Traveling Anenomes

Folks,

Thought that you might be interested to see this shot, taken in St. Vincent last week of a tiny hermit crab, and passengers. I have not seen anything like this, so would love some input... can anyone ID the anemones?

The shell of the crab is about the size of a pea, approx 1 cm across. The grains of sand should give an idea of context.

Your assistance is very much appreciated and always!

http://www.facebook.com/photo.php?pid=8993...;id=86847095454

Thanks in advance.

Kay Wilson,

Indigo Dive,

St. Vincent.

I think your "Anemones" are actually hydroids.

Hi Kay - I agree with Will in that the "anemones" which are attached just under the rim of the shell are probably hydroids. Are those other cnidarians on the right also attached? There are many cnidarians which are specialized hermit-crab associates, and some of them will only associate with one species of hermit. It's also common for a crab to carry 2 or more species - one on the outside of the shell, one just under the rim, and sometimes one species tucked deep inside the shell which feeds on the crab's feces. Yuck! And then there are hydroid species like Hydractinia echinata which completely cover the outside of the shell.

Here's some interesting reading on the subject --

HERMIT CRAB - CNIDARIAN ASSOCIATIONS IN THE NORTHERN GULF OF MEXICO (SYMBIOSIS, CALLIACTIS, HYDRACTINIA).

Creator BROOKS, WILLIAM RANDALL.

Abstract The associations of hermit crabs with two groups of Cnidaria, sea anemones (Actiniaria) and hydroids (Hydroida), in the northern Gulf of Mexico, were studied.

Two populations of the hermit crab, Pagurus pollicaris, were behaviorally distinct in that one population transferred significantly more anemones (Calliactis tricolor) to their gastropod shells than did the other. Both populations of P. pollicaris and one population of another hermit crab, P. impressus, transferred fewer C. tricolor after four weeks in an aquarium than they did in their first week. The chemical presence of the octopus, Octopus joubini, however, increased the number of anemone transfers by both species of hermit crab. The more active anemone-transferring population of P. pollicaris was collected from an area with a greater density of O. joubini than the area of the less-active population. Therefore, the differences between the two populations of P. pollicaris may have been due in part to differences in predation pressure (i.e., by O. joubini or other predators).

The shell entry and shell selection of two populations each of P. pollicaris, P. longicarpus, and Clibanarius vittatus, for hydroidcolonized (either Hydractinia echinata or Podocoryne selena) shells was observed under various conditions. All three species either initially chose or subsequently switched into bare shells, even in the presence of a predator. The population of P. pollicaris where O. joubini was more abundant selected hydroid-colonized shells more frequently in one experiment than did the other population of crabs.

The hydroid-colonized shell was a deterrent to predation by the stone crab, Menippe mercenaria, and O. joubini. Predation by the calico crab, Hepatus epheliticus, was not deterred by a hydroid colony on the shell inhabited by P. pollicaris.

The anemone, C. tricolor, and the hydroids rarely co-occur on the same gastropod shell. Contact and subsequent cnida discharge by the anemone and the hydroids significantly contribute to their negative association.

Previously, it was unknown how C. tricolor reproduced. The present study reports the discovery of a C. tricolor anemone that was undergoing longitudinal fission.

Thesis (Ph.D.)--The Florida State University, 1984.