Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 32 An Introduction to Animal Diversity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 32.1: Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutritional Mode Animals are heterotrophs – That ingest their food

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell Structure and Specialization Animals are multicellular eukaryotes Their cells lack cell walls

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings After a sperm fertilizes an egg – The zygote undergoes cleavage, leading to the formation of a blastula The blastula undergoes gastrulation – Resulting in the formation of embryonic tissue layers and a gastrula

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zygote Cleavage Eight-cell stage Cleavage Blastula Cross section of blastula Blastocoel Gastrula Gastrulation Endoderm Ectoderm Blastopore Figure 32.2 In most animals, cleavage results in the formation of a multicellular stage called a blastula. The blastula of many animals is a hollow ball of cells. 3 The endoderm of the archenteron de- velops into the tissue lining the animal’s digestive tract. 6 The blind pouch formed by gastru- lation, called the archenteron, opens to the outside via the blastopore. 5 Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer). 4 Only one cleavage stage–the eight-cell embryo–is shown here. 2 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 1 Early embryonic development in animals

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 common ancestor of living animals – May have lived 1.2 billion–800 million years ago – May have resembled modern choanoflagellates, protists that are the closest living relatives of animalschoanoflagellates Figure 32.3 Single cell Stalk

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Was probably itself a colonial, flagellated protist Figure 32.4 Colonial protist, an aggregate of identical cells Hollow sphere of unspecialized cells (shown in cross section) Beginning of cell specialization Infolding Gastrula-like “protoanimal” Somatic cells Digestive cavity Reproductive cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) (b) Neoproterozoic Era (1 Billion–524 Million Years Ago) Early members of the animal fossil record – Include the Ediacaran faunaEdiacaran Figure 32.5a, b

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Paleozoic Era (542–251 Million Years Ago) The Cambrian explosion – Marks the earliest fossil appearance of many major groups of living animals – Is described by several current hypotheses Figure 32.6 predator/prey rising O 2 levels Hox genes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mesozoic Era (251–65.5 Million Years Ago) During the Mesozoic eraMesozoic era – Dinosaurs were the dominant terrestrial vertebrates – Coral reefs emerged, becoming important marine ecological niches for other organisms – Gymnosperms, and later angiosperms, emerged

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cenozoic Era Cenozoic Era (65.5 Million Years Ago to the Present) The beginning of this era – Followed mass extinctions of both terrestrial and marine animals Modern mammals, insects, and angiosperms – Diversified during the Cenozoic

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 32.3: Animals can be characterized by “body plans” One way in which zoologists categorize the diversity of animals – Is according to general features of morphology and development

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A group of animal species that share the same level of organizational complexity is known as a grade A body plan is the set of morphological and developmental traits integrated into a functional whole

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 – Like in a flower pot Figure 32.7a Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images. (a)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some animals exhibit bilateral symmetry – Or two-sided symmetry Figure 32.7b Bilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves. (b)

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 separated from other tissues by membranous layers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animal embryos form germ layers, including ectoderm, endoderm, and mesoderm Diploblastic animals have two germ layers Triploblastic animals have three germ layers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body Cavities In triploblastic animals – A body cavity may be present or absent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A true body cavity – Is called a coelom and is derived from mesoderm Figure 32.8a Coelom Body covering (from ectoderm) Digestive tract (from endoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm. (a)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A pseudocoelom – Is a body cavity derived from the blastocoel, rather than from mesoderm Figure 32.8b Pseudocoelom Muscle layer (from mesoderm) Body covering (from ectoderm) Digestive tract (from endoderm) Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm. (b)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Organisms without body cavities – Are considered acoelomates Figure 32.8c Body covering (from ectoderm) Tissue- filled region (from mesoderm) Digestive tract (from endoderm) Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall. (c)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protostome and Deuterostome Development Based on certain features seen in early development – Many animals can be categorized as having one of two developmental modes: protostome development 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 Figure 32.9a Protostome development (examples: molluscs, annelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Eight-cell stage Spiral and determinate Radial and indeterminate (a) Cleavage. In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Coelom Formation In protostome development – The splitting of the initially 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 Figure 32.9b Archenteron Blastopore Mesoderm Coelom Blastopore Mesoderm Schizocoelous: solid masses of mesoderm split and form coelom Enterocoelous: folds of archenteron form coelom Coelom (b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development).

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 Figure 32.9c Anus Mouth Mouth develops from blastopore Anus develops from blastopore Digestive tube

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree The current debate in animal systematics has led to the development of two main phylogenetic hypotheses

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings morphological and developmental Figure PoriferaCnidaria Ctenophora Phoronida Ectoprocta Brachiopoda Echinodermata Chordata Platyhelminthes Mollusca Annelida Arthropoda Rotifera Nemertea Nematoda “ Radiata ” Deuterostomia Protostomia Bilateria Eumetazoa Metazoa Ancestral colonial flagellate Calcarea Silicarea Ctenophora Cnidaria Echinodermata Chordata Brachiopoda Phoronida Ectoprocta Platyhelminthes Nemertea Mollusca Annelida Rotifera Nematoda Arthropoda “Radiata” “Porifera” Deuterostomia Lophotrochozoa Ecdysozoa Bilateria Eumetazoa Metazoa Ancestral colonial flagellate Figure molecular