Definitions

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Operculum

(female pleopod[s] II). — A plate over the branchial chamber of the abdomen of female janiroideans, consisting of the fused second pleopods. The first pleopods are absent in female Janiroidea. In males, pleopods I and II lock together to form an operculum somewhat similar to that Seen in the females. [Wilson, 1989]
In cirripeds, terga, scuta and associated membranes (Balanomorpha). or tergum and scutum of one side (Verrucomorpha), forming apparatus guarding aperture. [Moore and McCormick, 1969]
Scuta and terga (balanomorph) or movable scutum and tergum (verrucomorph) and associated membrane, forming apparatus occluding aperture. [McLaughlin, 1980]
(Taxon-specific: Order Decapoda) In crab-like (brachyuran) decapod, small, lid-like structure serving to close opening (excretory pore) of antennal gland. [Stachowitsch, 1992]
(Taxon-specific: Order Isopoda) Protective cover on ventral surface of abdomen (pleon); usually derived from anterior pleopod pair(s) or uropods.
See: Valve [Stachowitsch, 1992]
Balanus trigonus: apical view; left lateral view; and operculum, body, and branchiae. [Anderson, 1980]
(Taxon-specific: Subclass Cirripedia) (Figure only.) [Anderson, 1980]
(Taxon-specific: Subclass Cirripedia) In unstalked barnacle, movable, lid-like structure used to close aperture. Consists of symmetrical forms of articulated scutum and tergum closing against opposite scutum and tergum, in asymmetrical forms of movable scutum closing against movable tergum. [Stachowitsch, 1992]