Chapter 32

Introduction to Animal Diversity

The animal kingdom extends far beyond humans and other animals we may encounter

1.3 million living species of animals have been identified

Animals utilize a heterotrophic nutritional model – having to ingest their food.

Animals are multicellular eukaryotes that primarily reproduce sexually.

After fertilization the zygote undergoes cleavage - rapid cell division

Animals are multicellular eukaryotes that primarily reproduce sexually.

Leading to the formation of a blastula

Animals are multicellular eukaryotes that primarily reproduce sexually.

Forming the different layers of embryonic tissues through gastrulation.

All animals, and only animals, have Hox genes that regulate development.

Highly conserved, but produce a wide diversity of animal morphology.

Cambrian explosion (535 to 525 MYA) earliest fossil appearance of many major groups of living animals.

Cambrian explosion (535 to 525 MYA) earliest fossil appearance of many major groups of living animals.

Diversity increases through Paleozoic but punctuated by mass extinctions

Cambrian explosion (535 to 525 MYA) earliest fossil appearance of many major groups of living animals.

Animals begin to make impact on land – 460 MYAVertebrates transition to land – 360 MYA

During Mesozoic (251-65.5 MYA) coral reefs emerge and dinosaurs dominant.

65.5 MYA the start of the Cenozoic era followed mass extinction and modern mammal orders diversify.

Animals characterized by morphological and developmental traits – body plans

Bilaterally symmetrical animals have dorsal, ventral, anterior, posterior, right and left sides. Also, cephalization.

Three germ layers give rise to the tissues and organs of the animal embryo:• Endoderm• Mesoderm• Ectoderm

Diploblastic animals have ectoderm and endoderm.

Triploblastic have all three germ layers.

Coelomates are triploblastic animals that possess a true body cavity called a coelom.

Pseudocoelomates have a cavity supported by hydrostatic pressure.

Acoelomates lack a coelom.

Many animals can be categorized as have protostome or deuterostome development.

Based on morphology data. Based on molecular data.

About three dozen animal phyla recognized, two phylogenetic hypotheses developed.