AN INTRODUCTION TO ANIMAL DIVERSITY CHAPTER 32 AN INTRODUCTION TO ANIMAL DIVERSITY

I. Concept 32.1: What is an Animal? 95% are invertebrates Multicellular Eukaryotic Heterotrophic (ingestive) Lack cell walls Most are mobile Diploid with haploid gametes Sexual reproduction (zygote  blastula  gastrula)

Embryology--Cleavage

9. Carbohydrates stored as glycogen 10. Some produce larva which undergo metamorphosis 11. Specialized systems 12. Two unique types of tissue: nervous tissue and muscle tissue 13. Share the unique homeobox-containing family of regulatory genes know as Hox genes Hox genes play an important role in development of animal embryos

II. Concept 32.2: Animal History A. Common Ancestor 1. May have resembled modern choanoflagellates 2. Choanoflagellates are protists that are the closest living relatives of animals and were probably a colonial, flagellated protist. Such a colony is about 0.02mm high.

III. Concept 32.3: Body Plans A. Phylogeny Define as the evolutionary history of species Based on general features of morphology and development Each major branch represents a grade, (group of animal species that share the same level of organizational complexity) A grade is not necessarily a clade or monophyletic group.

ANIMALS Metazoa Parazoa Eumetazoa Radiata Bilateria Acoelomate Pseudocoelomate Coelomate Deuterostomes Protostomes

B. Major Branches of the Animal Kingdom 1. Subkingdom Parazoa Simple anatomy (lack true tissues) Phylum Porifera 2. Subkingdom Eumetazoa True tissues All other phyla

C. Body Plans A body plan is a set of morphological and developmental traits 1.Symmetry Animals can be categorized by body symmetry or the lack of it a. Radial symmetry (Radiata) -Characterized by a body shaped like a pie or barrel, with many equal parts radiating outward like spokes of a wheel -have oral and aboral sides but no front, back, left, or right surfaces

b. Bilateral symmetry (Bilateria) -Characterized by a body form with a central longitudinal plane dividing the body into two equal but opposite halves -A dorsal (top) and ventral (bottom) sides -Anterior (head) and posterior (tail) ends -Left and right sides -Exhibit cephalization (concentration of nerves and sense organs on anterior end)

SYMMETRY

2. Tissues a. Tissues are collections of specialized cells isolated from other tissues by membranous layers b. During gastrulation (downward and inward movement of cells of blastula), three germ layers form which give rise to the tissues and organs of the animal embryo

Tissues develop from two germ layers (ectoderm or endoderm) c. Diploblastic Tissues develop from two germ layers (ectoderm or endoderm) d. Triploblastic Tissues develop from three germ layers: Ectoderm is the outer most germ layer which develops into outer layer and central nervous system Endoderm is the inner most germ layer and lines the developing digestive tube called the archenteron Mesoderm is the middle layer which is located between ectoderm and endoderm Includes all bilaterians

Germ Layers

3. Body Cavity (Coelom) Defined as a fluid- or air-filled space separating the digestive tract from the outer body wall a. Acoelomate No body cavity between digestive tract and outer body wall Area filled with cells Phylum Platyhelminthes

Acoelomate

Body cavity lined with mesoderm and endoderm Tube within a tube b. Pseudocoelomate Body cavity lined with mesoderm and endoderm Tube within a tube Phyla: Nematoda Rotifera

Pseudocoelomate

c. Coelomate (true body cavity) Body cavity lined with mesoderm Mesenteries connect outer and inner mesoderm and suspend internal organs Phyla: Echinodermata Arthropoda Mollusca Chordata Annelida Functions of the body cavity 1. Fluid cushions the suspended organs, helping to prevent internal injury 2. In soft-bodied coelomates, functions as a hydrostatic skeleton against which muscles can work 3. Enables internal organs to grow and move independently of the other body wall

Coelomate

4. Development--Protostomia vs. Deuterostomia 2 evolutionary lines in coelomates Differ in cleavage, fate of blastopore, and coelom formation Protostomes—mollusks, annelids, arthropods Deuterostomes—echinoderms, chordates

a. Cleavage Protostomes Spiral Cleavage—cleavage diagonal to the embryo’s vertical axis Deuterostomes Radial Cleavage—cleavage either parallel or perpendicular to embryo’s vertical axis

b. Determination  Protostomes Determinate Cleavage—developmental fate of each cell determined very early -A cell from 4-cell stage will not develop fully  Deuterostomes Indeterminate Cleavage—early cells retain ability to develop into complete embryo if isolated from other cells -Makes possible identical twins and embryonic stem cells

Cleavage

c. Coelom Formation Protostomes Schizocoelous—the splitting of solid masses of mesoderm forms the coelom Deuterostomes Enterocoelous—the mesoderm buds from the wall of the archenteron to form the coelom

Coelom Formation

d. Fate of Blastopore Blastopore—first opening of archenteron (gut) which forms from blastula during gastrulation Protostomes --Blastopore becomes the mouth Deuterostomes --Blastopore becomes the anus

Fate of the Blastopore

IV. Concept 32.4: New Views of Animal Phylogeny One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons

Morphological Characteristics

One hypothesis of animal phylogeny is based mainly on molecular data

Molecular Studies

A. Points of Agreement All animals share a common ancestor Sponges are basal animals Eumetazoa is a clade of animals (eumetazoans) with true tissues Most animals phyla belong to the clade Bilateria and are called bilaterians Chordates and some other phyla belong to the clade Deuterostomia

B. Progress in resolving Bilaterian Relationships 1. The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes 2. In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa a. Ecdysozoans shed their exoskeletons through a process called ecdysis (Arthropoda and Nematoda) b. Some lophotrochozoans have a feeding structure called a lophophore ( Mollusca, Annelida, Rotifera, Platyhelminthes) c. Other phyla go through a distinct developmental stage called the trochophore larva(Mollusca and Annelida)

TERMS: Zygote Cleavages Blastula Gastrula Ectoderm Endoderm Mesoderm Blastopore Archenteron Metamorphosis Radial symmetry Bilateral symmetry Cephalization Acoelomate Pseudocoelomate Coelomate Anterior Posterior Dorsal Ventral

Ecdysis

Trochophore Larva

You should now be able to: List the characteristics that combine to define animals Distinguish between the following pairs or sets of terms: radial and bilateral symmetry; grade and clade of animal taxa; diploblastic and triploblastic; spiral and radial cleavage; determinate and indeterminate cleavage; acoelomate, pseudocoelomate, and coelomate grades Compare the developmental differences between protostomes and deuterostomes Compare the alternate relationships of annelids and arthropods presented by two different proposed phylogenetic trees Distinguish between ecdysozoans and lophotrochozoans