Chapter 30: An Introduction to Animal Diversity

Deuterostomes

Deuterostomes

________ undergo radial cleavage, in which the early cell divisions are either parallel or at right angles to the polar axis, so the cells lie directly above or below one another.

Protostomes

________ undergo determinate cleavage, in which the fate of each embryonic cell is fixed very early.

Larvae

________ typically go through metamorphosis, a developmental process that converts the immature animal into a juvenile form that grows into an adult.

Molecular systematics

________ has confirmed much of animal phylogeny that was originally based on structural characters, including the axiom that animal body plans usually evolved from simple to complex.

Blastopore

In protostomes the ________, the opening from the embryonic gut to the outside, develops into the mouth.

freshwater

Because ________ is hypotonic to tissue fluid, animals must osmoregulate.

Lophotrochozoa

The ________ include the flatworms, ribbon worms, mollusks, annelids, rotifers, and animals that have a lophophore, a ciliated ring of tentacles surrounding the mouth.

Marine environments

________ have relatively stable temperatures, provide buoyancy, and provide readily available food.

Biologists

________ hypothesize that cnidarians (which have radial symmetry) and ctenophores (which have biradial symmetry) are more closely related to each other than to animals that exhibit bilateral symmetry.

Zygote

The ________ undergoes cleavage, a series of cell divisions that produce a hollow ball of cells called a blastula.

Embryonic tissues

________, called germ layers, include the outer layer, ectoderm, which gives rise to the body covering and the nervous system; the inner layer, endoderm, which lines the gut and other digestive organs; and a middle layer, mesoderm, which gives rise to muscle, skeletal structures, and most other body structures.

sexual reproduction sperm

In ________ and egg unite to form a zygote.

Terrestrial animals

________ must have adaptations that protect them from drying out and from temperature changes, and that protect their gametes and embryos.

Animals

________ are eukaryotic, multicellular, heterotrophic organisms with cells specialized to perform specific functions.

Body plan

The ________ is the basic structure and functional design of the body.

immature form

Most animals develop into a larva, a sexually ________ that may appear and behave differently from the adult.

Deuterostomes

________ undergo indeterminate cleavage, in which early in development each cell has the potential to develop into a complete organism.

Protostomes

________ undergo spiral cleavage, in which early cell divisions are diagonal to the polar axis.

Based on molecular data, biologists now subdivide the protostomes into two clades

Lophotrochozoa and Ecdysozoa