Term | Definition |
Invertebrate | Animal without a backbone; between 95-99 percent of animal species are invertebrates. |
Exoskeleton | Hard or tough outer covering of many invertebrates that provides support, protects body tissues, prevents water loss, and protects the organism from predation. |
Endoskeleton | INternal skeleton that protects internal organs, provides support for the organism's body, and can provide an internal brace for muscles to pull against. |
Vertebrate | Animal with an endoskeleton and a backbone. |
Hermaphrodite | Animal that produces both sperm and eggs in its body, generally at different times. |
Zygote | Fertilized egg formed when as sperm cell penetrates an egg. |
Internal Fertilization | Type of fertilization that occurs when sperm and egg combine inside an animal's body. |
External Fertilization | Type of fertilization that occurs when sperm and egg combine outside an animal's body. |
Blastula | Fluid-filled ball of cells formed by mitotic cell division of the embryo. |
Gastrula | Two-cell-layer sac with an opening at one end that forms from the blastula during embryonic development. |
Endoderm | Inner layer of cells in the gastrula that develops into digestive organs and the digestive tract lining. |
Ectoderm | Outer layer of cells in the gastrula that develops into nervous tissue and skin. |
Mesoderm | Layer of cells between the endoderm and the ectoderm that can become muscle tissue and tissue of the circulatory, respiratory, and excretory systems. |
Symmetry | Balance or similarity in body structures of organisms. |
Radial Symmetry | Body plan that can be divided along any plane, through a central axis, into roughly equal halves. |
Bilateral symmetry | Body plan that can be divided into mirror images along only one plane through the central axis. |
Anterior | Head end of an animal with bilateral symmetry. |
Cephalization | Tendency to concentrates sensory organs and nervous tissue at an animal's anterior end. |
Dorsal | Backside of an animal with bilateral symmetry. |
Ventral | Underside or belly of an animal with bilateral symmetry. |
Coelom | Fluid-filled body cavity completely surrounded by mesoderm. |
Pseudocoelom | Fluid-filled body cavity between the mesoderm and the endoderm. |
Acoelomate | Animal with a solid body that lacks a fluid-filled body cavity between the gut and the body wall. |
Prostosome | Coelomate animal whose mouth develops from the opening in the gastrula. |
Deuterostome | Coelomate animal whose anus develops from the opening in the gastrula. |
Filter Feeder | Organism that filters smalls particles from water to get its food. |
Sessile | Organism permanently attached to one place. |
Cnidocytes | Nematocyst-containing stinging cell on a cnidarian's tentacle. |
Nematocyst | Capsule whose threadlike tube contains poison and barbs and is discharged when prey touches a cnidarian. |
Gastrovascular Cavity | In cnidarians, the space surrounded by an inner cell, layer where digestion takes place. |
Nerve Net | Cnidarian nervous system that conducts impulses to and from all parts of the body. |
Polyp | Tube-shaped, sessile body form of cnidarians. |
Medusa | Umbrella-shaped, free swimming body form of cnidarians. |