prevents removal by the host.

Evolution

Siphonal indentations have evolved multiple times in gastropods and are widespread among many clades. Euomphanilae gastropods in the genus Scalites developed siphons in the early Ordovician period (448-443 MYA); however, they are not observed in any other members of the clade. 22 of an estimated >23 instances of siphonal indentations evolved in Murchosinoniinae gastropods - the two major clades in this group are Vetigastropoda (1 siphonate group:

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