opisthomeres n.pl. [Gr. opisthen, behind; meros, part] (AR-THRO: Insecta) In Dermaptera, the transversely divided epiproct; the so-called pygidium, metapygidium and telson.
opisthomerite n. [Gr. opisthen, behind; meros, part] (AR-THRO: Diplopoda) The gonopods of Julida; the posterior part of the modified 9th pair of legs in the male.
opisthoparamere n. [Gr. opisthen, behind; para, beside; meros, part] (ARTHRO: Insecta) In Diptera (Cyclorrhaphra), especially Calyptrata, one of two parameral processes. see proparamere.
opisthosoma n. [Gr. opisthen, behind; soma, body] 1. (ARTHRO: Chelicerata) In Acari or Ixodida, that portion of the body posterior to the legs. 2. (POGON) A terminal septate region. see protosoma, metasoma, mesosoma.
opisthosomatic appendages (ARTHRO: Chelicerata) Vestigial appendages present on the ventral regions of segments VII-XIII, such as genital papillae or valves.
opisthosomatic scissure (ARTHRO: Chelicerata) In Acari, a narrow band of skin between sclerotized plates; often transverse on the opisthosoma.
opsiblastic a. [Gr. opsios, late; blastos, bud] A delay in cleavage, and therefore a prolonged period before hatching; winter egg. see tachyblastic.
optic a. [Gr. optikos, pertaining to sight] Pertaining to the eye or sense of sight.
optical isomerism Compounds that are mirror images and differ in turning the plane of polarized light left (L-form) or right (D-form).
optic lobes Lateral extensions of the protocerebrum or nervous system for innervation of an eye.
opticon n. [Gr. opsis, sight] (ARTHRO: Insecta) The inner zone of the optic lobes.
optimum a. [L. optimus, best] The most suitable condition for the growth and development of an organism.
orad adv. [L. os, mouth; ad, toward] Toward the mouth.
oral a. [L. os, mouth] Pertaining to or near the mouth.
oral arms (CNID: Scyphozoa) In medusae, 4 or 8 often frilly oral arms, bearing cnidocytes and aid in the capture and ingestion of prey.
oral cavity The mouth; the buccal cavity.
oral cone (CNID: Hydrozoa) In polyps, a conical projection surrounded by tentacles with the mouth in the center.
oral disk (CNID: Anthozoa) In polyps, a flattened area from which, usually 8 or multiples of 6, tentacles arise that communicate with the coelenteron.
oral hooks see mandibular sclerites oral lappet (moll) Basal expansion of labial tentacles; labial veil.
oral lobe (CTENO) A muscular lobe on either side of the mouth in Lobata.
oral plate (ARTHRO: Insecta) The hypopharyngeal floor of the cibarial pump.
oral segment A ring or segment bearing the mouth.
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