Lec 32: Animal Diversity

Reproduction and Development

• reproduce sexually, with the diploid stage dominating the life cycle

• sperm and egg cells by meiotic division

• Cleavage lead to formation of blastula

• blastula undergoes gratulation, forming gastrula with diff. layers of embryonic tissues

Choanoflagellates

• are the closest living relatives to animals

• common ancestor to modern choanoflagellates

Multicellularity

• new ways for cells to adhere (attach) and signal (communicate) to each other

Neoproterozic Era

• form the Ediacaran biota, for the Ediacara Hilla of Australia

• Ediacaran fossils are closely related to molluscs, sponges, or cnidarians

Paleozoic Era

• Cambrian explosion: period of rapid animal diversification

• first large animal fossil

• bilaterians fossils that are: bilaterally symmetric form, complete digestive tract, mouth and anus at opposite ends

• arthropods first to adapt to land and influenced plants

Symmetry

• animals compared based om body symmetry or lack of

• radially symmetrical

• bilateral

radially symmetrical

• body parts arranged around a singel central axis

• central axis divides the animal into 4 parts

bilateral

• arranged around two axes, the head-tail axis and the dorsal- ventral axis

• one slice divides into halves, left and right side

• have a dorsal and ventral side

• head end and tail end

Ectoderm

• covers the embryo surface

• gives rise to the outer covering

• central nervous system

• outside skin

Endoderm

• innermost layer

• forms the gut

• gives rise to the lining of the digestive tract and organs

• stomach, brain, spine

Diploblastic

• animals- cnidarians

• only have ectoderm and endoderm

Triploblastic

• bilaterally symmetrical animals

• have third germ layer

Mesoderm

• fills the space between ectoderm and endoderm

• muscle and most organs

Body cavities

• triploblastic animlas

• fluid or air-filled space between the digestive tract

• outer body wall

• protect organs

• enables internal organs to grow and move independently of th eouter body wall

Coelom

• a body cavity surrounded by tissues derived from mesoderm

• coelom = mesoderm

Hemocoel

• body cavity formed between the mesoderm and endoderm

• filled with hemolymph, fluid that transport nutrients and waste

• molluscs, use as primary body cavity

Protostome development

mouth development

Deuterostome development

anus development

Spiral Cleavage

• the planes of cell division are diagonal to the vertical axis of the embryo

Determinate cleavage

• determines the developmental fate of each embryonic cell very ealry

Radial cleavage

the planes of division are either parallel or perpendicular to the embryo’s vertical axis

indeterminate cleavage

each cell produced by early cleavage is able to form a complete embryo

Blastopore

• an indentation in the gastrula that leads to the formation of the archenteron

• in protostome development, becomes the mouth

• in deuterostome development, becomes the anus

relationship among living animals and their phylogeny

• all animals share a common ancestor

• sponges are the sister group to all other animals

• Eumetazoa is a clade of animals with tissues

• most animals phyla belong to the clade bilateria

• there are three major clades of bilaterian animals

Deuterostomia

• may be invertebrates or vertebrates

• include echinoderms and chordates