Animals with a coelom. The coelom develops from the mesoderm.
Amniotes
Animals whose young develop inside a fluid-filled sac, called an amnion.
Anthropoids
Primates that more resemble human form, like monkeys, apes, and humans.
Atrium
Entry chamber and name for the chambers of the heart where blood first enters.
Autotroph
Organism that can make its own food, like plants.
Bipedal
Moving around on two legs.
Biramous
Two branches splitting off from one, as in the legs of crustaceans.
Bilateral Symmetry
A shape where there are recognizable right and left, top and bottom and front and back. This is like an airplane.
Bilateria
The group of animals with bilateral symmetry.
Blastula
Hollow ball of cells the zygote becomes after going through cleavage.
Cephalization
Increasing 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.
Chordate
Animals with: a notochord, a hollow nerve cord, pharyngeal slits and a tail. This includes vertebrates.
Cilia
Long, 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.
Cladogram
A family tree showing the relationships between organisms.
Cleavage
The process of a zygote dividing into more cells.
Coelom
Internal space in an animal that forms in the embryo.
Coelomates
Animals without a coelom.
Deuterostomes
One 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.
Diapsid
Ancestral reptile whose name is based on its skull having two openings on either side of the head. Dinosaurs and modern reptiles descended from diapsids.
Diploblastic
An embryo with two ("diplo-") germ layers.
Diploid
Cell with two sets of chromosomes.
Ectotherms
Animals that get body heat from their surroundings.
Embryo
Multicellular early form of an organism in development.
Endotherms
Animals that can produce their own body heat.
Eukaryotes
Single-celled or multi-celled organisms whose cells have a nucleus and other organs enclosed by a membrane.
Eumetazoa
The other branch in the animal family tree. It means "true animals," those with all the characteristics of animals.
Eutherians
Mammals whose young complete their entire development internally in a placenta; also called placental mammals.
Evolution
The process of change organisms go through over time, leading to changes in organisms and to new organisms.
Exoskeleton
Hard structure on the outside of many invertebrates, for instance insects, spiders, and crustaceans, that provides support.
Flagella
Extension of a cell that looks like a little whip and can be used in movement or to move fluid
Fusiform
Body shape like a fish or dolphin, like a sleek, flattened tube with ends that come to a point.
Gametes
The single-celled reproductive cells that make a diploid organism. Sperm and eggs are gametes.
Ganglia
Bunch 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 Layers
The layers of the blastula. "Germ" means the beginning of something and each of these layers is the beginning of specific tissues.
Gestation
The process of an organism developing until birth.
Haploid
Cell with one set of chromosomes.
Hermaphrodite
Animal with both male and female reproductive organs.
Heterotroph
Organism that eats other organisms, like animals.
Hominids
Humans and human ancestors, characterized by being bipedal and having developed brains.
Hydrostatic Skeleton
Firm internal surface where muscles attach. This skeleton has no bones—the hard part is produced by internal water pressure.
Invertebrates
The group of animals without a backbone. This is the majority of animals.
Lateral Line System
Line of sensory organs down each side of a fish that can detect vibrations and changes in water pressure.
Malphigian Tubes
Tubes inside insects that take wastes to the outside.
Marsupials
Mammals that carry their young internally for only a short time, after which the rest of development happens in an external pouch.
Medusa
One 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.
Metamere
A segment of a worm. The metameres are like repeating units that line up to make up a whole organism.
Metamorphosis
Process 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.
Monotremes
Mammals characterized by not having a placenta and instead laying eggs.
Nephridia
Excretory 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.
Parapodia
Feet-like extensions on some annelids.
Parazoa
One 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.
Pheromones
Chemicals 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.
Placenta
An organ created along with the embryo. It connects the developing animal to the mother's bloodstream, providing food and oxygen.
Prokaryotes
Single-celled organisms without organs or a nucleus separated by membranes.
Prosimians
A group of tree-dwelling primates that least resemble humans, including lemurs, lorises, and tarsiers.
Protostomes
One 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).
Pseudocoelomates
Animals with a coelom that comes only partially from the mesoderm.
Radial Symmetry
A shape where all sides are the same, but there is a distinct top and bottom. This is like a pumpkin.
Radiata
The main branch of animals with radial symmetry.
Radula
Mouthpart in mollusks that is used for scraping food off surfaces.
Septa
Walls that divide the segments of an animal like a worm.
Sessile
An 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.
Setae
Bristles on the outside of some invertebrates like annelids (worms) and insects.
Tagmata
Distinct section of an arthropod body, usually with a unique purpose, for example the head.
Synapsid
Ancestral reptile who name is based on its skull having one opening on either side of the head. A synapsid was an ancestor of mammals.
Tetrapods
Animals with four limbs.
Therapsids
Descendants 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.
Trachea
A tube that carries air inside the body.
Triploblastic
An embryo with three ("triplo-") germ layers.
Ventricle
Chambers of the heart that receive blood from atria and send it out.
Vertebrate
Chordate animals that also have a skeletal spine made of parts called vertebrae.