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BAUMILLER AND GAHN—PARASITISM ON MARINE INVERTEBRATESheavily on two important reviews of parasitism:Conway Morris’ (1981) “Parasites and the fossilrecord,” and Boucot’s (1990) “Evolutionarypaleobiology of behavior and coevolution.”We evaluated the published examples in termsof several criteria (Table 1). In considering theidentity of the parasite, if the inferred parasite wasdirectly observable in association with the host, itwas assigned to “category 1.” If the identity of theparasite was inferred from a well-constrainedproxy, namely the trace fossil that it produced, weassigned it to “category 2.” In all other instances,the identity of the parasite was considered morespeculative and assigned to “category 3.”We also considered the evidence presented forthe benefit that was gained by the parasite and forthe detrimental effects on the host. Finally, dataused to infer a long-term duration of the associationwere noted.Results.—Our search produced a substantialnumber of inferred cases of parasitism (Table 1),and, as Figure 1 illustrates, reports of parasiticassociation are quite evenly distributed through thepost-Cambrian Phanerozoic. Although slightlylower frequencies characterize the Triassic andJurassic and higher frequencies the Cretaceous andTertiary, the coarse temporal and taxonomicresolution prevents us from assigning muchsignificance to these differences, though it is worthnoting that the pattern roughly mirrors Sepkoski’s(1984) marine diversity curve. The total numberof parasitic associations for any geologic periodrarely exceeds a dozen, and if we consider thoseassociations for which the identity of the parasiteis well-constrained, based on co-occurrence orcharacteristic trace fossils (categories 1 and 2 inFig. 1), the number is lower still.To illustrate our scheme, we consider thebivalve-capulid gastropod association reported byHayami and Kanie (1980). These authors reportedspecimens of Cretaceous capulid gastropodsattached to the valves of inoceramids. Since theidentity of the interacting organisms is known, thisrepresents “category 1” in our scheme. Hayami andKanie (1980) inferred that this interactionrepresented parasitism because it was ecologicallylong-lived, as evidenced by the presence ofattached specimens, and was analogous to themodern capulids that are found in association withbivalves, gastropods, brachiopods, and annelids.Extant capulids are suspension feeders and can befacultative semi-parasites or parasites: they canFIGURE 1—Temporal distribution of reported parasites on marine invertebrates. Black, stippled, andwhite bars represent categories 1, 2, and 3, respectively. Categories 1, 2, and 3 explained in text. (Datafrom Table 1.)197