Chapter 32

Characteristics that Define Animals Nutritional modes Ingest organic molecules and digest them via enzymes Cell structure and specialization Multicellular with structural proteins (collagen) for support Muscle and nervous tissue to send signals and allow mobility Reproduction and development Reproduce sexually with diploid (2n) stage as dominating Born to resemble adult or as larva that undergoes metamophosis Genes regulate expression of other genes Homeoboxes, common DNA sequences, known as Hox genes

Embryonic Development Cleavage, rapid cell divisions without significant growth Creates a similar sized blastula, or hollow ball of cells Gastrulation results from inward folding of the embryo Produces layers of embryonic tissue, endo- and ectoderm Layers develop into adult structures

Symmetry Asymmetry Most sponges Radial symmetry Top and bottom, but no front, back, or sides sessile Bilateral symmetry Anterior (front) and posterior (back), dorsal (top) and ventral (bottom) Most demonstrate cephalization Sensory structures anteriorly Motile with complex movements

Tissues True tissues are collections of specialized cells isolated from others by membranous layers Sponges lack true tissues Gastrulation forms embryonic layers of tissue, called germ layers Ectoderm covers outer part of embryo Outer layer or animal and some nervous systems Endoderm forms innermost layer Lines developing digestive tube or archenteron, becomes digestive tract lining, liver, and lungs Diploblastic animals, i.e. cnidarians and comb jellies Mesoderm in all animals with bilateral symmetry Muscles and most other organs Triploblastic animals, i.e. flatworms to arthropods to vertebrates

Body Cavities Presence of absence classifies bilateral (triploblastic) animals Space separating digestive tract from outer body wall, called a coelom Coelomates All mesoderm, joined dorsally and ventrally Pseudocoelomates Formed from endo- and mesoderm Acoelomates Lack a body cavity Allows independent organ movement, protects, and forms a fluid skeleton

Protostomes and Deuterostomes Cleavage P: spiral cleavage, planes of division are diagonal; determinate cleavage, fate of each cell determined early D: radial cleavage, planes parallel or perpendicular; indeterminate cleavage, each cell retains capacity to develop Coelom formation P: solid masses of mesoderm split to form D: mesoderm buds from archenteron Blastopore fate P: mouth before anus D: anus before mouth

Kingdom Animalia Hypotheses 35 phyla currently recognized Grouped through shared-derived characteristics into clades What does this mean? ‘Traditional’ morphological character Molecular data based on DNA has provided new hypotheses ‘New’ molecular sequences data Two hypothesis have several points of agreement

Major Defining Features All animals share a common ancestor Kingdom animalia is monophyletic Sponges are basal animals Branch from base of both trees Eumetazoa is a clade of animals with true tissues Basal members are diploblastic with radial symmetry Most animals form a bilateria clade Bilateral symmetry and 3 germ layers Chordates form a deuterostomia clade

Disagreements Morphological has bilaterians as 2 clades Protostomes and deuterostomes Arthropods and annelids are protostomes with segmented bodies Molecular has bilaterians as 3 clades Deuterostomia Arthropods and annelids not related Group of acoelomate flatworms not represented in morphological hypothesis Basal bilaterians, not phylum platyhelminthes Lophotrochozoa Lophophore develops, crown of ciliated tentacles for feeding Distinctive trochophore larva stage Ecdysozoa are animals that secrete exoskeletons Ecdysis, molting old exoskeleton

Morphological vs Molecular Trees