labellum; lip (of an orchid flower)
Botanical term for the specialized petal of an orchid or similar flower, often used for attracting pollinators.
velum (of a mollusc or medusa)
Zoological term for a membrane or lip-like structure in certain invertebrates, such as the velum of a mollusc larva or the marginal structure of a jellyfish.
The labellum of this orchid is a vivid purple.
Mollusc larvae swim using the velum.