Introduction to Animals Symmetry, Tissues, Classification AP Biology Unit 6

Defining Characteristics of Animals Multicellular Heterotrophs Sexual reproduction followed by development of body tissues and organs from layers of embryonic tissue

Body Symmetry 3 different categories of body symmetry –No symmetry (Asymmetrical) Ex. Sponges (Porifera) –Radial symmetry –Bilateral symmetry Picture taken withour permission from Porifera/Images/Amphimedon.jpg

Radial Symmetry One main axis in the center No left or right sides– dividing the animal along any axis makes it a mirror image on each side. Ex. Sea Anemones, Cnidarians (jellyfish)

Bilateral Symmetry Has a left and right side– only one plane will divide the animal so that the two sides are mirror images of one another. Ex. Humans, fish, insects (most animals have bilateral symmetry)

Embryonic Germ Layers Adult body parts develop from embryonic germ layers There are 3 different germ layers –Ectoderm –Mesoderm –Endoderm Having a 3 layers closely linked to cephalization (concentration of nervous system and sensory organs close to head region)

Ectoderm Outermost layer Develops into skin, nervous system, sensory organs

Mesoderm Middle layer Develops into muscles, bones, circulatory system, excretory system, most of reproductive system Not all animals have mesoderm

Endoderm Inner most layer Develops into the digestive system, respiratory system

Body Cavities Most animals have a body cavity (fluid filled space) between the endoderm and ectoderm Coelom = body cavity lined with mesoderm Type of body cavity influences how the animal moves

Types of Body Cavities Acoelomate –Lack an enclosed body cavity –Instead, the space is filled with cells –Ex. Flatworm

Types of Body Cavities Pseudocoelomate –Have a fluid filled space in which many organs are suspended –Only one side (outer side) is lined with mesoderm (muscle) –Can’t control body shape as well since only one layer of muscle –Ex. Roundworm

Types of Body Cavities Coelomate –Have a coelom – body cavity lined with mesoderm on both sides –Better control over movement since there are more muscles present (usually going in several different directions) –Ex. Earthworm, humans

Animal Classification Originally based on developmental morphology Molecular evidence suggests that this classification may not be entirely accurate Common ancestor of all animals is thought to be a colonial protist with a flagella

Animal Classification porifera (sponge) = simplest animal; at the bottom of the evolutionary tree Most animals have bilateral symmetry

Scientific Names for Animals Porifera = sponges Cnidarians = jellyfish Platyhelminthes = flatworms Nematodes = roundworms Annelids = Earthworms Arthropods = insects, crustaceans Echinoderms = starfish Chordates = (have a backbone) humans, birds, fish, amphibians Slide 23 of 23