Placoid sensilla see sensillum placodeum

plaga a.; pl. plagae [L. plaga, stripe] A stripe or streak of color. plagate a.

plagiosere n. [Gr. plagios, oblique; serere, to join] The succession of plant diversion into a new course by biotic factor or factors. see prisere.

plagiotriaene a. [Gr. plagios, oblique; triaina, trident] (PORIF) In tetraxons, having clads directed forward and making an angle of about 45° with the produced axis of the rhab-dome.

plagula n. [L. plagula, veil] (ARTHRO: Chelicerata) In Arach-nida, a ventral plate protecting the pedicle.

plait n. [L. plicare, to fold] 1. Longitudinally folded or laid in pleats. 2. (MOLL: Gastropoda) Applied to folds on the columella or pillar.

planaea n. [L. planus, flat] A conjectured organism in the form of a ciliated planula, purported to be a stage in the evolution of higher animals.

plane a. [L. planus, flat] 1. A smooth flat surface, devoid of markings or configurations. 2. A plasmagene or plasmid.

plane of symmetry The median plane dividing a bilaterally symmetrical animal into two halves that are mirror images of each other.

planidium n.; pl. -idia [Gr. dim. plane, wanderer] (ARTHRO: Insecta) The free-living, active, first-instar larva of some parasitic hypermetamorphic Neuroptera, Coleoptera (triun-gulin), all Strepsiptera (triungulinid), Diptera, Lepidoptera and Hymenoptera.

planipennate a. [L. planus, flat; penna, wing] Flat-winged.

planispiral a. [L. planus, flat; spira, coil] (MOLL: Gastropoda) Shells coiled in a single plane like a flat spiral with symmetrical sides; loosely used for shells whorled in a discoid form with asymmetrical sides. see isostrophic.

plankton n. [Gr. plankton, wandering] 1. Pelagic animals collectively, distinguished from coast or bottom forms. 2. A general name for animals (zooplankton) or plants (phyto-plankton) living at or near the surface of the water. see seston.

planktotrophic larva (BRYO: Gymnolaemata) Free-living, ciliated larvae with a long motile life before metamorphosis.

planoblast (CNID: Hydrozoa) The free-swimming medusa form.

planorboid a. [L. planus, flat; orbis, a circle] Flat and orb-like.

planta n.; pl. plantae [L. planta, sole of foot] (ARTHRO: Insecta) In some larval forms, an apical area of the leg bearing a row or circle of outwardly curved hooks or crochets that aid in gripping.

plantar a. [L. planta, sole of foot] (ARTHRO: Insecta) Of or pertaining to the planta or sole of the foot.

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