An Introduction to Animal Diversity Chapter 32 An Introduction to Animal Diversity

Kingdom Animalia What are the characteristics of animals?

Reproduction and Development Most animals reproduce sexually, with the diploid stage usually dominating the life cycle

Video: Sea Urchin Embryonic Development 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

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

Many animals have at least one larval stage A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis

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

Paleozoic Era (542–251 Million Years Ago) The Cambrian explosion marks the earliest fossil appearance of many major groups of living animals There are several hypotheses regarding the cause of the Cambrian explosion

Mesozoic Era (251–65.5 Million Years Ago) During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates Coral reefs emerged, becoming important marine ecological niches for other organisms

Cenozoic Era (65.5 Million Years Ago to the Present) The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals Modern mammal orders and insects diversified during the Cenozoic

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

Symmetry Animals can be categorized according to the symmetry of their bodies, or lack of it

Some animals have radial symmetry, the form found in a flower pot LE 32-7a Some animals have radial symmetry, the form found in a flower pot Radial symmetry

LE 32-7b The two-sided symmetry seen in a shovel is an example of bilateral symmetry 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

Tissues Animal body plans also vary according to the organization of the animal’s tissues

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

A pseudocoelom is a body cavity derived from the blastocoel, rather than from mesoderm Body covering (from ectoderm) Digestive tract (from endoderm) Muscle layer (from mesoderm) Pseudocoelom Pseudocoelomate

Acoelomates are organisms without body cavities Body covering (from ectoderm) Wall of digestive cavity (from endoderm) Acoelomate Tissue- filled region (from mesoderm)

Fate of the Blastopore In protostome development, the blastopore becomes the mouth In deuterostome development, the blastopore becomes the anus Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Fate of the blastopore Mouth Anus develops from blastopore Anus Mouth develops Digestive tube

Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree Zoologists recognize about 35 animal phyla Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well

One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

LE 32-10 “Radiata” Deuterostomia Protostomia Bilateria Eumetazoa Porifera Cnidaria Ctenophora Phoronida Ectoprocta Brachiopoda Echinodermata Chordata Platyhelminthes Mollusca Annelida Arthropoda Rotifera Nemertea Nematoda “Radiata” Deuterostomia Protostomia Bilateria Eumetazoa Metazoa Ancestral colonial flagellate

One hypothesis of animal phylogeny is based mainly on molecular data

LE 32-11 “Radiata” “Porifera” Deuterostomia Lophotrochozoa Bilateria 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

Points of Agreement All animals share a common ancestor Sponges are basal animals Eumetazoa is a clade of animals with true tissues Most animal phyla belong to the clade Bilateria Vertebrates and some other phyla belong to the clade Deuterostomia