Biology 1202: Animal Diversity (Chapter 32)

Animals

Multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers. Their cells are supported by structural proteins such as collagen and their nervous tissues and muscle tissue are unique characteristics.

Animal reproduction

Most reproduce sexually, with the diploid stage typically dominating the life cycle.

Cleavage

Rapid cell division after the sperm fertilizes the egg that leads to the formation of a multicellular, hollow blastula. The blastula then undergoes gastrulation, forming a gastrula with different layers of embryonic tissues.

Larva

A sexually immature and morphologically distinct juvenile from the adult.

Hox genes

A subset of homeobox genes, the Hox genes are a family of developmental genes that regulate the expression of other genes, body formation, and produces a wide range of animal morphology.

Neoproterozoic Era

1 BYA to 541 MYA, microscopic fossils of animal embryos have been found in the rocks, in addition to evidence of predation.

Paleozoic Era

541 MYA to 252 MYA, Cambrian Explosions marks the earliest fossil appearance of many major groups of living animals. Most of the organisms had the following traits:

1. Bilaterally symmetric

2. Complete digestive tract

3. One-way digestive tract

Causes of the Cambrian Explosion?

1. New predator-prey relationships

2. A rise in atmospheric oxygen

3. The evolution of the Hox genes and the addition of new microRNAs.

Transition to land

Vertebrates began to move onto land around 365 MYA, but made an impact around 450 MYA.

Mesozoic Era

252 to 66 MYA, the emergence or the first mammals, coral reefs, the diversification of flowering plants and insects, and the era of dinosaurs.

Cenozoic Era

66 MYA to present, followed mass extinctions of both terrestrial and marine animals. The global climate cooled and mammals increased in size and began to fill the now empty ecological niches.

Radial symmetry

Animals have a top and a bottom, but no front, back, left, or right. Typically sessile or planktonic, meaning they drift or weakly swim.

Bilateral symmetry

Animals have a right and a left side, a top (dorsal) and bottom (ventral) side, and a front and back end. Typically very active and have a central nervous system.

Tissues

Collections of specialized cells isolated from other tissues by membranous layers.

Ectoderm

The germ layer covering the embryo’s surface.

Archenteron

The developing digestive tube.

Endoderm

The innermost germ layer that lines the archenteron.

Mesoderm

An intermediate tissue layer between the ectoderm and endoderm.

Diploblastic animals

Animals that only have an ectoderm and endoderm. Includes cnidarians (jellyfish) and a few other groups.

Triploblastic animals

Have all three derm layers. All bilaterally symmetrical animals are triploblastic. Most possess a body cavity.

Coelom

A true body cavity, it is derived from mesoderm. It’s functions are:

1. Fluid cushions the suspended organs

2. Fluid acts like a skeleton against which muscles can work

3. The cavity enables internal organs to grow and move independently of the outer body wall.

Coelomates

Coelomates are triploblastic animals that possess a true coelom. A tissue layer lines the coelom and suspends the internal organs.

Pseudocoelom

A body cavity derived from the mesoderm and the endoderm. The internal organs are free floating.

Acoelamates

Triploblastic animals that lack a body cavity.

Grade

A group of whose members share key biological features. Not necessarily a clade, which is an ancestor and all of its descendants.

Protostome development

The cleavage is spiral and determinate. The fate of each embryonic cell is determined early in development. The splitting of the mesoderm forms the coelom. The blastopore develops into the mouth.

Deuterostome development

The cleavage is radial and indeterminate. Every cell in the early stages can develop into a complete embryo. The mesoderm buds from the wall of the archenteron to form the coelom. The anus develops from the blastopore.

Animal phylogenies

Based on things such as…

1. whole genome analysis

2. morphological traits

3. ribosomal RNA (rRNA) genes

4. Hox genes

5. protein-coding nuclear genes and mitochondrial genes

Living animal relationships

1. All animals share a common ancestor

2. Sponges are the sister group to all other animals

3. Eumetazoa (“true animals”) is a clade of animals with tissues.

4. Most animal phyla belong to the clade Bilateria

5. There are three major clades of bilaterian animals, all of which are invertebrates except Chordata.

Bilaterian clades

1. Deuterostomia

2. Ecdysozoa

3. Lophotrochozoa

Deuterostomia

This clade includes both vertebrates and invertebrates, like hemichordates,. echinoderms, and chordates.

Ecdysozoa

Composed entirely of invertebrates, they secrete external skeletons and shed them through ecdysis.

Lophotrochozoa

Some have a feeding structure called a lophophore, others have a distinct trochophore larva developmental stage.