Download Chapter 32: Animal Diversity

BY 124 SI – Exam II – Worksheet #2
Chapter 32: Animal Diversity
1. Reproduction / Development:
a. Can you outline the general mechanism of animal development, beginning with the parental egg/sperm
and ending with the gastrula? You should show these processes and their resulting products: fertilization,
cleavage, blastulation, and gastrulation.
Sperm fertilizes egg to form the zygote; zygote undergoes cleavage to form the 8-cell stage; 8-cell stage
undergoes blastulation to form the blastula; blastula undergoes gastrulation to form the gastrula
b. What are Hox genes, and why are they important?
While all eukaryotes have regulatory genes (many of which contain DNA sequences called homeoboxes),
animals share a unique homeobox-containing family of genes (called Hox genes), which are involved in
regulating gene expression in embryonic development; Hox genes control the expression of dozens or
even hundreds of other genes that influence animal morphology
2. Animal History: Can you list and describe the three hypotheses used to explain the Cambrian explosion?
1. Emergence of new predator-prey relationships – triggered various evolutionary adaptations
2. Accumulation of atmospheric oxygen – supported the active metabolisms of mobile & larger animals
3. Evolution of Hox complex – provided the developmental flexibility accounting for the diverse body
plans appearing during the Cambrian explosion
3. Animal Body Plans:
a. Symmetry: Can you list and describe the two types of body symmetry found in animals? How does an
animal’s body symmetry fit its lifestyle?
 Radial symmetry – body symmetry in which the body is shaped like a pie or barrel (lacking a left and a
right side); can be divided into mirror-image halves by any plane through its central axis; has a top side
and a bottom side, but lacks front & back ends and left & right sides
 Bilateral symmetry – body symmetry in which a central longitudinal plane divides the body into two
equal but opposite halves; has two axes of orientation: front to back and top to bottom; bilateral
animals have: anterior (front) & posterior (back) ends, dorsal (top) & ventral (bottom) sides, and left &
right sides
 Cephalization – an evolutionary trend toward the concentration of sensory equipment (brain) at the
anterior end of the body; many animals with bilateral symmetry
 An animal’s symmetry fits its lifestyle: many radial animals are sessile (attached to a substrate) or
planktonic (drift or weakly swim); bilateral animals move actively from place to place and most have a
central nervous system that enables them to coordinate complex movements (crawling, flying,
swimming, etc.)
b. Tissues: Can you list and describe the three germ layers produced by gastrulation? What structures arise
from each type of germ layer?
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Ectoderm – the outermost of the three primary germ layers in animal embryos; gives rise to the outer
covering and, in some phyla, the central nervous system
Endoderm – the innermost of the three primary germ layers in animal embryos; lines the archenteron
(developing digestive tube) and gives rise to the lining of the digestive tract (or cavity) and organs
such as the liver and lungs of vertebrates
Mesoderm – the middle primary germ layer in an animal embryo; develops into the notochord, the
lining of the coelom, muscles, skeleton, gonads, kidneys, and most of the circulatory system in
species that have these structures
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BY 124 SI – Exam II – Worksheet #2
c. Body Cavities: Can you list and describe the three triploblastic animal body cavity types?
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Coelomates – an animal that possesses a true coelom, a body cavity completely lined by tissue
derived from the mesoderm (Ex. Earthworms)
Pseudocoelomates – an animal whose body cavity is lined by tissue derived from the mesoderm
& endoderm (Ex. Roundworms)
Acoelomates – a solid-bodied animal lacking a cavity b/w the gut and outer body wall (Ex.
Planarians)
4. Protostomes & Deuterostomes: Can you complete this table?
Protostome Development
(molluscs, annelids, etc)
Cleavage: Spiral & Determinate
Solid masses of mesoderm
split and form coelom
Mouth develops from
Fate of the
blastopore (anus develops
Blastopore:
from a secondary opening)
Coelom Formation:
Deuterostome Development
(echinoderms, chordates, etc)
Developmental Phase
Radial & Indeterminate
Eight-cell stage
Folds of archenteron form
coelom
Anus develops from blastopore
(mouth develops from a
secondary opening)
Gastrula stage
Gastrula stage
Chapter 33: Invertebrates (Part 1)
SUBKINGDOM PARAZOA (Sponges only)
5. Phylum Porifera (Sponges): Can you identify and describe the anatomical structures found in sponges? (Label
the diagram) ANSWERS: (a.) OSCULUM, (b.) MESOHYL, (c.) SPONGOCOEL, (d.) CHOANOCYTE,
(e.) AMOEBOCYTE
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BY 124 SI – Exam II – Worksheet #2
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