Chapter 26
Terms
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- internal fertilization
- process in which eggs are fertilized inside the female's body
- nematocyst
- a poison-filled, stinging structure that contains a tightly coiled dart
- nerve net
- loosely organized network of nerve cells that together allow cnidarians to detect stimuli
- protostome
- an animal whose mouth is formed from the blastopore
- Cephalization
- concentration of sense organs and nerve cells at the front end of the body
- spicule
- spike-shaped structure made of chalklike calcium carbonate or glasslike silica
- osculum
- large hole at the top of the sponge
- vertebrates
- animals that have a backbone, or vertebral column
- bilateral symmetry
- body plan in which only a single, imaginary line can divide the body into two equal halves; characteristic of worms, arthropods, and chordates
- feedback inhibition
- process in which the product or result stops or limits the process
- Invertebrates
- animals that have no backbone, or vertebral column
- blastula
- hollow ball of cells formed when a zygote undergoes a series of divisions
- ectoderm
- outermost layer of most animals; gives rise to outer layer of skin, sense organs, and nerves
- endoderm
- innermost germ layer of most animals; develops into the linings of the digestive tract and much of the respiratory system
- cnidocyte
- stinging cell located along the tentacles of cnidarians; used for defense and to capture prey
- external fertilization
- process in which eggs are fertilized outside the female's body
- gastrovascular cavity
- a digestive chamber with one opening, in which cnidarians, flatworms, and echinoderms digest food
- hydrostatic skeleton
- layers of circular and longitudinal muscles, together with the water in the gastrovascular cavity, that enable movement
- archeaocytes
- specialized cells that move around within the walls of the sponge
- Choanocyte
- specialized cells that use flagella to move a steady current of water through the sponge
- polyp
- usually sessile stage of the life cycle of a cnidarian that has a cylindrical body with armlike tentacles
- larva
- an immature stage of an organism that looks different from the adult form
- medusa
- motile stage of the life cycle of a cnidarian that has a bell-shaped body
- mesoderm
- middle germ layer of most animals; gives rise to muscles and much of the circulatory, reproductive, and excretory system
- radial symmetry
- body plan in which body parts repeat around the center of the body; characteristics of sea anemones and sea stars
- deuterostome
- an animal whose anus is formed from the blastopore
- gemmule
- group of archaeocytes surrounded by a tough layer of spicules; produced by some sponges
- anus
- the opening through which wastes leave the digestive tract