Animal Evolution and Characteristics

Choanoflagellates

Unicellular or colonial protists with one flagellum surrounded by microvilli

Diplontic life cycles

Life cycles where animals have only a haploid phase

Suspension feeders

Organisms that trap particles by beating flagella and phagocytosing

Cadherins

Cell adhesion proteins involved in sticking cells together

Synapomorphies of animals

multicellularity; unique junctions between cells; extracellular matrix; How genes

Indeterminate cleavage

Embryonic development where cells retain capacity to form complete organisms

Determinate cleavage

Embryonic development where cells are already determined to form specific parts

Blastula

Hollow ball of cells with a central fluid-filled space

Gastrulation

Process where some cells move from the outside to the inside of the blastula

Diploblast

Embryo with two tissue layers: ectoderm and endoderm

Triploblast

Embryo with three tissue layers: ectoderm, endoderm, and mesoderm

Protostomes

mouth first

Deuterostomes

mouth second

Acoelomate

Animals lacking a fluid-filled cavity between gut and ectoderm

Pseudocoelomate

Animals with a fluid-filled cavity not completely lined by mesoderm

Coelomate

Animals with a fluid-filled cavity completely lined by mesoderm

Direct development

Zygote to adult without a larval stage

Indirect development

Zygote to adult with a distinct larval stage

Planktonic larvae

Larval stage for dispersal away from place of birth

Chordates

Animals with a backbone

What is the sister taxon to the animals? What links animals to them?

Choanoflagellates; presence of choanoflagellate-like cells in sponges and some other animals

How did metazoans evolve from a choanocyte-like ancestor?

- evolution of proteins
- genes for many of these proteins were present in the common ancestor were present in animals and choanocytes

Describe the types of symmetry and various characters of development to categorize animal body plans.

Radial and bilateral; Cleavage patterns, number of embryonic tissue layers, fate of the blastopore, presence of body cavities

Describe the main features of animal phylogeny, and who belongs in each group

1. All animals (metazoa) are monophyletic
2. Most animal phyla belong to clade Bilateria
3. The Bilateria is broken up into three major clades: Deuterostomes, Lophotrochozoans, and Ecdysozoans

When did animals evolve? When did eumetazoans evolve? When did fossils of animals start to appear in the fossil record?

770 mya; 680 mya; 560 mya

What caused the Cambrian explosion?

Increases in predation, increases in atmospheric oxygen allowed animals to become larger

Describe the characters and basic biology of sponges, placozoans, cnidarians, and ctenophores

- sponges: Often asymmetric (neither radial nor bilateral), No true tissue layers (so neither diplo nor triploblastic), No mouth or stomach, or any kind of digestive system, No nerves, No muscles
- Cnidaria and Ctenophora: radial symmetry, diploblastic. Have a digestive system, nerves, muscles