What is an Animal? Eukaryotes Multicellular Heterotrophs Have ways to move, reproduce, obtain food, protect themselves; lots of kinds of specialized cells

Characteristics of Animals Methods of obtaining food –Grazers/Gatherers/Hunters – must move about to get food –Filter feeders – are sessile, meaning they don’t move from place to place Must digest food –Wide variety in digestive tracts Specialized cells –Different cells carry out different functions, all within one organism

Development of Animals Most animals reproduce sexually –Fertilization Occurs when sperm penetrates egg, forming a unicellular zygote –Cleavage Occurs when the zygote divides forming two new cells Organism is called an embryo once cell division has begun –Blastula Formation A hollow ball of cells called a blastula forms as cell division proceeds –Gastrula Formation Cells on one side of the blastula fold inward, forming a gastrula Gastrula - a structure made up of two layers of cells, with an opening at one end »Ectoderm – the outside cell layer of the gastrula »Endoderm – the inside cell layer of the gastrula

Development of Animals Fertilization Cleavage Gastrula Formation

Development of Animals Mesoderm –Mesoderm – a third cell layer found between the ectoderm and the endoderm, not present in all animals Continued growth and development –Protostomes – animals in which the opening in the gastrula becomes the mouth –Deuterostomes – animals in which the opening in the gastrula becomes the anus –As cell division proceeds, the embryo will continue to change shape, and cells will become specialized to perform different functions Forming an adult animal, embryos can develop into a: –Juvenile – look like smaller versions of adult animal –Larva – Intermediate stage, w/ no resemblance to adult animal Once the juvenile or larval stages have passed, the animal will continue to grow and develop into an adult.

Symmetry in Animals Asymmetry –Body shape is irregular, no symmetry –Ex: Porifera

Symmetry in Animals Radial Symmetry –Can be divided into equal halves from any point through a central axis point

Symmetry in Animals Bilateral Symmetry: –Can be divided down its length into right and left halves, that are mirror images of one another Anterior (head end), Posterior (tail end) Dorsal (back surface), Ventral (belly surface)

Body Plans in Bilaterally Symmetrical Animals All bilaterally symmetrical animals developed from three embryonic cell layers: ectoderm, endoderm, and mesoderm. Some of these animals also developed fluid- filled body cavities, allowing them to grow larger and develop more complex internal systems. Acoelomates Pseudocoelomates Coelomates

Acoelomates Have all three tissue layers NO body cavity Organs embedded in body tissue Flattened digestive tract that allows for diffusion of nutrients Ex: Flatworms

Pseudocoelomates Pseudocoelom –Body cavity partially lined with mesoderm; develops between the mesoderm and endoderm –Ex: roundworms

Coelomates Coelom –Body cavity completely lined with mesoderm –Most animals are coelomates –Coelom provides space for specialized organs and organ systems –Ex: segmented worms

Body Cavity Comparisons

Protection and Support Invertebrates –NO backbone –Have an exoskeleton Vertebrates –Have a back –Have an endoskeleton Godzilla analogy!