Comparing
Evolutionary Trends in
Invertebrates and
Vertebrates
(Chapters 29 + 33)
Body Symmetry
 Radial symmetry: extends from the center
outwards
 Ex:
 Bilateral symmetry: sides are like mirror
images (left and right)
 Ex:
Nervous System
(Response)
 Cephalization: concentration of sense
organs and nerve cells in front (top) of the
body
 Evolution from ganglia (simple) to brain
(complex)
Body Cavity
 coelom: area of body cavity between the
body wall and the digestive cavity
 Acoelomate: animal that lacks a body
cavity
 Ex: flatworm (planaria)
 Pseudocoelomate: animal that has a partial
body cavity
 Ex: roundworm (earthworm)
Embryo Development
 Depends on what the blastopore develops
into first…
 Protostome: mouth develops first
 Ex: invertebrates
 Deuterostome: anus develops first
 Ex: humans
Feeding and Digestion
 Intracellular digestion: digestion occurs
inside the cells
 Ex: sponges
 Extracellular digestion: digestion occurs
outside the cells in the digestive tract
 Ex: arthropods
Respiration (“Breathing”)
 Gills: feathery structures that take in O2 from
the water- usually close to the body surface
 Ex: fish
 Alveoli: tiny air sacs at the end of the
bronchiole that increase surface area and
act in gas exchange
 Ex: humans
Vertebrate Introduction
 Notochord: long supporting rod that runs
below the nerve cord
 Chordate: organism that has a dorsal nerve
cord
Circulatory System
 Open system: blood is not always in vessels
 Ex: insects, clams
 Closed system: blood always in vessels
 Ex: humans
Excretion
 Roles:
 control the output of waste products
 Involved in water balance
Movement and Support
 Hydrostatic skeleton: move with water-filled
cavity and accessory muscles
 Ex: jellyfish
 Exoskeleton: external skeleton on outside of
body
 Ex: insects
 Endoskeleton: internal skeleton on inside of body
 Ex: kangaroo
Reproduction
 External fertilization: eggs fertilized outside the
body (ex: coral)
 Internal fertilization: eggs fertilized inside the
body (ex: humans)
 Oviparous: eggs develop outside the mother
(ex: snake)
 Ovoviparous: embryo gets nutrients from the
yolk of egg (ex: seahorses)
 Viviparous: embryo gets nutrients from mom (ex:
humans)
Regulating Body Temp.
 Ectotherm: body temp determined by
environment- organism must
 Ex: lizards
 Endotherm: body temp controlled internally
 Ex: dogs
Reproductive Strategies
 K selection: having only a few offspring
but investing a lot of parental care into
them
Ex: humans, gorillas
 Occurs in crowded, competitive
populations

 r selection: having many offspring but
investing very little parental care
Ex: carp fish
 Occurs in populations that grow and
change rapidly
