Overview Welcome to Your Kingdom The animal kingdom

Overview: Welcome to Your Kingdom • The animal kingdom extends far beyond humans and other animals we may encounter Video: Coral Reef Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 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 formation of a blastula • The blastula undergoes gastrulation, forming embryonic tissue layers and a gastrula Video: Sea Urchin Embryonic Development Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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

• Many animals have at least one larval stage • A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Concept 32. 3: Animals can be characterized by “body plans” • Zoologists sometimes categorize animals according to morphology and development • A grade is a group of animal species with the same level of organizational complexity • A body plan is the set of traits defining a grade 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

LE 32 -7 a Radial symmetry

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

LE 32 -7 b Bilateral symmetry

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

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

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

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

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

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

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

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

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

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

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

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