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  Section: Zoological Terms used in General Zoology
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S - Zoological Terms

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(L. sacculus, small bag). Small chamber of the membranous labyrinth of the inner ear.


Adj. sacral (L. sacer, sacred). Bone formed by fused vertebrae to which pelvic girdle is attached; pertaining to the sacrum.


(L. sagitta, arrow). Pertaining to the median anteroposterior plane that divides a bilaterally symmetrical organism into right and left halves.


(L. sal, salt). The reaction product of an acid and a base; dissociates in water solution to negative and positive ions, but not H+ or OH-.


(Gr. sapros, rotten, + phagos, from phagein, to eat). Feeding on decaying matter; saprobic; saprozoic.


(Gr. sapros, rotten, + phyton, plant). A plant living on dead or decaying organic matter.

saprozoic nutrition

(Gr. sapros, rotten, + zoon, animal). Animal nutrition by absorption of dissolved salts and simple organic nutrients from surrounding medium; also refers to feeding on decaying matter.


(Gr. sarx, flesh, + lemma, rind). The thin, noncellular sheath that encloses a striated muscle fiber.


(Gr. sarx, flesh, + meros, part). Transverse segment of striated muscle believed to be the fundamental contractile unit.


(Gr. sarx, flesh, + plasma, mold). The clear, semifluid cytoplasm between the fibrils of muscle fibers.


(Gr. sauros, lizard, + pteryginos, winged). Mesozoic marine reptiles.


(Gr. schizo, from schizein, to split, + koiloma, cavity). A coelom formed by the splitting of embryonic mesoderm. Noun, schizocoelomate, an animal with a schizocoel, such as an arthropod or mollusc. Adj., schizocoelous

schizocoelous mesoderm formation

Embryonic formation of the mesoderm as cords of cells between ectoderm and endoderm; splitting of these cords results in the coelomic space.


(Gr. schizein, to split, + gonos, seed). Multiple asexual fission.


(skler´it) (Gr. skleros, hard). A hard chitinous or calcareous plate or spicule; one of the plates making up the exoskeleton of arthropods, especially insects.


(Gr. skleros, hard, + blastos, germ). An amebocyte specialized to secrete a spicule, found in sponges.


(Gr. skleros, hard, + kytos, hollow vessel). An amebocyte in sponges that secretes spicules.


(Gr. skleros, hard). Pertaining to the tough outer coat of the eyeball.


Process of hardening of the cuticle of arthropods by the formation of stabilizing cross linkages between peptide chains of adjacent protein molecules.


(Gr. skolex, worm, grub). The holdfast, or so-called head, of a tapeworm; bears suckers and, in some, hooks, and posterior to it new proglottids are differentiated.


(L. bag). The pouch that contains the testes in most mammals.


(Gr. skyphos, cup, + stoma, mouth). A stage in the development of scyphozoan jellyfish just after the larva becomes attached, the polyp form of a scyphozoan.


(L. sebaceus, made of tallow). A type of mammalian epidermal gland that produces a fatty substance.


Stationary, sitting, inactive; staying in one place.

selectively permeable

Permeable to small particles, such as water and certain inorganic ions, but not to larger molecules.


(L. semen, semen, + ferre, to bear). Pertains to the tubules that produce or carry semen in the testes.


(L. semi, half, + permeabilis, capable of being passed through). Permeable to small particles, such as water and certain inorganic ions, but not to larger molecules.


pl. sensilla (L. sensus, sense). A small sense organ, especially in the arthropods.


pl. septa (L. fence). A wall between two cavities.

serial homology

See homology


(N.L. from L. serum, serum). The outer embryonic membrane of birds and reptiles; chorion. Also, the peritoneal lining of the body cavity.


(L. serum, serum). A phenolic amine, found in the serum of clotted blood and in many other tissues, that possesses several poorly understood metabolic, vascular, and neural functions; 5-hydroxytryptamine.


(L. serum, serum). Watery, resembling serum; applied to glands, tissue, cells, fluid.


(L. whey, serum). The liquid that separates from the blood after coagulation; blood plasma from which fibrinogen has been removed. Also, the clear portion of a biological fluid separated from its particulate elements.


(L. sessilis, low, dwarf). Attached at the base; fixed to one spot, not able to move about.


pl. setae (se´te) (L. bristle). A needlelike chitinous structure of the integument of annelids, arthropods, and others.

sex chromosomes

Chromosomes that determine gender of an animal. They may bear a few or many other genes.

sibling species

Reproductively isolated species that are so similar morphologically that they are difficult or impossible to distinguish using morphological characters.

sickle cell anemia

A condition that causes the red blood cells to collapse (sickle) under oxygen stress. The condition becomes manifest when an individual is homozygous for the gene for hemoglobin-S (HbS).


