(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
(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-.
rotten, + phagos, from phagein, to eat).
Feeding on decaying matter; saprobic;
(Gr. sapros, rotten, + phyton, plant). A plant living on dead or
decaying organic matter.
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
(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.
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
(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
hardening of the cuticle of arthropods by
the formation of stabilizing cross linkages
between peptide chains of adjacent protein
(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
(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.
inactive; staying in one place.
Permeable to small
particles, such as water and certain
inorganic ions, but not to larger molecules.
semen, + ferre, to bear). Pertains to the
tubules that produce or carry semen in the
(L. semi, half, + permeabilis,
capable of being passed through).
Permeable to small particles, such as water
and certain inorganic ions, but not to larger
pl. sensilla (L. sensus,
sense). A small sense organ, especially in
pl. septa (L. fence). A wall between
(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;
(L. serum, serum). Watery,
resembling serum; applied to glands, tissue,
(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
determine gender of an animal. They may
bear a few or many other genes.
species that are so similar morphologically
that they are difficult or impossible
to distinguish using morphological
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
(L. simia, ape). Pertaining
to monkeys or apes.
left). Pertaining to the left; in gastropods,
shell is sinistral if opening is to left of
columella when held with spire up and
(L. curve). A cavity or space in
tissues or in bone.
reed, tube, siphon, + glyphe, carving).
Ciliated furrow in the gullet of sea
(L. siphunculus, small
tube). Cord of tissue running through the
shell of a nautiloid, connecting all chambers
with body of animal.
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
(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
(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.
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.
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
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.
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
(L. spongia, sponge).
Fibrous, collagenous material making up the
skeletal network of horny sponges.
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.
(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.
narrow, + hals, salt). Pertaining to aquatic
organisms that have restricted tolerance to
changes in environmental saltwater
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
solid, + gaster, stomach, + L. ula, dim.). A
solid type of gastrula, such as the planula of
(Gr. stereos, solid, hard,
firm). Meshwork structure of endoskeletal
ossicles of echinoderms.
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
(Gr. stigma, mark, tatoo mark). Eyespot
in certain protozoa. Spiracle of certain
(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
(Gr. stoma, mouth, + chorde, cord). Anterior evagination of the
dorsal wall of the buccal cavity into the
proboscis of hemichordates; the buccal
(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
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.
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
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
(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
(Gr. syn, with, + patra, native land). Having the same or
overlapping regions of geographical
Sharing among species of ancestral
characteristics, not indicative that the
species comprise a monophyletic group.
together with, + apo, of, + morphe, form).
Shared, evolutionarily derived character
states that are used to recover patterns of
common descent among two or more
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
(Gr. synapsis, contact,
union). An amniote lineage comprising the
mammals and the ancestral mammal-like reptiles, having a skull with a single pair of
(Gr. synapsis, contact,
union). The time when the pairs of
homologous chromosomes lie alongside
each other in the first meiotic division.
(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
(Gr. syn, with, + dramein, to run). A group of symptoms
characteristic of a particular disease or
(Gr. syn, with, + gamos, marriage). Fertilization of one
gamete with another individual gamete to
form a zygote, found in most animals with
(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
classification and reconstruction of
(Gr. systole, drawing
together). Contraction of heart.