CH 24 WHAT IS AN ANIMAL?

CHARACTERISTICS OF ALL ANIMALS

Eukaryotic

Multicellular

Specialized cells (tissues & organs)

Ingestive heterotrophs

1.5 million species

STRUCTURES FOR SUPPORT AND DEVELOPMENT

Exoskeletons – - hard or tough outer coverings - provide a framework for support- protect soft body tissues- prevent water loss- protection against predators

Found on many invertebrates

Invertebrates – animals without backbones

- 95-99% of animal species

- most have an exoskeleton

- exoskeletons are shed to make a new one as the animal grows

- Some invertebrates, sea urchins and sea stars; have internal skeletons (endoskeletons)

Invertebrates Examples – animals without backbones

- Sponges, Cnidarians – first animals to evolve from a multicellular ancestor

- Worms: flatworms, roundworms, segmented worms

- Mollusks: octopus, snails, squids, clams

- Arthropods: crustaceans, spiders, insects- Echinoderms: sea stars, sea urchins,

sand dollars

- Invertebrate Chordates: lancelet, tunicates

Vertebrates – animals with a backbone Endoskeleton – internal

skeletons grow with the animal

- calcium carbonate -sea urchins/sea stars (invertebrates)

- cartilage – sharks

- bone – fishes, amphibians, reptiles, birds, mammals

SEXUAL REPRODUCTION (MOST)

Sperm + Egg = Zygote

Cleavage - - > zygote divides

Embryo -> an organism in the early stages of development

CELL LAYERS(Most have three layers)

Ectoderm - outer layer (skin & nervous tissue)

Endoderm - inner layer (digestive organs)

Mesoderm – middle layer (muscles, circulatory, excretory and respiratory systems)

SYMMETRYRadial - round, or sphere shaped

Bilateral – right and left halves form a mirror image

Asymmetrical – no definite shape

BODY PLANESDorsal - back surfaceVentral - belly surfaceAnterior - top (head)Posterior - tail end

BODY CAVITIES

Coelum - fluid-filled cavity - mesoderm (earthworms)

Acoelomate - no body cavity (flatworms)