Definition of osculum in US English:



  • A large aperture in a sponge through which water is expelled.

    • ‘In budding, aggregates of cells differentiate into small sponges that are released superficially or expelled through the oscula.’
    • ‘The hole closes and it is not until some days later that the sponge forms an osculum at its apical pole.’
    • ‘Sponges will react by closing ostia or oscula, either because of direct physical stimulation or when suspended particles within the sponge are too large or highly concentrated.’
    • ‘Spicules first appeared 2 days after release from the parent and an osculum was first seen in 9-day old settled juveniles.’
    • ‘Syconoid sponges tend to be larger than asconoids and have a tubular body with a single osculum.’


Early 17th century: from Latin ‘little mouth’.