Definition of operculum in US English:

operculum

noun

Zoology Botany
  • 1A structure that closes or covers an aperture.

    • ‘Therefore, the operculum is always visible in complete specimens.’
    • ‘In amphibians the inner ear is mechanically coupled to the pectoral girdle through the operculum.’
    • ‘It is able to withdraw the whole of its body into its shell which is then sealed by an amber-coloured operculum.’
    • ‘Whenever muscular control of the operculum was established (presumably very early), it was probably based on the cleithrum.’
    • ‘The archeopyle is created by loss of an operculum that is distinguished from the adjacent cyst surface by a distinct groove.’
    1. 1.1
      technical term for gill cover
      • ‘The nape lacks cirri, and the first gill arch attaches to the operculum, the latter characteristic distinguishing Tripterygiidae from Clinidae.’
      • ‘Due to the close proximity of the operculum and the pectoral fins, water jetting out of the operculum could affect flow over the pectoral fins, possibly changing locomotory efficiency.’
      • ‘In amphibians the inner ear is mechanically coupled to the pectoral girdle through the operculum.’
      • ‘On the bottom of their operculum or gill-cover, they have a sharp spine. Angelfish all vary in color and pattern.’
      • ‘These fish do not have gills or opercula (gill coverings) like most bony fishes.’
    2. 1.2 A secreted plate that closes the aperture of a gastropod mollusk's shell when the animal is retracted.
      • ‘Many snails have an operculum, a horny plate that seals the opening when the snail's body is drawn into the shell.’
      • ‘From the shape of Macluritid opercula, we know that Macluritids are dextral shells with a depressed (sunken or downward pointing) spire, not left-handed shells with a normal elevated one.’
      • ‘They inhabit salt marshes near the sea, and are able to seal the shell with the operculum and so survive dry periods buried in mud.’
      • ‘Immobilizing snails caused them to draw their operculum deep within their shell, which may have restricted the crabs' ability to extract the flesh from the shell, even with extensive apertural breakage.’
      • ‘Above the head and the arms is a leathery, protective hood, that acts like an operculum to protect the animal when it withdraws inside its shell.’
    3. 1.3 A lidlike structure of the spore-containing capsule of a moss.
      • ‘As the spores grow, fluid pressure builds up in the ascus until the operculum bursts open and the ascospores are blown out into the environment.’
      • ‘The sporophytes also develop opercula, peristomes, continuous columella, and a spongy layer between the amphithecium and the spore mass.’

Origin

Early 18th century: from Latin, literally ‘lid, covering’, from operire ‘to cover’.

Pronunciation

operculum

/ōˈpərkyələm//oʊˈpərkjələm/