(L. silex, flint). Containing silica.


(L. simia, ape). Pertaining to monkeys or apes.


(L. sinister, left). Pertaining to the left; in gastropods, shell is sinistral if opening is to left of columella when held with spire up and facing observer.


(L. curve). A cavity or space in tissues or in bone.


(Gr. siphon, reed, tube, siphon, + glyphe, carving). Ciliated furrow in the gullet of sea anemones.


(L. siphunculus, small tube). Cord of tissue running through the shell of a nautiloid, connecting all chambers with body of animal.

sister group

The relationship between a pair of species or higher taxa that are each other's closest phylogenetic relatives.


Ethological study of social behavior in humans or other animals.


(Gr. solen, pipe). Channels through the coenenchyme connecting the polyps in an alcyonarian colony (phylum Cnidaria).


(Gr. solen, pipe, + kytos, hollow vessel). Special type of flame bulb in which the bulb bears a flagellum instead of a tuft of flagella. See flame cell, protonephridium


(Gr. body). The whole of an organism except the germ cells (germ plasm).


(Gr. soma, body). Refers to the body, for example, somatic cells in contrast to germ cells.


(Gr. soma, the body, + koilos, hollow). Posterior coelomic compartment of echinoderms; left somatocoel gives rise to oral coelom, and right somatocoel becomes aboral coelom.


(Gr. soma, body, + plasma, anything formed). The living matter that makes up the mass of the body as distinguished from germ plasm, which makes up the reproductive cells. The protoplasm of body cells.


(Gr. soma, body). One of the blocklike masses of mesoderm arranged segmentally (metamerically) in a longitudinal series beside the neural tube of the embryo; metamere.


Differential survival and reproduction among varying individuals; often confused with natural selection which is one possible cause of sorting.


(L. species, kind). The evolutionary process or event by which new species arise.


sing. and pl. (L. particular kind). A group of interbreeding individuals of common ancestry that are reproductively isolated from all other such groups; a taxonomic unit ranking below a genus and designated by a binomen consisting of its genus and the species name.


(Gr. sperma, seed, + theke, case). A sac in the female reproductive organs for the reception and storage of sperm.


(Gr. sperma, seed, + eidos, form). A growth stage of a male reproductive cell arising by division of a secondary spermatocyte; gives rise to a spermatozoon.


(Gr. sperma, seed, + kytos, hollow vessel). A growth stage of a male reproductive cell; gives rise to a spermatid.


(Gr. sperma, seed, + genesis, origin). Formation and maturation of spermatozoa.


(Gr. sperma, seed, + gone, offspring). Precursor of mature male reproductive cell; gives rise directly to a spermatocyte.


(Gr. sperma, spermatos, seed, + pherein, to bear). Capsule or packet enclosing sperm, produced by males of several invertebrate groups and a few vertebrates.


(Gr. sphinkter, band, sphincter, from sphingein, to bind tight). A ring-shaped muscle capable of closing a tubular opening by constriction.


(L. dim. spica, point). One of the minute calcareous or siliceous skeletal bodies found in sponges, radiolarians, soft corals, and sea cucumbers.


(L. spiraculum, from spirare, to breathe). External opening of a trachea in arthropods. One of a pair of openings on the head of elasmobranchs for passage of water. Exhalent aperture of tadpole gill chamber.

spiral cleavage

A type of embryonic cleavage in which cleavage planes are diagonal to the polar axis and unequal cells are produced by the alternate clockwise and counterclockwise cleavage around the axis of polarity; determinate cleavage.


(L. spongia, sponge). Fibrous, collagenous material making up the skeletal network of horny sponges.


(Gr. spongos, sponge, ´ blastos, bud). Cell in a sponge that secretes spongin, a protein.


(Gr. spongos, sponge, + koilos, hollow). Central cavity in sponges.


(Gr. spongos, sponge, + kytos, hollow vessel). A cell in sponges that secretes spongin.


(Gr. sporos, seed, + kystis, pouch). A larval stage in the life cycle of flukes; it originates from a miracidium.


(Gr. sporos, seed, + gonos, birth). Multiple fission to produce sporozoites after zygote formation.


(Gr. sporos, seed, + zoon, animal, + ite, suffix for body part). A stage in the life history of many sporozoan protozoa; released from oocysts.


(L. squalus, a kind of fish). A liquid acyclic triterpene hydrocarbon found especially in the liver oil of sharks.

squamous epithelium

(L. squama, scale, + osus, full of). Simple epithelium of flat, nucleated cells.


(L. stirrup). Stirrup-shaped innermost bone of the middle ear.


