Download Intro to Animals

Animals!
Introduction
What is an animal?
Structure, nutrition and life history
define animals…
–
While there are exceptions to nearly every criterion for
distinguishing an animal from other life forms, five criteria,
when taken together, create a reasonable definition.
1.
2.
3.
4.
5.
Multicellular, heterotrophic eukaryotes
No cell wall
Nervous and muscle tissue
Sexual reproduction, diploid dominant
Unique regulatory gene for development
1. Multicellular, heterotrophic
eukaryotes
•
They must take in preformed organic
molecules through ingestion, eating other
organisms or organic material that is
decomposing.
– They gotta eat!
2. No cell wall
• Animal cells lack the cell walls that provide
strong support in the bodies of plants and
fungi.
• The multicellular bodies of animals are held
together with the extracellular proteins,
especially collagen.
3. Nerves and
Muscles
• Animals have two unique types of tissues:
– nervous tissue for impulse conduction
– muscle tissue for movement
4. Sexual reproduction, diploid
stage dominates life cycle
• small flagellated sperm fertilizes a nonmotile egg
• zygote undergoes cleavage, a succession mitotic
cell divisions, leading to the formation of a
multicellular, hollow ball of cells called the blastula.
• During gastrulation, part of the embryo folds
inward, forming the blind pouch characteristic of the
gastrula
This produces two
tissue layers: the
endoderm as the
inner layer and the
ectoderm as the
outer layer.
5. Regulatory genes: Hox genes
• Hox genes: Regulatory genes that act in the
developing embryo to control the transformation of
a zygote to an animal of specific form
– regulate the expression of other genes
– contain common DNA sequences,
called homeoboxes
– All animals, from sponges to the most
complex insects and vertebrates have
Hox genes
– the number of Hox genes correlated
with complexity of the animal’s anatomy.
– variation in when and where the Hox genes are expressed in
a developing embryo provides the genetic basis for the great
diversity of animal forms that have evolved from a common
ancestor
Animal evolution
• The animal kingdom probably evolved from a
colonial, flagellated protist
• Ancestor lived over 700
million years ago in the
Precambrian era.
• probably related to
choanoflagellates
• Modern choanoflagellates
are tiny, stalked organisms
inhabiting shallow ponds,
lakes, and marine
environments
Phylogenetic
Tree of Animals
• Phylogeny is
changing due
discoveries in
molecular biology
• The traditional view
of relationships
among animal phyla
are based mainly on
key characteristics
of body plans and
embryonic
development.
• There are four main
branches…
1. Parazoa vs. Eumetazoa
•
Parazoa: lack true
tissues
– Phylum Pofifera:
sponges – unique
development and
structural simplicity
•
Eumetazoa: have true
tissues
– Tissues are a basic
feature of all other
animal phyla
2. Radial vs. Bilateral Symmetry
Eumetazoans divided based on body symmetry
Radiata: Radial Symmetry
•
phylum Cnidaria (hydras, jellies, sea anemones and their
relatives) and phylum Ctenophora (comb jellies)
•
Diploblastic: two germ layers - ectoderm, covers
surface of the embryo, endoderm, the innermost layer,
lines the developing digestive tube
Bilateria: Bilateral Symmetry
• Have a dorsal and ventral side, an anterior and
posterior end, and a left and right side.
• Cephalization: concentration of sensory equipment
on the anterior end (a brain!)
• Triploblastic: third germ layer, mesoderm lies
between the endoderm and ectoderm
– develops into the muscles and organs
3. Body Cavity
• Acoelomates: triploblastic animals with solid
bodies
– Do not have a cavity between the digestive tract
and outer body wall
– phylum Platyhelminthes
• Pseudocoelom: there is a body cavity, but it is
not completely lined with tissue derived from
the mesoderm.
– include the rotifers (phylum Rotifera) and the
roundworms (phylum Nematoda)
• Coelomates: organisms with a true coelom, a
fluid-filled body cavity completely lined by tissue
derived from the mesoderm.
– The inner and outer layers of tissue that surround
the cavity connect dorsally and ventrally to form
mesenteries, which suspend the internal organs.
Functions:
• cushions the
suspended organs
• hydrostatic skeleton
in some animals
• enables the internal
organs to grow and
move independently
to the outer body wall
4. Protostomes vs.
Deuterostomes
Coelomate phyla are divided based on
differences in their development.
Protostomes
• spiral cleavage: planes of cell
division are diagonal to the vertical
axis of the embryo
• Coelom formation begins in the
gastrula
• Blastopore forms the mouth
– The mollusks, annelids, arthropods
Deuterostomes
• radial cleavage: the cleavage
planes are parallel or
perpendicular to the vertical egg
axis
• Coelom forms from the
mesodermal outpocketings
• Blastopore forms the anus
– echinoderms, chordates (you!)