Skin-digging tanaids: the unusual parasitic behaviour of Exspina typica in Antarctic waters and worldwide deep basins

The order Tanaidacea includes over 1000 species which are mainly free-living or tube-dwelling detritivores. Exspina typica Lang, 1968 represents an exception to these common life styles, having being found in the intestine and body cavity of deep sea holothuroids. The 2008 New Zealand 'IPY-CAML Cruise' held in the Ross Sea collected several deepwater holothuroids that were observed to carry specimens of E. typica inside their coelomic cavity. A clear interpretation of this association was hence possible. Even if E. typica shows slight adaptations to a parasitic life style, the tanaids were found to actively 'dig' into the host's skin, grasping tissue with their claws and producing tunnels in the body wall. It is therefore possible to clearly define this association, which is here reported from the Antarctic for the first time, as parasitism.