Introduction to Animals

Characteristics of Animals Heterotrophs Multicellular Eukaryotic Cells lack cell walls

Types of Animals Invertebrates Chordates More than 95% of all animal species At least 33 phyla Examples: sea stars, jellyfishes, worms, insects Chordates Fewer than 5% of all animal species Phylum Chordata Examples: fishes, amphibians, reptiles, birds and mammals

Phylum Chordata Have the following 4 characteristics during at least one stage of life Dorsal, hollow nerve cord Notochord Tail that extends beyond the anus Pharyngeal pouches

Dorsal, Hollow Nerve Cord Nerves branch from this cord at regular intervals Nerves connect to internal organs, muscles and sense organs

Notochord Long support rod Runs through the body just below the nerve cord Most chordates only have in the embryonic stage

Pharyngeal Pouches Paired structures in the throat (pharynx) region Fishes and amphibians: slits develop that connect the pharyngeal pouches to the outside of the body The slits may then develop into gills that are used for gas exchange

Post Anal Tail All chordates have a tail that extends beyond the anus at some point in their lives The tail can contain bone and muscles and is used in swimming by many aquatic species

What Animals Do to Survive Maintain Homeostasis Feedback Inhibition (Negative Feedback) Gather and Respond to Information Obtain and Distribute O2 & Nutrients Collect and Eliminate CO2 & Other Wastes Reproduce

Body Symmetry No Symmetry Radial Symmetry Bilateral Symmetry Animals have body parts extend from a central point Bilateral Symmetry Animals have distinct anterior and posterior ends and have right and left sides

Differentiation of Germ Layers Endoderm Innermost germ layer Develops into the linings of the digestive tract & much of the respiratory system Mesoderm Middle layer Develops into muscles & much of the circulatory, reproductive, & excretory systems Ectoderm Outermost layer Produces sense organs, nerves, & outer layer of the skin

Formation of a Body Cavity Acoelomates Invertebrates that lack a body cavity altogether Pseudocoelomates Invertebrates that have a body cavity only partially lined with mesoderm Coelomates Complex animal phyla that have a true body cavity (coelom) lined with mesoderm

Patterns of Embryological Development Zygote Fertilized egg Blastula Hollow ball of fells that develops when a zygote undergoes a series of cell divisions Protostome An animal whose mouth is formed from the blastopore Deuterostome Blastopore becomes an anus, and the mouth is formed from the second opening that develops

Segmentation Many bilaterally symmetrical animals develop into repeated parts Bilateral symmetry and segmentation are found together in many of the most successful animal groups Simple mutations can cause changes in the number of body segments Different segments can become specialized HOX GENES

Cephalization Getting a Head! Concentration of nerve cells at the anterior end of bilaterally symmetrical animals Examples: arthropods and vertebrates

Body Plans

The Cladogram of Animals Animal phyla are typically defined according to: Adult body plans Patterns of embryological development