy of the Calliactis genus has been long debated.
“There are clear differences among specimens from across the Pacific, but there are no clear boundaries. The ends of the spectrum differ but it is all a [blur] in between, so it is not obvious where lines, if any, should be drawn. Thus it is not a rare species, and this sort of transport may be the reason there seems to be a taxonomic [blur] across the Indo-Pacific.”
The species Calliactis parasitica is found in European waters and the name C. polypus is commonly used for the Indo-Pacific species. So while there is some debate about the taxonomy of the species in this genus, at this stage we think it is likely to be polypus. This a new record for New Zealand waters and is an interesting addition to our knowledge of fauna transported around by pumice.