Chapter 25 What is an Animal ? -Biology

Mesoderm

- musculoskeletal system, circulatory system, excretory system, gonads, connective tissue throughout the body and portions of digestive and respiratory organs

Blastula

A hollow ball of cells that marks the end of the cleavage stage during early embryonic development in animals. B

Deuterostomes

A major lineage of animals that share a pattern of embryological development, including radial cleavage, formation of the anus earlier than the mouth, and formation of the coelom by pinching off of layers of mesoderm from the gut. Includes echinoderms and chordates. Compare with protostome.

Protostome

A member of one of two distinct evolutionary lines of coelomates, consisting of the annelids, mollusks, and arthropods, and characterized by spiral, determinate cleavage, schizocoelous formation of the coelom, and development of the mouth from the blastopore.

Acoelomate

A solid-bodied animal lacking a cavity between the gut and outer body wall.

invertebrate

An animal that does not have a backbone.

vertebrate

An animal with a backbone

Exoskeleton

An external skeleton.

Endoskeleton

An internal skeleton

ventral

At the belly side of the human body D

Posterior

Back of the body C

Dorsal

Being or located near, on, or toward the back or posterior part of the human body B

Bilateral Symmetry

Body plan in which only a single, imaginary line can divide the body into two equal halves.

sessile

Describes an organism that remains attached to a surface for its entire life and does not move

Gastrula

During the second week, the two layer bilaminar embryo becomes a three layer embro, what is this process called? C

Endoderm

Forms epithelial linings of the digestive, respiratory, and urogenital systems

Anterior

Front of body A

Ectoderm

One of the three primary (embryonic) germ layers formed during gastrulation. Ectoderm ultimately forms external structures such as the skin, hair, nails, and inner linings of the mouth and anus, as well as the entire nervous system.

coelm

a body cavity that lies between the gut and body wall. It has a lining, the peritoneum, which is derived from mesoderm. It develops differently in the embryos of protostomes and deuterostomes

radial symmetry

body plan in which body parts repeat around the center of the body; characteristic of sea anemones and sea stars

psueudocoelom

fluid-filled body cavity between the mesoderm and the endoderm