Sigmoid curve see logistic curve

signa; sing. signum [L. signum, sign] (ARTHRO: Insecta) In female Lepidoptera, spines or dentate or roughened patches on the inner wall of the corpus bursae, thought to function in holding or breaking up spermatophores.

silicalemma n. [L. silex, flint; Gr. lemma, peel] (PORIF) A unit membrane enclosing the axial filament of a siliceous spi-cule.

siliceous, silicious a. [L. silex, flint] Of or pertaining to silica.

silicoblasts [L. silex, flint; Gr. blastos, bud] (PORIF) A cell that secretes all or part of a siliceous spicule.

siliquiform a. [L. siliqua, a pod; forma, shape] Having the shape of a silique; long, tubular and narrow like a pod.

silk n. [Gr. serikos, silk] 1. A secretion that hardens so rapidly on extrusion that it may be produced as a long continuous thread. 2. (ARTHRO: Chelicerata) Secreted by specialized salivary glands in Acari; anterior of the abdomen in Ara-neae; the galea of Pseudoscorpionida. 3. (ARTHRO: Insecta) Secreted from dermal openings on the abdomen in some Coleoptera; foretarsi in Embioptera and some empidid Diptera; malpighian tubes discharging at the anus in Neu-roptera, some Coleoptera and Hymenoptera; mouth cavity (usually modified salivary glands) in Psocoptera, Sipho-naptera, some Diptera, Trichoptera, Lepidoptera and Hymenoptera.

silk glands Glands that secrete the liquids that produce silk on exposure to the air.

silk press (ARTHRO: Insecta) In Lepidoptera larvae, a structure similar to a typical salivary pump in which the silk is molded to a thread; silk regulator; thread press.

silvicolous a. [L. silva, forest; colere, to dwell] Inhabiting or growing in forests or woodlands.

simple a. [L. simplex, simple] Without embellishment; not modified, forked, toothed, branched or divided.

simple eyes (ARTHRO: Insecta) The ocelli.

simple seta see unjointed seta simple skeletal wall (BRYO: Stenolaemata) Having the wall calcified only on edges and one side.

simple velum (ARTHRO: Crustacea) In Ostracoda, a velate structure of flange- or ridgelike form.

simple-walled colony see fixed-walled colony sinciput n. [L. semi-, half; caput, head] 1. Upper or forepart of the head. 2. (ARTHRO: Insecta) The head area between the vertex and clypeus, especially in Coleoptera.

single band of crochets see mesoseries single-walled colony see fixed-walled colony sinistral a. [L. sinistra, left] Pertaining to the left; to the left of the median line.

sinistral gastropods (MOLL) Having the genitalia on the left side of the head-foot mass or pallial cavity, and commonly the shell, when viewed with the apex uppermost, with the aperture on the left. see dextral gastropods.

sinistron n. [L. sinistra, left] The left side of the body.

sinistrorse a. [L. sinistra, left; vertere, to turn] An organism spirally twisting to the left. see dextrorse.

sinuate a. [L. sinus, curve] Wavy; tortuous; curving in and out.

sinuatolobate a. [L. sinus, curve; Gr. lobos, lobe] Sinuate and lobed.

sinuosity a. [L. sinus, curve] Series of curves or bends.

sinupalliate a. [L. sinus, curve; pallium, mantle] (MOLL: Bival-via) Having a pallial sinus or recess in the posterior part of the pallial impression due to the retraction of the siphons.

sinus n. [L. sinus, curve] A depression; bend; embayment.

sinus gland (ARTHRO: Crustacea) Storage release site for neurosecretory material synthesized within the cell bodies containing hormones produced by x-organ and other sites of the central nervous system.

siphon n. [Gr. siphon, tube] Any tubular or siphon-like struc ture. siphonal a.

siphonal area (MOLL: Bivalvia) The posterior sector of the shell surface, usually demarcated anteriorly by the umbonal ridge; secreted at the openings in the mantle edge or elevated to form siphons.

siphonal canal (MOLL: Gastropoda) A tubular or troughlike extension of the aperture for the enclosure of the siphon.

siphonal fasciole (MOLL: Gastropoda) The curved growth lines near the foot of the columella marking successive positions of the siphonal notch.

siphonal fold (MOLL: Gastropoda) A ridge corresponding to the siphonal notch that winds spirally around the columella.

siphonal notch (MOLL: Gastropoda) A narrow sinus of the ap-ertural margin near the base of the columella functioning for protrusion of the inhalant siphon.

siphonal retractor muscles (MOLL: Bivalvia) Muscles that retract siphons into the shell.

siphonal tube (MOLL: Bivalvia) A tube composed of aggluti-nized particles derived from boring and fused to the si-phonoplax. see chimney.

siphonoglyph n. [Gr. siphon, tube; glyphein, to engrave] (CNID: Anthozoa) A special groove or canal from the mouth to the actinopharynx, functioning to circulate fluid through the coelenteron.

siphonoplax n. [Gr. siphon, tube; plax, plate] (MOLL: Bivalvia) A chitinous or calcareous structure secreted by the mantle diverging or fused to form a tube on the posterior margin of the valves; probably for protection of the siphons.

siphonostomatous a. [Gr. siphon, tube; stoma, mouth] (MOLL: Gastropoda) Having the apertural margin notched or formed with a canal for the protrusion of the siphon.

siphonozooid n. [Gr. siphon, tube; zoon, animal; eidos, form] (CNID: Anthozoa) A small, modified polyp with reduced or lacking tentacles, having a well developed siphonoglyph to propel water through the canal system of the colony.

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