Ascus (bryozoa)


Ascus (bryozoa)

The ascus is a diagnostic morphological feature of the bryozoan suborder Ascophora (hence the name of the suborder). It is a water-filled sac of frontal membrane opening (ascopore) at or near the zooid orifice. It functions as a hydrostatic system by allowing water into the space below the inflexible, calcified frontal wall (covering their whole frontal surface apart from the orifice) when the zooid everts its polypide (feeding tentacles) by muscles pulling the frontal membrane inwards (non-ascophoran cheilostomes do not need this structure as their frontal wall is not calcified and thus flexible).


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  • ascus — n.; pl. asci [Gr. askos, bag] (BRYOZOA: Gymnolaemata) In ascophoran cheilostomates, the exterior walled, flexiblefloored, sac beneath the frontal shield of an autozooid; see anascan …   Dictionary of invertebrate zoology

  • parietal muscles — (BRYOZOA) Generally multiple, bilaterally paired muscles that insert on the front wall or floor of the ascus; usually functioning in the hydrostatic system …   Dictionary of invertebrate zoology

  • moss animal — bryozoan. [1880 85] * * * ▪ invertebrate Introduction also called  bryozoan,         any member of the phylum Bryozoa (also called Polyzoa or Ectoprocta), in which there are about 5,000 extant species. Another 15,000 species are known only from… …   Universalium

  • Ascophora — Taxobox name = Ascophora fossil range = Late Cretaceous Recent regnum = Animalia phylum = Bryozoa classis = Gymnolaemata ordo = Cheilostomata subordo = Ascophora subordo authority = Levinsen, 1909 subdivision ranks = Infraorders subdivision =… …   Wikipedia

  • Anasca — was a bryozoan sub order under class Cheilostomida defined by the lack of an ascus in each zooid. It is no longer an accepted taxonomic grouping as it is considered a polyphyletic and/or paraphyletic grouping. The group is now subdivided into the …   Wikipedia

  • Phylum — For other uses, see Phyla …   Wikipedia

  • anascan — n. [Gr. an, without; askos, sac] (BRYOZOA: Gymnolaemata) Cheilostomata in which the autozooids have a hydrostatic system including the flexible part of the frontal wall, thus lacking an ascus …   Dictionary of invertebrate zoology

  • ascopore — n. [Gr. askos, bag; poros, channel] (BRYOZOA: Gymnolaemata) In some Cheilostomata, a small opening in the frontal wall connecting the ascus to the external environment …   Dictionary of invertebrate zoology

  • spiramen — n. [L. spiramen, vent] (BRYOZOA) A median pore, not connected to the ascus, in the frontal wall on the proximal side of the orifice …   Dictionary of invertebrate zoology


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