periostracal glands (MOLL: Bivalvia) Glands of the mantle edge that secrete the base layer of the periostracum.
periostracal groove (MOLL: Bivalvia) The groove between the tentacular fold and the shell fold that houses the periostra-cal glands.
periostracum n. [Gr. peri, around; ostrakon, shell] A thin skin or horny covering on the exterior of the shells of most Mollusca and Brachiopoda. periostracal a.
periparturient period That period before, during and after giving birth.
periphallic organs (ARTHRO: Insecta) Genital processes on the posterior ventral surface of segment 9.
peripharyngeal ganglion (BRYO) Prolongation of the cerebral ganglion around the oral opening.
peripheral a. [Gr. peri, around; pherein, to carry] To or toward the surface; distant from the center.
peripheral nerve net (NEMATA: Adenophorea) A subcuticular neural meshwork that connects the setae and papillae on the whole body surface of some marine forms.
peripheral nervous system Contains all sensory cell bodies (exceptions rare), plus local plexuses in the body wall or viscera, local ganglia of either sensory or motor-and-inter-nuncial composition, plus the pheripheral axons making up the nerves.
periplasm n. [Gr. peri, around; plassein, to mold] (ARTHRO: Insecta) A bounding layer formed by cytoplasm in the egg that lies just beneath the vitelline membrane and completely surrounds the egg.
peripneustic a. [Gr. peri, around; pneustikos, of breathing] (ARTHRO: Insecta) Having 9 pairs of functional spiracles; usually a prothoracic pair and 8 abdominal pairs. see polypneustic.
peripodial cavities (ARTHRO: Insecta) A cavity formed during metamorphosis when the imaginal disc becomes invagi-nated beneath the larval epidermis.
peripodial membrane (ARTHRO: Insecta) The cell layer or wall surrounding the peripodal cavity and at pupation, comes to form part of the epidermis of the general body wall.
peripodial sac (ARTHRO: Insecta) In metamorphosis, the membrane enclosing the imaginal disc (bud).
periproct n. [Gr. peri, around; proktos, the anus] 1. The distal piece or segment of the body containing the anus. 2. (ANN: Oligochaeta) The pygomere or pygidium. 3. (ARTHRO) see telson. 4. (ECHINOD) The circular membrane containing the anus, surrounded by a varying number of embedded plates.
perisarc n. [Gr. peri, around; sarx, flesh] (CNID: Hydrozoa) A yellowish or brown chitinous covering of a colony that is secreted by the epidermis; the periderm.
perisomatic plates (ECHINOD: Crinoidea) Tegminal plates: interradials, interambulacrals, or radianal plates.
perispicular spongin (PORIF) Spongin surrounding spicules.
peristalsis n. [Gr. peri, around; stalsis, constriction] Rhythmic movement of the wall of the enteron or other tubular organs, traveling in successive contractions in one direction.
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