Velum

The term, velum, derived from Latin "velum", meaning a "sail", "curtain," "awning" or "veil", has several quite separate meanings in biology:

* the locomotory and feeding organ provided with cilia found in the larval stage called the veliger or "velum-bearing" stage of bivalves, such as mussels and oysters; also a delicate membrane found on certain Protists.

* the circular membrane around the cap of a sea jelly or medusa, of class Hydrozoa, which helps with propulsion

* the veil-like membrane of immature mushrooms extending from the margin of the cap to the stem and torn by growth, revealing the gills of a mature sporophore; in a mature mushroom, the remains of the velum may form an "annulus" or ring around the stem, familiar from common button mushrooms and sometimes on the margin of the cap.

* the soft palate behind the hard palate

* the superior medullary velum

* a thin flap of tissue completely or partially covering the adaxial wall of the sporangium in species of Isoetes

* Velum is also a common misspelling of vellum, calfskin (or sometimes the skins of other animals) that is similar to parchment and that is used as medium for writing, book printing, and book binding. Today, leatherette, leather, cloth or paper are more commonly used, but vellum is still used occasionally.