Practice question

A hermit crab occupying a dead snail shell exemplifies metabiosis, a form of commensalism in which one organism uses a structure or environmental modification left by another after the producer has died or departed. The crab gains protection for its soft abdomen, while the former snail cannot be affected; there is no continuing reciprocal exchange. Tapeworms are parasites, ants and aphids are mutualists, and epiphytes on living trees illustrate support-based commensalism or inquilinism. The keyed example is therefore biologically appropriate for metabiosis. However, “metabolic commensalism” is not the standard name for shell reuse. In microbiology, metabolic commensalism can describe one organism consuming another’s waste products without affecting the producer, which is a different mechanism. The likely intended term is “metabiosis,” not “metabolic.” Reusing an abandoned structure also differs from phoresy, because no living carrier transports the crab. KEY MISMATCH: the answer example fits metabiosis, but the question’s technical label is erroneous and should not be treated as an accepted synonym.