Insects and crustaceans have a skeleton different from ours. Theirs is an ____________: a skeleton that forms an ____________ on an animal body.

Animals with an exoskeleton are able to continue to grow by employing the practice of ____________, which can be defined as____________.

With respect to egg fertilization and protection, the primitive, ancestral state in the animal kingdom is believed to be one in which eggs and sperm are _________ into water and brought together by water currents, after which parents provide ________ care to fertilized eggs.

The more complex the animal in the animal kingdom, the ________ the number of eggs that are likely to be produced and the _________ amount of care parents are likely to provide to fertilized eggs.

The amniotic egg, which evolved in ________, was important because it allowed eggs to be laid ________.

Sexual reproduction in animals entails a fusion of ____________ and ____________ from different individuals.

Budding, fission, and parthenogenesis are all forms of _________ practiced by animals. In parthenogenesis, an ____________ develops into an adult organism.

An animal that possesses both male and female sex organs is known as a ________.

Sponges obtain nutrition and oxygen, and get rid of wastes, by ________through themselves.

The three most familiar classes of molluscs are the gastropods, one example of which is ; the bivalves, one example of which is ________; and the cephalopods, one example of which is ________.

Cnidarians tend to exhibit both a mobile ________ stage in which their mouths are on ________ of their bodies, and a sessile ________ stage, in which their mouths are