Apophallation is the biting off of the penis, known to occur in

terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

s, which are

hermaphroditic A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

s. It has been reported in some species of banana slugs, '' Ariolimax,'' and in the distantly related '' Deroceras laeve''. In the mating of banana slugs, the penis is inserted into the body of the partner. The penis may become trapped, perhaps because of the action of a special muscle, in which case the penis is gnawed off by either the partner or the owner. The apophallated slug can mate as a female. It has been proposed that it might be adaptive for a slug to apophallate the mating partner because that partner is subsequently prevented from mating as a male and so might increase the allocation of resources to the production of eggs fertilised from the mating. One paper reports that individuals of '' Deroceras laeve'' sometimes bite off their own penis after mating, which is then eaten by the partner. In this genus, sperm is swapped from penis to penis, so the amputee would not be able to mate successfully even in the female role.

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Reproduction in animals Gastropod anatomy Penis {{Gastropod-stub