Symbiosis: Amphiura - Eulimidae (parasitism)

Amphiura joubini: host
Eulimids: endoparasite

In a Amphiura belgicae specimen, caught in South Georgia, Mortensen (1936) described a gastropod that could belong to the same species as the one from the present study. Mortensen described as a possible mechanism of parasite infestation its entrance through an orifice. He also indicated that the adult looked like a sack and had no visible shell.

In the examined specimens of Amphiura joubini from South Shetland we can  see externally one or two large whitish interradios. When we opened the animals, we saw a bag with numerous white or flesh colored shells inside the coelom, the adult being globular.

There is no observable orifice through which the gastropod entered, so there is a possibility of its regeneration. However, in one of the specimens that had two parasites in contiguous interradios, the other interradios are open ventrally, which leads us to think that this would be an “exit” mechanism for the gastropods.
This parasitism does not necessarily mean the death of the brittle star, possibly due to its great regenerative capacity. Although this is only a supposition, based on the large number of examined specimens of Amphiura joubini with badly damaged interradios due to the process of youth parasitic forms leaving their host.
There have also been numerous open specimens of Ophiolimna antarctica, without most of the aboral disk, it is hard to find a “whole” specimen in our collection. In one of the specimens a pair of juvenile gastropods were found, so it does not seem to be a specific Amphiura genus parasitism.
Although there is a reference in the literature on the presence of internal eulimidae parasites, not yet been identified at specific level (Anders Waren, pers. Comm.)

Live Amphiura jouvini

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