(Gr. statos, standing, fixed, + blastos, germ). Biconvex capsule containing germinative cells and produced by most freshwater ectoprocts by asexual budding. Under favorable conditions it germinates to give rise to new zooid.


(Gr. statos, standing,+ kystis, bladder). Sense organ of equilibrium; a fluid-filled cellular cyst containing one or more granules (statoliths) used to sense direction of gravity.


(Gr. statos, standing, + lithos, stone). Small calcareous body resting on tufts of cilia in the statocyst.


(Gr. stenos, narrow, + hals, salt). Pertaining to aquatic organisms that have restricted tolerance to changes in environmental saltwater concentration.


(Gr. stenos, narrow, + phagein, to eat). Eating few kinds of foods.


(Gr. stenos, narrow, + topos, place). Refers to an organism with a narrow range of adaptability to environmental change; having a restricted environmental distribution.


(Gr. stereos, solid, + gaster, stomach, + L. ula, dim.). A solid type of gastrula, such as the planula of cnidarians.


(Gr. stereos, solid, hard, firm). Meshwork structure of endoskeletal ossicles of echinoderms.

stereotyped behavior

A pattern of behavior repeated with little variation in performance.


(L. breastbone). Ventral plate of an arthropod body segment; breastbone of vertebrates.


steroid (ste´roid) (Gr. stereos, solid, + L. ol, from oleum, oil). One of a class of organic compounds containing a molecular skeleton of four fused carbon rings; it includes cholesterol, sex hormones, adrenocortical hormones, and vitamin D.


(Gr. stigma, mark, tatoo mark). Eyespot in certain protozoa. Spiracle of certain terrestrial arthropods.


(L. stolo, stolonis, a shoot, or sucker of a plant). A rootlike extension of the body wall giving rise to buds that may develop into new zooids, thus forming a compound animal in which the zooids remain united by the stolon. Found in some colonial anthozoans, hydrozoans, ectoprocts, and ascidians.


(Gr. mouth). A mouthlike opening.


(Gr. stoma, mouth, + chorde, cord). Anterior evagination of the dorsal wall of the buccal cavity into the proboscis of hemichordates; the buccal diverticulum.


(Gr. strobile, lint plug like a pine cone [strobilos]). A stage in the development of the scyphozoan jellyfish. Also, the chain of proglottids of a tapeworm.


(Gr. strobilos, a pine cone). Repeated, linear budding of individuals, as in scyphozoans (phylum Cnidaria), or sets of reproductive organs, as in tapeworms (phylum Platyhelminthes).


(Gr. stroma, bedding). Supporting connective tissue framework of an animal organ; filmy framework of red blood corpuscles and certain cells.

structural gene

A gene carrying the information to construct a protein.


(L. sub, under, below, + nivis, snow). Applied to environments beneath snow, in which snow insulates against a colder atmospheric temperature.


The substance upon which an enzyme acts; also, a base or foundation (substratum); and the substance or base on which an organism grows.


(Gr. sykon, fig). A type of canal system in certain sponges. Sometimes called syconoid.


(Gr. syn, with, + bios, life). The living together of two different species in an intimate relationship. Symbiont always benefits; host may benefit, may be unaffected, or may be harmed (mutualism, commensalism, and parasitism).


(Gr. syn, with, + patra, native land). Having the same or overlapping regions of geographical distribution. Noun,



Sharing among species of ancestral characteristics, not indicative that the species comprise a monophyletic group.


(Gr. syn, together with, + apo, of, + morphe, form). Shared, evolutionarily derived character states that are used to recover patterns of common descent among two or more species.


(Gr. synapsis, contact, union). The place at which a nerve impulse passes between neuron processes, typically from an axon of one nerve cell to a dendrite of another nerve cell.


(Gr. synapsis, contact, union). An amniote lineage comprising the mammals and the ancestral mammal-like reptiles, having a skull with a single pair of temporal openings.


(Gr. synapsis, contact, union). The time when the pairs of homologous chromosomes lie alongside each other in the first meiotic division.

synaptonemal complex

(Gr. synapsis, a joining together, ´ nema, thread). The structure that holds homologous chromosomes together during synapsis in prophase of meiosis I.


adj. syncytial (Gr. syn, with, + kytos, hollow). A multinucleated cell.


(Gr. syn, with, + dramein, to run). A group of symptoms characteristic of a particular disease or abnormality.


(Gr. syn, with, + gamos, marriage). Fertilization of one gamete with another individual gamete to form a zygote, found in most animals with sexual reproduction.


(Gr. syn, with, + karyon, nucleus). Zygote nucleus resulting from fusion of pronuclei.


(Gr. shepherd's pipe). The vocal organ of birds located at the base of the trachea.


Science of classification and reconstruction of phylogeny.


(Gr. systole, drawing together). Contraction of heart.

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