Transcript Animals with a body cavity lying between the digestive tract and

Animal Kingdom
Animals…
• Animal life cycles include a period of embryonic
development. Three germ tissue layers called
ectoderm, endoderm, and mesoderm (present in
most species) give rise to adult organs.
• Animals with backbones are vertebrates. Animals
without a backbone are invertebrates. Body
symmetry, degree of cephalization, type of gut, type
of body cavity, and presence or absence of
segmentation are key characteristics in invertebrate
evolution and in distinguishing the different groups.
Vertebrates vs Invertebrates
• Humans have characteristics that can be traced back
millions of years to the invertebrates. Invertebrate
animals are not primitive and evolutionarily stunted,
but rather display adaptations to an amazing variety
of environments.
• Most animals have the following characteristics:
• multicellular,
• heterotrophic,
• aerobic,
• reproduce sexually (and perhaps asexually),
• develop from embryos,
• and are motile at some point in their life cycle.
Levels of organization in
multicellular organisms
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Cell- least inclusive
Tissue
Organ
Organ system
Organism- most inclusive
Body Symmetry and Cephalization
• Animals show either radial (round) or
bilateral (left and right sides) symmetry.
Bilateral animals also show anterior (head
end), posterior (tail end), dorsal (back), and
ventral (belly) orientations.
• As illustrated in this evolutionary lineage,
radial and bilateral symmetry led to two
major lineages of invertebrates.
• Cephalization means having a definite head
end, usually with feeding and sensory
features.
4 Directions
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Anterior
Posterior
Dorsal
Ventral
Type of Gut
The gut is the region where food is
digested and then absorbed. Some guts
are saclike with one opening for taking in
food and expelling waste. "Complete"
digestive tracts have two openings (mouth
and anus) for continuous food processing,
often through specialized regions.
Body Cavities
• A coelom (lined with peritoneum) is a space between
the gut and body wall that allows internal organs to
expand and operate freely. A peritoneum is a smooth
transparent membrane that lines the abdomen and
doubles back over the surfaces of the internal
organs to form a continuous sac.
• Some animals (flatworms or Platyhelminthes) are
acoelomate. They do not have a coelom but are
packed solidly with tissue.
• Others, such as roundworms (Nematoda), have a
"false" coelom or pseudocoel, not lined with
peritoneum.
• This animation (no audio) reviews the types of body
cavities.
Coeloms
• Acoelomate: Animals without a body cavity.
• Coelomate: Animals with a body cavity lying
between the digestive tract and body wall
that is completely lined with mesoderm (True
body cavity).
• Pseudocoelomate: Animals with a body
cavity lying between the digestive tract and
body wall that is incompletely lined with
mesoderm (False body cavity).
Segmentation
A segmented animal is composed of
repeating body units. The units may or
may not be similar to one another.
Earthworms would be a familiar
example in which the segments appear
similar. The segments may also be
grouped and modified for specialized
tasks, as they are in insects.
1 opening or 2
• Deuterostomes: Group of coelomate animals in
which the blastopore is associated with the
anus, a second opening is associated with the
mouth.
• Proterostomes: Group of coelomate animals in
which the blastopore is associated with the
mouth
3 skins!!
• def. Ectoderm: In animal embryos, the outermost
primary tissue layer that gives rise to the nervous system
and the outer layer of the integument.
• def. Endoderm: In animal embryos, the innermost
primary tissue layer that gives rise to the linings of the
digestive tract and associated structures.
def. Mesoderm: In animal embryos, the middle primary
tissue layer that gives rise to muscles, connective tissue
layers (e.g., lining the body cavity), and several internal
organs.