Animal Evolution – Animal Evolution – The InvertebratesThe Invertebrates

Characteristics of Animals

• Multicelled heterotrophic eukaryotes

• Require O2 for respiration

• Sexual & perhaps asexual reproduction

• Motile at some stage

• Develop from embryos

Here’s Something New:Symmetry!

RadialRadial BilateralBilateral

The Gut

• Region where food is digested and then absorbed

• Saclike gut– One opening for taking in food and expelling

waste

• Complete digestive system– Opening at both ends; mouth and anus

Body Cavities – Acoelomate (no coelom)

epidermisgut cavity

no body cavity; region between gut and body wall packed with organs

Body Cavities – Pseudocoel (false coelom)

epidermis gut cavity

unlined body cavity (pseudocoel) around gut

Body Cavities - Coelom

gut cavity

peritoneumlined body cavity (coelom)

Segmentation

• Repeating series of body units

• Units may or may not be similar to one another

• Earthworms - segments appear similar

• Insects - segments may be fused and/or have specialized functions

Animal Origins

• Originated during the Precambrian

(1.2 billion - 670 million years ago)

• From what? Two hypotheses:

– Multinucleated ciliate became

compartmentalized

– Cells in a colonial flagellate became

specialized

Sponges

• No symmetry

• No tissues

• No organs

• Reproduce sexually

• Microscopic

swimming-larval

stage

Nematocyst before triggering

After triggering, nematocyst pierces prey

Cnidarians (jellyfish)• Only animals that

produce nematocysts (stinging cells)

• Nerve net

• Hydrostatic skeleton

• Saclike gut

Flatworms

• Acoelomate, bilateral, cephalized animals

• All have simple or complex organ systems

• Most are hermaphrodites

Three Classes

Turbellarians (planarians)

pharynx

FlukesFlukes

TapewormsTapeworms

• Segmented worms

• Have digestive,

nervous,

excretory,

and

circulatory systems

Annelids

Polychaetes (Bristleworms)

• Most are marine

• Bristles extend from paired, fleshy parapods on each segment

• Head end is specialized

• Predators and parasites

• Less obvious body segmentation

• Most have sharp jaws

Leeches

• Bilateral, soft-bodied coelomate

• Most have a shell

• Mantle drapes over body and secretes shell

• Most have a fleshy foot

• Many have a radula for shredding food

Mollusks

• Gastropods

• Bivalves

• Cephalopods

Molluscan Diversity

Cephalopods

• Only the nautilus retains external shell

• Other cephalopods are streamlined, active swimmers

• All move by jet propulsion– Water is forced out of mantle cavity through a

funnel-shaped siphon

• Have large brains relative to body size

Cuttlefish Body Plan

• Closed circulatory system with heart and accessory heart

anus

siphon

gill heartaccessory heart

shell

brain

reproductive organ

stomachdigestive glandradula

Roundworms

• False coelom• Complete digestive system

gonadpharynx intestine

false coelom

eggs in uterus anus

muscularized body wall

• The phylum with the greatest number of species

• Four lineages:– Trilobites (all extinct)

– Crustaceans (crabs, shrimps, barnacles)

– Chelicerates (spiders, mites, scorpions)

– Uniramians (insects, centipedes, millipedes)

Arthropods

Adaptations for Success

• Hardened exoskeleton

• Jointed appendages

• Fused and modified segments

• Respiratory structures

• Specialized sensory structures

• Division of labor

• Most are marine, some freshwater, a few terrestrial

• Head has two pairs of

antenna, three pairs

of food-handling

appendages

Crustaceans

Copepods

Crayfish

Barnacles

Lobsters

Shrimps

Crabs

Isopods (pillbugs)

Crab Life Cycle

Larval and juvenile stages molt repeatedly and grow in size

• Originated in seas

• A few are still marine: horseshoe crabs, sea spiders

• The arachnids are all terrestrial

Spiders Mites

Scorpions Chiggers

“Daddy longlegs” Ticks

Chelicerates

Insect Diversity

• Insects are the only winged invertebrates

• There are more than 800,000 known species

• Most successful species are small in size and have a great reproductive capacity

Insect Body Plan

• Thorax usually has three pairs of legs and one or two pairs of wings

• Abdomen contains most internal organs and specialized structure for reproduction

• Three-part gut

• Malpighian tubules attach to midgut and

serve in elimination of wastes

Insect Headparts

antenna labrum

palpsmaxilla

labium

mandible

Grasshopper

Butterfly

Fly

Mosquito

adult

adult

adult

youngegg

nymphsegg

larvaeegg

Growth and molting

Incomplete metamorphosis

Complete metamorphosis

Types ofInsect

Development

Echinoderms

• Deuterostomes

• Almost all are marine

• Body wall has spines or plates of calcium

carbonate

• No brain

• Adults are radial with bilateral features

Echinoderm Diversity

• Crinoids (sea lilies and feather stars)

• Sea stars

• Brittle stars

• Sea urchins, heart urchins, sand dollars

• Sea cucumbers

Water Vascular System: Sea Star

sieve plate

ring canal

ampulla

part of the water-vascular system

Animal Evolution – The Vertebrates

Chapter 23

Chordates

• Most are coelomate, bilateral animals

• All share four features:– Notochord supports body

– Nervous system develops from dorsal nerve cord

– Embryos have pharynx with slits

– Embryos have tail that extends past anus

Lancelet Body Plan

NOTOCHORD

PHARYNX WITH GILL SLITS

TAIL EXTENDING PAST ANUS

DORSAL, TUBULAR NERVE CORD

Invertebrate Chordates

• Many of the animals that preceded

vertebrates were like the simplest

chordates – the urochordates

– Sea squirts

– Other tunicates

Larval Form of a Sea Squirt

nerve cord

gut

notochord

Adult Tunicate pharynx

with gill slits

oral opening (water in)

atrial opening (water out)

Cephalochordates

• Lancelets

• Fish-shaped filter feeders that lie buried in sediments

• Chordate characteristics of adult:– Notochord lies under dorsal nerve cord– Pharynx has gill slits– Tail extends past anus

Hagfish Body Plan

tentacles gill slits (twelve pairs) mucus glands

Trends in the Evolution of Vertebrates

• Shift from notochord to vertebral column

• Nerve cord expanded into brain

• Evolution of jaws

• Paired fins evolved, gave rise to limbs

• Gills evolved, gave rise to lungs

Craniates

• Cranium is a chamber of cartilage or bone that encloses all or part of a brain

• First craniates evolved by 530 million years ago

Evolution of Jaws

• First fishes

lacked jaws

• Jaws are

modifications of

the anterior gill

supports

supporting structures for gill slits

gill slits

jaw, derived from support structure

spiracle (modified gill slit)

jaw support

jaw

tunicates lancelets hagfishes lampreys

cartilaginous fishes

ray-finned fishes

lobe-finned fishes

lungfishes amphibians “reptiles” birds mammals

lungs or swim bladder

amniotes

tetrapods

jawed vertebratesvertebrates

craniatesancestral chordates

Evolution of Fishes

Jawed Fishes

• Most diverse and numerous group of

vertebrates

• Two classes:

– Cartilaginous fishes

– Bony fishes

Cartilaginous Fishes

• Most are marine predators

• Cartilaginous skeleton

• Main groups:

– Skates and rays

– Sharks

– Chimaeras (ratfishes)

caudal fin

dorsal fins

pectoral fin (pair)

pelvic fin (pair)anal fin

Bony Fishes

• Includes 96 percent

of living fish species

• Three subclasses:

– Ray-finned fishes

– Lobe-finned fishes

– Lung fishes