Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 32 An Introduction to Animal Diversity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers There are exceptions to nearly every criterion for distinguishing animals from other life forms Several characteristics, taken together, sufficiently define the group

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutritional Mode Animals are heterotrophs that ingest their food Animals are multicellular eukaryotes Their cells lack cell walls Their bodies are held together by structural proteins such as collagen Nervous tissue and muscle tissue are unique to animals

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproduction and Development Most animals reproduce sexually, with the diploid stage usually dominating the life cycle After a sperm fertilizes an egg, the zygote undergoes cleavage, leading to formation of a blastula The blastula undergoes gastrulation, forming embryonic tissue layers and a gastrula

LE 32-2_3 Zygote Eight-cell stage Cleavage Blastula Cross section of blastula Cleavage Blastocoel Endoderm Ectoderm Gastrula Blastopore Gastrulation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings All animals, and only animals, have Hox genes that regulate the development of body form Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 32.2: The history of animals may span more than a billion years The animal kingdom includes not only great diversity of living species but also the even greater diversity of extinct ones The common ancestor of living animals may have lived 1.2 billion–800 million years ago This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals

LE 32-3 Stalk Single cell

LE 32-4 Hollow sphere of unspecialized cells (shown in cross section) Somatic cells Colonial protist, and aggregate of identical cells Gastrula-like “protoanimal” Beginning of cell specialization Reproductive cells Infolding Digestive cavity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Symmetry Animals can be categorized according to the symmetry of their bodies, or lack of it

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some animals have radial symmetry, the form found in a flower pot

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The two-sided symmetry seen in a shovel is an example of bilateral symmetry

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bilaterally symmetrical animals have: – A dorsal (top) side and a ventral (bottom) side – A right and left side – Anterior (head) and posterior (tail) ends – Cephalization, the development of a head

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tissues Animal body plans also vary according to the organization of the animal’s tissues Tissues are collections of specialized cells isolated from other tissues by membranous layers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animal embryos have concentric layers called germ layers that form tissues and organs Ectoderm is the germ layer covering the embryo’s surface Endoderm is the innermost germ layer Diploblastic animals have ectoderm and endoderm Triploblastic animals also have an intervening mesoderm layer

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body Cavities In triploblastic animals, a body cavity may be present or absent A true body cavity is called a coelom and is derived from mesoderm

LE 32-8a Coelom Coelomate Body covering (from ectoderm) Digestive tract (from endoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A pseudocoelom is a body cavity derived from the blastocoel, rather than from mesoderm

LE 32-8b Body covering (from ectoderm) Digestive tract (from endoderm) Muscle layer (from mesoderm) Pseudocoelom Pseudocoelomate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acoelomates are organisms without body cavities

LE 32-8c Body covering (from ectoderm) Wall of digestive cavity (from endoderm) Acoelomate Tissue- filled region (from mesoderm)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protostome and Deuterostome Development Based on early development, many animals can be categorized as having protostome or deuterostome development

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cleavage In protostome development, cleavage is spiral and determinate In deuterostome development, cleavage is radial and indeterminate

LE 32-9a Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Eight-cell stage Radial and indeterminate Cleavage Eight-cell stage Spiral and determinate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Coelom Formation In protostome development, the splitting of solid masses of mesoderm to form the coelomic cavity is called schizocoelous development In deuterostome development, formation of the body cavity is described as enterocoelous development

LE 32-9b Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Coelom formation Coelom Archenteron Blastopore Mesoderm Enterocoelous: folds of archenteron form coelom Coelom BlastoporeMesoderm Schizocoelous: solid masses of mesoderm split and form coelom

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fate of the Blastopore In protostome development, the blastopore becomes the mouth In deuterostome development, the blastopore becomes the anus

LE 32-9c Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Fate of the blastopore Mouth Anus develops from blastopore Anus Mouth Mouth develops from blastopore Anus Digestive tube