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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