| A | B |
|---|
| protist | diverse group of unicellular or multicellular eukaryotes that lack complex organ systems and live in moist environments |
| invertebrate | an animal without a backbone |
| exoskeleton | hard or tough outer covering that provides a framework of support, protects soft tissues, prevents water loss, and provides protection from predators |
| endoskeleton | internal skeleton |
| vertebrate | an animal that has an endoskeleton and a backbone |
| hermaphrodite | animals that produce both eggs and sperm in the same animal body |
| zygote | fertilized egg formed when a 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 system |
