Download Invertebrates

Invertebrates – Division of
Animals without Backbone
You are doing a survey of
invertebrate characteristics
with the graphic organizer
Evolutionary Trends in Invertebrates:
1. Tissue
• Two tissue layers  three tissue layers
• Tissue Specialization (Tissue Derminatization)
• Body Cavities: Acoelomates  Coelomates
2. Asymmetry  radial  bilateral
3. Protostomes  Deuterostomes
• Protostomes: Mouth from Blastopore
• Deuterostome: Anus from Blastopore
• Circulatory System
– Open  Closed circulatory system
– Heart-like Structures (like aortic arches)  Hearts
• Digestive System and Excretion
– One opening  Two openings
• Nervous System
– Trend to toward cephalization and centralized
nervous system that is “controlled” by brain
– More developed senses (Flatworms “Eyespot”
and Eyes)
– Stupid  Less Stupid
• Reproduction
–Asexual  Sexual
–External fertilization  Internal
Fertilization
Tissues
• A group of similar cells that work together
to carry out a job. There are four types of
tissue:
1. Connective
2. Muscle
3. Epithelial
4. Nervous
Symmetry
• There are four major types of
symmetry
–Asymmetry
–Spherical symmetry
–Radial symmetry
–Bilateral symmetry
Body Cavities
• Acoelemates like flatworms or jellyfish
• Pseudocoelemates like roundworms
• Coelomates like mollusks, arthropods,
and echinoderms
Coelomate Evolution body cavities that develops within the mesoderm
•
Dorsal
•
Cranial
(cephalization)
•
Spinal
•
Ventral
•
Thoracic
•
Abdominal
Invertebrate body plans
• Acoelomate with 2 germ layers
–without a coelom
–has endoderm
–has ectoderm
–Example – sponges and cnidarians
Acoelomates
• Have 3 germ layers
– No coelom
– Endoderm, ectoderm (1), mesoderm (2)
– Flatworms are an example
True Coelomates
• Have three tissue
layers
– Endoderm,
Mesoderm,
Ectoderm
• Have a coelom
within the
mesoderm
• You are one!
Comparative Body Plans
• Which do you
think is the most
primitive /
advanced?
• Why?
Further classification of Animals with
Coeloms is by embryonic development
TWO MAJOR LINEAGES
Protostomes or Deuterostomes
Protostomes
•
•
•
•
•
•
Blastopore becomes the mouth
Second opening becomes the anus
Coelom formed via schizocoely (cleavage)
Circulatory system primitively dorsal
Nervous system primitively ventral
Phyla Mollusca, Annelida, Arthropoda and
others
Coelom formed via schizocoely
Deuterostomes
•
•
•
•
•
•
Blastopore becomes the anus
Second opening becomes the mouth
Coelom formed via enterocoely
Circulatory system primitively ventral
Nervous system primitively dorsal
Phyla Echinodermata (starfish), Hemichordata
(sea feathers) and others
Coelom formed via enterocoely
Cephalization
• Consider the presence of Nervous
tissue in lower invertebrates.
• Do they have a brain?
• Are they able to respond to stimuli?
• The sponge has no nervous tissue at all
and thus no cephalization
• The cnidarians have a neural net but no
central processing location.
Cephalization
• Platyhelminthes is the
first with central
processing point
called a ganglia
(nervous inputs can be
gathered and
responded to). This is
an early “brain”.
• Cephalization tends to
occur at the anterior
end of the body.
Not all groups have cephalization. In fact, some have been
successful with a complete absence of cephalization. But, the
majority of successful animal groups have some degree of
cephalization.
Skeletal Systems
• Hydrostatic skeleton
• Exoskeleton
– Made of chitin
• Can become very heavy and limits the size that insects can
ultimately grow to.
• Endoskeleton
– Support, mineral storage and creates blood cells
Hydrostatic Skeleton
Exoskeleton
Endoskeleton
Integumentary –
Development of Skin Layer
• Protects against drying out which is extremely
significant as animals move onto land
• Keratin – protein found in skin that is a barrier
against the evaporation of water.
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