The Origin of Animal Diversity Invertebrates

Key features of animals Animals are multicellular, heterotrophic & eukaryotic Most use ingestion as their mode of nutrition The store carbohydrates as glycogen Lack cells walls and have muscle and nervous tissue

Reproduction is usually sexual with flagellated sperm and a larger, non moving egg A developing zygote goes through a series of divisions called cleavage passing through a blastula stage and then a phase called gastrulation

Many have a larval phase as part of their lifecycle METAMORPHOSIS transforms larva into adults

Protostomes & Deuterostomes Shows the origins of phyla & where evolutionary lines diverged TWO main branches of Kingdom Animalia: - Protostomes - Deuterostomes (ex. Chordata- humans) Deutero = second; Stome = mouth

Example: arthropods & molluscs First embryonic cavity: mouth protostomes deuterostomes Example: arthropods & molluscs First embryonic cavity: mouth Type of cleavage: spiral Example: echinoderms & chordates First embryonic cavity: anus (opening for mouth forms later) Type of cleavage: radial

Cleavage Patterns Radial = Deuterostomes Spiral = Protostomes Cleavage: Mitotic divisions without cell growth between divisions (occurs as zygote begins development)

Coelomate Another term for “coelem” is body cavity This cavity if completely lined with a tissue called endoderm/mesoderm This body design allows for more complexity & the formation of internal organs Examples: earthworms (annelids)

Pseudocoelomate The body cavity is partially lined with mesoderm “Pseudo” means false Example. roundworms

Acoelomate Have no body cavity Spaces inside their body are filled by body tissues and fluid Example. flatworms

Specialization of internal organs Complete mesoderm allows for the formation of complex organs (ex. Digestive tract), blood vessels & other complicated organ systems

Gastrulation Follows blastula stage (formation of hollow ball, germ layers begin to form) Layers of embryonic tissue form  will develop into adult body parts The resulting stage is called the gastrula Gastrula: ectoderm, mesoderm & endoderm are formed

Gastrulation During gastrulation, the embryo folds inwards, expands & fills the blastocoel producing embryonic layers of tissue