Introduction to Animals Chapter 25 Introduction to Animals

Section 1 What is an Animal?

Characteristics of Animals All animals are MULTICELLULAR, HETEROTROPHIC, and EUKARYOTIC. Their cells lack CELL WALLS.

Types of Animals INVERTEBRATES do not have a backbone, or VERTEBRAL column. More than 95 percent of all animal species are invertebrates. Invertebrates are classified in at least 33 phyla, the largest taxonomic groups of animals. Examples of invertebrates are SEA STARS, JELLYFISHES, and INSECTS.

Types of Animals CHORDATES exhibit four characteristics during some stage of development: a dorsal, hollow NERVE CORD; and NOTOCHORD; and TAIL that extends beyond the anus; and PHARYNGEAL pouches.

Types of Animals A NOTOCHORD is a supporting rod that runs through the body just below the NERVE CORD. PHARYNGEAL POUCHES are paired structures in the throat region. Most chordates develop a backbone, or vertebral column. They are VERTEBRATES.

What Animals Do to Survive Animals must maintain HOMEOSTASIS in order to survive. One important way to maintain homeostasis is FEEDBACK INHIBITION, also called negative feedback, in which the product or result of one process limits the process itself.

What Animals Do to Survive In order to maintain homeostasis, animals must: GATHER and respond to information; OBTAIN and distribute OXYGEN and NUTRIENTS; COLLECT and eliminate carbon dioxide and collect wastes. They also REPRODUCE.

Animal Body Plans and Evolution Section 2 Animal Body Plans and Evolution

Features of Body Plans Each animal phylum has a unique organization of body structures called its “BODY PLAN”. The features of a body plan include Levels of organization: CELLS, TISSUES, ORGANS, ORGAN SYSTEMS

Features of Body Plans Body symmetry RADIAL symmetry: body parts extend from CENTRAL POINT BILATERAL symmetry: left and right sides are MIRROR IMAGES, with front and back ends

Features of Body Plans Differentiation of germ layers: ENDODERM, the innermost layer MESODERM, the middle layer ECTODERM, the outermost layer

Features of Body Plans Formation of cavity, or FLUID-FILLED space between the digestive tract and the body wall: A true COELOM (found in most complex animal phyla) develops in the MESODERM and is lined with tissue derived from the MESODERM

Features of Body Plans A PSEUDOCOELOM is only partially lined with MESODERM

Features of Body Plans Some invertebrates lack a body cavity and some only have a primitive, JELLYLIKE layer between ECTODERM and ENDODERM.

Features of Body Plans Patterns of embryological development Sexual reproducing animals begin life as a ZYGOTE, or fertilized egg The zygote develops into a hollow ball of cells, the BLASTULA.

Features of Body Plans The blastula folds in on itself and creates a tube that becomes the DIGESTIVE TRACT; the tube has a single opening, the BLASTOPORE: In PROTOSTOMES (most invertebrates), the blastopore becomes the mouth In DEUTEROSTOMES (chordates and echinoderms), the blastopore becomes the anus.

Features of Body Plans SEGMENTATION: repeated parts, such as the segments of worms CEPHALIZATION: the concentration of sense organs and nerves near the anterior (HEAD) end LIMB formation: external appendages such as LEGS, FLIPPERS, and WINGS

The Cladogram of Animals The features of body plants provide the evidence needed to build a CLADOGRAM, or phylogenetic tree, of all animals. Animal phyla are usually defined by their adult body plans and patterns of embryological development.

The Cladogram of Animals The characteristics of animals VARY within each phylum. Each phylum may be thought of as an “EVOLUTIONARY EXPERIMENT.” Phyla with successful body plans have survived.