Introduction
to Animals
To be an animal means
1. Multicellular –
humans have ~ 50 - 100 trillion cells
2. Ingestive heterotroph
3. Lacking a cell wall
4. Specialization of cells
(except Porifera)
5. May involve movement & sexual
reproduction (formation of a zygote)
Phylogenetic tree of animal kingdom
• Based on:
– Body symmetry
– Patterns of embryo development
– Comparing fossils
– rRNA
Symmetry
• Overall pattern of structure
– Asymmetric - No symmetry as with the Porifera
– Radial symmetry – even cut along a diameter.
Echinodermata and Cnidaria
– Bilateral symmetry – even cut along a central
plane. Worms, Arthropods, Mollusks,
Echinoderms, and Vertebrates
Trends in Animal Evolution
• As you go up the phylogenetic tree,
you will see a greater tendency towards
bilateral symmetry.
• Also a concentration of nerves
(sensory organs) towards the front of
the organisms known as cephalization
Body views
1.
2.
3.
4.
Dorsal – top/back
Ventral – belly/bottom
Anterior – front/head
Dorsal (top)
Posterior – tail/rear
Posterior (tail end)
Anterior (front)
Ventral (bottom)
Cleavage
• A series of cell divisions that occurs
immediately following fertilization
– Mitosis occurs but cells do not grow in size.
Stages in Cleavage
Blastula
Zygote
Morula
Gastrula
Indented
ball stage
Hollow ball stage
Solid ball stage
During gastrulation, an indentation occurs.
A multi-layer embryo is formed with 3 germ layers
Blastopore – opening of indentation
• Protostome
– Blastopore developes into the oral opening
(mouth)
– Mollusks, arthropods and annelids
• Deuterostomes
– Blastopore developes into anus
– Echinoderms and Chordates (that’s us)
Germ Layers
•
•
•
Fundamental tissue types found in embryos
of animals (but not sponges)
Gives rise to every body feature, organs &
tissues
2 germ layers in Cnidaria & 3 in all others
–
–
–
Endoderm – forms throat, gills, lungs and digestive
tract (with pancreas and liver)
Ectoderm – forms outer skin, hair, nails and
nervous system
Mesoderm – skeleton, muscles, inner skin layer,
circulatory system and lining of the body cavity
Body Cavities
•
•
•
Acoelomates – Body cavity is absent. As in Flatworms .
Endoderm is connected solidly to mesodermal tissue
Pseudocoelomates – Body cavity contains three distinct
layers but endoderm is not connected to mesoderm. Free
floating in fluid. Found in roundworms.
Coelomates – True body cavity. Mesoderm lines body
cavity while supporting endodermic. Mollusks, annelids,
arthropods, chordates and echinoderms
Systems through the Phyla
Circulatory systems
•
Closed Circulatory System
– One in which blood is always contained within a
vessel. Heart serves as a pump. Found in annelids,
chordates
Open Circulatory System
– Pumps blood into spaces around the body tissues.
From there the blood makes its way back to vessels
that will carry it back to the heart, or possibly to
holes in the heart itself. Found in Arthropods and
some mollusks
Skeletons
Exoskeleton – Rigid, outer
covering protecting soft
internal tissue. Found in
Arthropods and
mollusks. Needs to be
shed (molt) as animal
grows.
Endoskeleton – Internal
skeleton. Best for larger
organism. Found in
echinoderms and
vertebrates. Grows as
animal grows.
Reproduction:
•
•
Asexually by budding
(Porifera, Cnidarians) or
regeneration (Porifera,
Planaria, Sea stars)
Sexually
–
–
Hermaphroditic – contains
both sexes (but not self
fertilization necessarily).
Think of your earthworm
Separate sexes – as you
go up the phylogenetic
tree
Development
Incomplete
metamorphosis –
Direct development –
young animal is born
or hatched looking
like adult but smaller.
No larval stage.
Mantids,
Grasshoppers, us
Complete
metamorphosis –
Indirect development
– intermediate larval
stages appearing
different from adult.
Butterfly, flies, moths