1Evolution of Animal DiversityBio 103 LectureDr. Largen2What Am I?4 Of some 1.5 million species of organisms known to science– over two-thirds are animals4 Humans have a long history of studying animal diversity– But do we always know what an animal is when we see one?3What is an animal?4 Animals– eukaryotic– multicellular– heterotrophs– lack cell walls– have unique intercellular junctions4What is an animal?4 Animals– Most are diploid• except for haploid eggs and sperm– proceed through a well-defined life cycle5Evolution of animals4 Animal kingdom probably originated from colonial protists– in which cells gradually became more specialized and layered6Evolution of animals4 Ecological, geologic, or genetic factors may have caused the Cambrian explosion in animaldiversity– Cambrian fossils can be classified as ancient representatives of the familiar animal phyla7Characterizing the differences between animal phyla4Animals can be classified according to pattern of development or body structure– Embryologic development• germ layers• blastopore fate– Symmetry– Body plan– Segmentation8Characterizing the differences between animal phyla4Embryologic development– germ layers• what are they?– three cell layers» ectoderm - outer layer» mesoderm - middle layer» endoderm - inner layer– formed at gastrulation» blastula with single layer of cells turns into a 3-layered embryo– foreshadow the future organization of tissues» the three embryonic layers differentiate into the tissues of the adult animal910Characterizing the differences between animal phyla4Embryologic development– germ layers• diploblastic organisms– have two germ layers» ectoderm - outer layer» endoderm - inner layer• triploblastic organisms– have three germ layers» ectoderm - outer layer» mesoderm - middle layer» endoderm - inner layer11Characterizing the differences between animal phyla4Embryologic development– blastopore fate• what is the blastopore?– Early during embryonic development the embryo is a hollow ball of cells– a portion of this hollow ball invaginates inward to form an opening called the blastopore» blastopore can be thought of as the first opening» this opening, the blastopore, becomes either the mouth or the anus of animals with body cavities12Characterizing the differences between animal phyla4Embryologic development– blastopore fate• protostomes– organisms in which the blastopore becomes the mouth» the first (proto) opening becomes mouth• deuterostomes– orgainisms in which the blastopore becomes the anus» the second (deutero) opening becomes the mouth131415Characterizing the differences between animal phyla4Symmetry– refers to the arrangement of body structures in relation to some axis of the body– three types of symmetry• asymmetry• radial symmetry• bilateral symmetry16Characterizing the differences between animal phyla4Symmetry– asymmetry• lack of any defined symmetry• no plane passing through the central axis can divide the organism into halves that are mirror images ofeach other– cutting the organism in half produces dissimilar halves• exhibited by most members of the simplest phylum of animal kingdom– phylum Porifera - the sponges17Characterizing the differences between animal phyla4Symmetry– radial symmetry• can be bisected into roughly equal, mirror-image halves in any two-dimensional plane– multiple plans can be drawn through the central axis, each dividing the organism into two mirror images• exhibited by members of three phyla– phylum Cnidaria - jellyfish, sea anemones, corals– phylum Ctenophora - sea walnuts, comb jellies– phylum Echinodermata - sea stars& urchins, sand dollars» radial symmetry seen in ADULTS in this phylum1819Characterizing the differences between animal phyla4Symmetry– bilateral symmetry• can be bisected into roughly equal, mirror-image halves in only one plane (the sagittal plane)– only one plane can be drawn through the central axis which divides the organism into two mirror images• exhibited in all other animal phyla20Characterizing the differences between animal phyla4Symmetry– bilateral symmetry• a bilaterally symmetrical body plan has a– top - dorsal portion (upper surface)– bottom - ventral portion (lower surface)– front - anterior end (toward head)– back - posterior end (away from head)– side - lateral portion (left or right side)2122Characterizing the differences between animal phyla4Body plan– a widely held system for grouping animal phyla is based on• the presence/absence of a body cavity• type of body cavity23Characterizing the differences between animal phyla4Body plan– what is a body cavity?• a fluid-filled space inside the body– this space may develop between» between the mesoderm and endoderm, in which case its called a psuedocoel» entirely within the mesoderm, in which case its called a coelom24Characterizing the differences between animal phyla4Body plan– four types of body plans• sac-like• acoelomate• pseudocoelomate• coelomate25Characterizing the differences between animal phyla4Body plan– sac-like• simplest of body plans• no formation of three embryonic germ layers• no digestive system• no body cavity• exhibited by phyla that are asymmetrical or radially symmetrical as juveniles262728Characterizing the differences between animal phyla4Body plan– bilaterally symmetrical animals exhibit three basic body plans• acoelomate• pseudocoelomate• coelomate2930Characterizing the differences between animal phyla4Body plan– acoelomate• organisms that lack a body cavity• have a solid body with a single opening to the outside, the mouth• exhibited by– phylum Platyhelminthes - flatworms– a few other minor phyla3132Characterizing the differences between animal phyla4Body plan– pseudocoelomate• organism with a body cavity– called a pseudocoel (pseudo = “false”)– which develops between the mesoderm and endoderm» and therefore it is not completely lined with mesoderm• exhibited by– phylum Nematoda - roundworms– phylum Rotifera - wheel animals3334Characterizing the differences between animal phyla4Body plan– coelomate• organism with a body cavity– called a coelom– which develops entirely within the mesoderm» and therefore it is completely lined with mesoderm• exhibited by many phyla– Mollusca, Annelida, Arthropoda,