Chapter 18: Evolution of invertebrate diversity Brief tour animal kingdom diversity - 9 of 35 animal phyla Evolving for perhaps one billion years

What is an animal? Multicellular Heterotrophic Eukaryotes Obtain nutrients by ingestion

Other distinctive features: No cell wall Extracellular structural proteins Unique intercellular junctions Muscle cells for movement Nerve cells for conducting impulses Life cycles

Fig. 18-1b-1 Egg Meiosis 1 Sperm Adult Haploid (n) Diploid (2n) Key

Fig. 18-1b-2 Egg Meiosis 1 2 Sperm Zygote (fertilized egg) Haploid (n) Diploid (2n) Key Adult

Fig. 18-1b-3 Egg Meiosis Sperm Zygote (fertilized egg) Eight-cell stage Adult Haploid (n) Diploid (2n) Key

Fig. 18-1b-4 Egg Meiosis Sperm Zygote (fertilized egg) Eight-cell stage Adult Blastula (cross section) Haploid (n) Diploid (2n) Key

Fig. 18-1b-5 Egg Meiosis Sperm Zygote (fertilized egg) Eight-cell stage Adult Blastula (cross section) Early gastrula (cross section) Haploid (n) Diploid (2n) Key

Fig. 18-1b-6 Egg Meiosis Sperm Zygote (fertilized egg) Eight-cell stage Adult Blastula (cross section) Ectoderm Endoderm Internal sac Later gastrula (cross section) Future mesoderm Early gastrula (cross section) Haploid (n) Diploid (2n) Key

Fig. 18-1b-7 Egg Meiosis Sperm Zygote (fertilized egg) Eight-cell stage Adult Blastula (cross section) Digestive tract Larva Ectoderm Endoderm Internal sac Later gastrula (cross section) Future mesoderm Early gastrula (cross section) Haploid (n) Diploid (2n) Key

Fig. 18-1b-8 Egg Meiosis Sperm Zygote (fertilized egg) Eight-cell stage Adult Metamorphosis Blastula (cross section) Digestive tract Larva Ectoderm Endoderm Internal sac Later gastrula (cross section) Future mesoderm Early gastrula (cross section) Haploid (n) Diploid (2n) Key

Hox genes Control development Used to investigate phylogenies Provided insights for mechanisms of evolution

Origins? Common ancestor 1 billion years ago choanoflagellates

Fig. 18-2a Colonial protist, an aggregate of identical cells Hollow sphere of unspecial- ized cells Reproductive cells Beginning of cell specialization Infolding Gastrula-like “proto-animal” Somatic cells Digestive cavity Hypothesis for evolution of the first animal… No fossils of this. :(

Cambrian Explosion 542 million years ago Dramatic increase in diversity of animal fossils over short period (15 my) Why the sudden increase? Hox genes’ role

Most animals are invertebrates 35 or so animal phyla, All but one are invertebrates!

Body plans Symmetry Tissue organization Body cavity?

Fig. 18-3a Top Bottom Anterior end Dorsal surface Ventral surface Posterior end Symmetry defines ones lifestyle

Organization of tissues True tissues = collections of specialized cells that perform specific functions Endoderm Ectoderm Mesoderm

Body cavity A fluid filled space between the digestive tract and the outer body wall Cushions internal organs Hydrostatic skeleton

Fig. 18-3d Digestive sac (from endoderm) Body covering (from ectoderm) Tissue-filled region (from mesoderm) Flatworm No body cavity

Fig. 18-3c Body covering (from ectoderm) Muscle layer (from mesoderm) Digestive tract (from endoderm) Pseudocoelom Round worm Pseudocoelom

Fig. 18-3b Coelom Digestive tract (from endoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Segmented worm True Coelom

Protostomes opening becomes the mouth Deuterostomes opening becomes the anus

Fig Ancestral colonial protist No true tissues Radial symmetry True tissues Bilateral symmetry Eumetazoans Bilaterians Protostomes Deuterostomes Sponges Cnidarians Echinoderms Chordates Flatworms Molluscs Annelids Arthropods Nematodes

