Animal Evolution and Diversity
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ZygoteThe cell formed when sperm and egg first meet
AcoelomatesAnimals with a coelom. The coelom develops from the mesoderm.
AmniotesAnimals whose young develop inside a fluid-filled sac, called an amnion.
AnthropoidsPrimates that more resemble human form, like monkeys, apes, and humans.
AtriumEntry chamber and name for the chambers of the heart where blood first enters.
AutotrophOrganism that can make its own food, like plants.
BipedalMoving around on two legs.
BiramousTwo branches splitting off from one, as in the legs of crustaceans.
Bilateral SymmetryA shape where there are recognizable right and left, top and bottom and front and back. This is like an airplane.
BilateriaThe group of animals with bilateral symmetry.
BlastulaHollow ball of cells the zygote becomes after going through cleavage.
CephalizationIncreasing tendency to put all the sensory organs and a centralized nervous system at the front end of an organism. Certain branches of the animal tree go this direction.
ChordateAnimals with: a notochord, a hollow nerve cord, pharyngeal slits and a tail. This includes vertebrates.
CiliaLong, thin part of a cell that sticks outward and generally helps in movement. Similar to a flagella, but has a different structure and cilia are usually shorter and numerous, where flagella are longer and there are fewer to a cell.
CladogramA family tree showing the relationships between organisms.
CleavageThe process of a zygote dividing into more cells.
CoelomInternal space in an animal that forms in the embryo.
CoelomatesAnimals without a coelom.
DeuterostomesOne of two kinds of bilateria. Deuterostomes: 1) go through indeterminate cleavage; 2) have a blastopore that becomes the anus (versus mouth) and 3) form a coelom that remains part of the mesoderm.
DiapsidAncestral reptile whose name is based on its skull having two openings on either side of the head. Dinosaurs and modern reptiles descended from diapsids.
DiploblasticAn embryo with two ("diplo-") germ layers.
DiploidCell with two sets of chromosomes.
EctothermsAnimals that get body heat from their surroundings.
EmbryoMulticellular early form of an organism in development.
EndothermsAnimals that can produce their own body heat.
EukaryotesSingle-celled or multi-celled organisms whose cells have a nucleus and other organs enclosed by a membrane.
EumetazoaThe other branch in the animal family tree. It means "true animals," those with all the characteristics of animals.
EutheriansMammals whose young complete their entire development internally in a placenta; also called placental mammals.
EvolutionThe process of change organisms go through over time, leading to changes in organisms and to new organisms.
ExoskeletonHard structure on the outside of many invertebrates, for instance insects, spiders, and crustaceans, that provides support.
FlagellaExtension of a cell that looks like a little whip and can be used in movement or to move fluid
FusiformBody shape like a fish or dolphin, like a sleek, flattened tube with ends that come to a point.
GametesThe single-celled reproductive cells that make a diploid organism. Sperm and eggs are gametes.
GangliaBunch of nerve cells working together to control something gastrulation—process of the single layer of cells that makes up the blastula, dividing into multiple layers of cells.
Germ LayersThe layers of the blastula. "Germ" means the beginning of something and each of these layers is the beginning of specific tissues.
GestationThe process of an organism developing until birth.
HaploidCell with one set of chromosomes.
HermaphroditeAnimal with both male and female reproductive organs.
HeterotrophOrganism that eats other organisms, like animals.
HominidsHumans and human ancestors, characterized by being bipedal and having developed brains.
Hydrostatic SkeletonFirm internal surface where muscles attach. This skeleton has no bones—the hard part is produced by internal water pressure.
InvertebratesThe group of animals without a backbone. This is the majority of animals.
Lateral Line SystemLine of sensory organs down each side of a fish that can detect vibrations and changes in water pressure.
Malphigian TubesTubes inside insects that take wastes to the outside.
MarsupialsMammals that carry their young internally for only a short time, after which the rest of development happens in an external pouch.
MedusaOne form of the Cnidarians, which is like a floating sack with tentacles. The medusa is a reverse of the polyp, with tentacles pointing down. Medusas float freely.
MetamereA segment of a worm. The metameres are like repeating units that line up to make up a whole organism.
MetamorphosisProcess of changing from one form to another. This is part of the life cycle of some animals, for example frogs, which change from water-breathing tadpoles into air-breathing adult frogs.
MonotremesMammals characterized by not having a placenta and instead laying eggs.
NephridiaExcretory tube in earthworms and mollusks polyp—one form of the Cnidarians, which is shaped like a tube with tentacles pointing up. Polyps generally attach to something.
ParapodiaFeet-like extensions on some annelids.
ParazoaOne of the first two branches in the animal family tree. It means "sort-of an animal"—parazoa have most, but not all characteristics of animals.
PheromonesChemicals produced by an organism that cause a behavioral response in members of the same species.
Phylum (plural = Phyla)The second level of organization for all life. The first is kingdom.
PlacentaAn organ created along with the embryo. It connects the developing animal to the mother's bloodstream, providing food and oxygen.
ProkaryotesSingle-celled organisms without organs or a nucleus separated by membranes.
ProsimiansA group of tree-dwelling primates that least resemble humans, including lemurs, lorises, and tarsiers.
ProtostomesOne of the two kinds of bilateria. Protostomes: 1) go through determinate cleavage; 2) have a blastopore becomes the mouth (versus anus) and 3) form a coelom that splits off completely from the mesoderm (middle germ layer).
PseudocoelomatesAnimals with a coelom that comes only partially from the mesoderm.
Radial SymmetryA shape where all sides are the same, but there is a distinct top and bottom. This is like a pumpkin.
RadiataThe main branch of animals with radial symmetry.
RadulaMouthpart in mollusks that is used for scraping food off surfaces.
SeptaWalls that divide the segments of an animal like a worm.
SessileAn animal that doesn't move around. It may have tentacles or other parts that move, but the organism as a whole stays in one place.
SetaeBristles on the outside of some invertebrates like annelids (worms) and insects.
TagmataDistinct section of an arthropod body, usually with a unique purpose, for example the head.
SynapsidAncestral reptile who name is based on its skull having one opening on either side of the head. A synapsid was an ancestor of mammals.
TetrapodsAnimals with four limbs.
TherapsidsDescendants of the synapsids that led to mammals torsion—a special kind of development in snails where the embryo grow unevenly so the tail end finishes up above the head. The tail end makes the shell, which ends up on top.
TracheaA tube that carries air inside the body.
TriploblasticAn embryo with three ("triplo-") germ layers.
VentricleChambers of the heart that receive blood from atria and send it out.
VertebrateChordate animals that also have a skeletal spine made of parts called vertebrae.
ZygoteThe cell formed when sperm and egg first meet
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