Animal Diversity

Extends far beyond humans and other animals we may encounter

The Animal Kingdom

Figure 32.1

Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers

Several characteristics of animals◦ Sufficiently define the group

• Animals are heterotrophs

– That ingest their food

Nutritional Mode

• Animals are multicellular eukaryotes

• Their cells lack cell walls

Cell Structure and Specialization

• Most animals reproduce sexually

– With the diploid stage usually dominating the life cycle

• 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

Reproduction and Development

Early embryonic development in animals

Zygote

Cleavage

Eight-cell stage

Cleavage

Blastula Cross section of blastula

Blastocoel

Blastocoel

Gastrula Gastrulation

Endoderm

Ectoderm

Blastopore

• Early members of the animal fossil record

– Include the Ediacaran fauna

Neoproterozoic Era (1 Billion–524 Million Years Ago)

• The Cambrian explosion

– Marks the earliest fossil appearance of many major groups of living animals

– Is described by several current hypotheses

Paleozoic Era (542–251 Million Years Ago)

• During the Mesozoic era

– Dinosaurs were the dominant terrestrial vertebrates

– Coral reefs emerged, becoming important marine ecological niches for other organisms

Mesozoic Era (251–65.5 Million Years Ago)

• The beginning of this era

– Followed mass extinctions of both terrestrial and marine animals

• Modern mammal orders and insects

– Diversified during the Cenozoic

Cenozoic Era (65.5 Million Years Ago to the Present)

• Animals can be categorized

– According to the symmetry of their bodies, or lack of it

• Some animals have radial symmetry

– Like in a flower potRadial 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.

Symmetry

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.

Some animals exhibit bilateral symmetryOr two-sided symmetry

• 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

Protostome and Deuterostome Development

In protostome development◦ Cleavage is spiral and determinate

In deuterostome development◦ Cleavage is radial and indeterminate

Cleavage

Protostome development(examples: molluscs, annelids,

arthropods)

Deuterostome development(examples: echinoderms,

chordates)

Eight-cell stage Eight-cell stage

Spiral and determinate Radial and indeterminate

(a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage.

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

Coelom Formation

Figure 32.9b

Archenteron

Blastopore MesodermCoelom

BlastoporeMesoderm

Schizocoelous: solidmasses of mesodermsplit and form coelom

Enterocoelous:folds of archenteronform 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).

In protostome development◦ The blastopore becomes the mouth

In deuterostome development◦ The blastopore becomes the anus

Fate of the Blastopore

Figure 32.9c

Anus

Anus

Mouth

Mouth

Mouth developsfrom blastopore

Anus developsfrom blastopore

Digestive tube