Introduction to Animals Development, 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 Slide 2 of 23

Animal Development Following fertilization, animal embryos develop in a systematic fashion Slide 3 of 23

Animal Development Cleavage Gastrulation A series of rapid cell divisions No time for cells to grow in between divisions Gastrulation Formation of layers of tissue that eventually develop into body parts and organs Slide 4 of 23

Body Symmetry 3 different categories of body symmetry No symmetry (Asymmetrical) Ex. Sponges (Porifera) Radial symmetry Bilateral symmetry Slide 5 of 23

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) Some radially symmetrical animals are slightly modified so that they aren’t fully symmetrical on all planes. They tend to move slowly or not at all. (Purves, 621) Slide 6 of 23

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) Animals with bilateral symmetry also tend to move faster Slide 7 of 23

Directional Terms There are certain directional terms that can be associated with bilateral symmetry Dorsal = top side (think dorsal fin on dolphins) Ventral = bottom side Anterior = the end towards the head Posterior = the end towards the tail Slide 8 of 23

Embryonic Germ Layers Adult body parts develop from embryonic germ layers There are 3 different germ layers Ectoderm Mesoderm Endoderm Slide 9 of 23

Ectoderm Outermost layer Develops into skin, nervous system, sensory organs Slide 10 of 23

Mesoderm Middle layer Develops into muscles, bones, circulatory system, excretory system, most of reproductive system Not all animals have mesoderm Slide 11 of 23

Endoderm Inner most layer Develops into the digestive system, respiratory system Slide 12 of 23

Diplo or triplo? Not all animals have all 3 germ layers Diploblastic = only have 2 germ layers (no mesoderm, only endoderm and ectoderm) Ex. Cnidarians (jelly fish) Triploblastic = have all 3 germ layers All bilaterally symmetrical animals (worms, birds, mammals, etc) Closely linked to cephalization (concentration of nervous system and sensory organs close to head region) Slide 13 of 23

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 Slide 14 of 23

Types of Body Cavities Acoelomate Lack an enclosed body cavity Instead, the space is filled with cells Ex. Flatworm Slide 15 of 23

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 Slide 16 of 23

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 Slide 17 of 23

Protostomes vs. Deuterostomes Excluding sponges, cnidarians and ctenophores, all other animals can be classified as either a protostome or a deuterostome. Classification has to do with how the embryo develops. Early in development a cavity forms Blastopore = opening to the cavity Slide 18 of 23

Protostomes Blastopore becomes the mouth of the animal (means “mouth first” in Greek) Cleavage Spiral = cleavage occurs in planes diagonal to the vertical Determinate = The “fate” of each cell is determined very early Examples include: molluscs, annelids (earthworms), arthropods Slide 19 of 23

Deuterostomes Blastopore becomes the anus (means “mouth second” in Greek) Cleavage Radial = cleavage occurs along lines that are parallel or perpendicular to the vertical Indeterminate = the “fate” of each cell is not determined until a little later (early cells can still become any type of cell– “stem cells”) Examples include: Echinoderms, Chordates (have a backbone) Slide 20 of 23

Animal Classification 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 Slide 21 of 23

Animal Classification “Basal” animal = porifera (sponge) = simplest animal; at the bottom of the evolutionary tree Most animals have bilateral symmetry All animals are thought to belong to a group called Metazoa Slide 22 of 23

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