Diversity, biogeography, body size and fossil record of parasitic and suspected parasitic Foraminifera; a review

We review the ecology and fossil record of parasitic and suspected parasitic foraminifera. Nine species of foraminifera are known to be parasitic, obtaining nutrients from their host, and 13 are suspected parasites that require taxonomic and ecologic work to document their trophic relationships. Roughly 0.22% and 0.32% of all benthic foraminifera are known or suspected parasites, respectively. Endo- and ectoparasites are most common, followed by kleptoparasites and putatively hermit endoparasites. While most diverse in the shallow-water tropics, the best-known foraminiferal parasites live in colder North Atlantic and Antarctic waters. Body size comparisons reveal patterns similar to parasitic metazoans: 1) a few parasitic foraminifera are larger than most benthic foraminifera and most are larger than their free-living relatives; 2) most are smaller than their metazoan hosts, but are roughly similar in size to protozoan hosts with one exception; and 3) larger parasitic foraminifera infest larger hosts, consistent with Harrison's rule. Ectoparasitic foraminifera also follow Harrison's rule, but endoparasites do not because they are spatially constrained by living within the host. Suspected foraminiferal parasites are first recorded from the Late Jurassic and parasitic foraminifera from the Early Cretaceous, while the majority evolved in the Cenozoic. Cretaceous Talpinella cunicularia has one of the longest known host-parasitic relationships of 18 Myr. Sixteen species bioerode their hosts, but only two trace fossils from parasitic foraminifera are known. Their abundance, broad geographic distribution and excellent fossil record make parasitic foraminifera and their hosts an excellent model to study how climate and environmental change affects intimately-associated species.