onychium n.; pl. -ia [Gr. onyx, claw] (ARTHRO: Insecta) A general term for a pad between the tarsal claws.
Onychophora, onychophorans n.; n.pl. [Gr. onyx, claw; phorein, to carry] A phylum of terrestrial animals comprised of a single class or order of the same name, frequently referred to as Peripatus ; once considered to be the missing link between annelids and arthropods, but now considered to be the sister group of the arthropod complex of Crustacea, Tracheata, and Chelicerata.
ooblast n. [Gr. oion, egg; blastos, bud] A cell from which an ovum develops.
ooblastema n. [Gr. oion, egg; blastos, bud] A fertilized egg; an oosperm.
oocapt n. [Gr. oion, egg; L. captus, capture] (platy: Cestoda) A controlling spincter of the oviduct that allows mature oocytes to enter the proximal oviduct.
oocyst n. [Gr. oion, egg; kystis, pouch] The cystic form in the parasitic protozoans (Apicomplexa), resulting from sporog-ony; may be hard covered, with a resistant membrane (Eimera) or be naked (Plasmodium).
oocytes n.pl. [Gr. oion, egg; kytos, container] An immature female gamete that undergoes meiosis, giving rise to ova or eggs.
ooecia n.pl.; sing. -ium [Gr. oion, egg; oikos, house] (BRYO: Gymnolaemata) In Cheilostomata, the outer protective part of an ovicell; sometimes thought to be zooid morphs; a brood pouch.
ooecial vesicle (BRYO: Gymnolaemata) In Cheilostomata, an inner membrane of an ooecium.
ooeciostome n. [Gr. oion, egg; oikos, house; stoma, mouth] (BRYO: Stenolaemata) The gonozooidal orifice, may or may not have peristome surrounding the aperture of ovicell.
oogamy n. [Gr. oion, egg; gamos, marriage] The union during fertilization of a nonmotile female gamete and a motile male gamete. oogamous a. see anisogamy, isogamy.
oogenesis n. [Gr. oion, egg; genesis, beginning] The development of the female egg cell or ovum that takes place in the gonad.
oogenotop n. [Gr. oion, egg; genesis, beginning; topos, place] (PLATY: Cestoda) A small cellular complex following the oviduct within the female reproductive system where shell membranes form, enclosing the zygote and several vitelline cells. see columella.
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