Tharyx marioni (Polychaeta): a remarkable accumulator of arsenic

Analyses of the cirratulid polychaete Tharyx marioni have shown that this species contains a high concentration of arsenic, its whole-body concentration usually exceeding 2000 μg/g dry weight, even when living under low ambient arsenic conditions. Similar levels of arsenic are present in both juvenile and adult worms. Other cirratulid species, such as Cirriformia tentaculata and Caulleriella caputesocis , from the same habitat contain low arsenic concentrations (< 100 μg/g dry weight). Much of the arsenic in T. marioni ( ca . 20 %) is contained in the palps which comprise about 4% of the body dry weight; in these organs, concentrations of 6000–13 000 μg/g dry weight have been measured. Some of the arsenic in the palps is bound with copper in granules but the bulk appears to be organically associated; extraction data indicate about 65% of the total arsenic is linked to the lipid pool with a further 25% being proteinbound arsenite (cysteine-extractable). The results of experiments using 74 As suggest that most of the arsenic is derived from the sediments rather than the water but the mechanisms and functions of this arsenic accumulation by T. marioni remain to be investigated.