Sponges

Fig. 18-5d Pores Amoebocyte Skeletal fiber Central cavity Choanocyte in contact with an amoebocyte Flagella Water flow Choanocyte

Sponges… Suspension feeders Sessile Simplest of all animals Arose early in animal lineage

Fig Ancestral colonial protist No true tissues Radial symmetry True tissues Bilateral symmetry Eumetazoans Bilaterians Protostomes Deuterostomes Sponges Cnidarians Echinoderms Chordates Flatworms Molluscs Annelids Arthropods Nematodes

Cnidarians

Fig. 18-6d Tentacle Prey “Trigger” Discharge of thread Cnidocyte Coiled thread Capsule (nematocyst)

Flatworms Simplest bi-lateral animal 1 mm to 20 m in length! Free-living and parasitic

Fig. 18-7a Gastrovascular cavity Mouth Nerve cords Eyespots Nervous tissue clusters Bilateral symmetry

Flukes Many have complex life cycles

Fig. 18-7b Units with reproductive structures Scolex (anterior end) Hooks Sucker mmmm…. Tape worms!

Nematodes Pseudocoelem Three tissue layers Complete diestive tract Cuticle Mouth

Free living Live virtually everywhere there is rotting organic matter Live in large numbers Important decomposers Some are predators

Caenorhabditis elegans ~ 1000 cells/adults Can trace the lineage of every cell in its body Genome is sequenced

Fig. 18-8b

Round worms and humans

Molluscs

Common body plan Foot Visceral mass Mantle

Fig. 18-9a Visceral mass Coelom Kidney Mantle cavity Anus Heart Gill Foot Nerve cords Mouth Radula Shell Digestive tract Reproductive organs Radula Digestive tract Mouth

Fig. 18-9b Anus Mouth Larva = trocophore

Gastropods Bivalves Cephalopods

Gastropods Largest group “belly foot” Freshwater, salt water, terrestrial Most have single spiral shell Head with eyes on tips of tentacles

Bivalves Shells divided in 2 halves Mostly suspension feeders Mucous coated gills trap food Mostly sedentary

Cephalopods “head foot” In most shell is small and internal or missing Beak like jaw and radula Large brains, sophisticated sense organs

Annelids Segmented worms 3 main groups: Earthworms and relatives Polychaetes Leeches

Fig a Anus Segment wall Mucus-secreting organ Brain Dorsal blood vessel Coelom Digestive tract Mouth Pumping segmental vessels Nerve cord Ventral blood vessel Segment wall Excretory organ Nerve cord Bristles Intestine Dorsal blood vessel Longitudinal muscle Ventral blood vessel Bristles Excretory organ Circular muscle Epidermis Segment wall (partition between segments) Giant Australian earthworm

Earthworms Hermaphrodites Closed circulatory system Ventral nerve cord Complete digestive tract

Polychaetes “many hair” Use chaetae to swim, move, breath Mostly marine Some colonial

Leeches Some Bloodsuckers Mostly free-living carnivores Mostly live in freshwater, some marine, few terrestrial Bloodsuckers produce an anesthetic and anti-coagulant

Arthropods Most successful animal phylum Segmented Jointed appendages Exoskeleton

Fig a Cephalothorax Abdomen HeadThorax Antennae (sensory reception) Swimming appendages Pincer (defense) Mouthparts (feeding) Walking legs

Open circulatory system Variety of gas exchange organs

4 major lineages Chelicerates Millipedes and Centipedes Crustaceans Insects

Chelicerates

Fig c A scorpion (about 8 cm long) A black widow spider (about 1 cm wide) A dust mite (about 420  m long)

Millipedes and Centipedes

Crustaceans

Insects Segmented body Exoskeleton Jointed appendages Flight Waterproof cuticle Complex life cycle Many with short generations and large # of offspring

Complex life cycle Metamorphosis Regal moth

Head Thorax Abdomen Antenna Forewing Eye Mouthparts Hindwing Modular Body Plan