BIOL 2112 Chapter Notes - Chapter 18: Bivalvia, Mollusca, Leech
4 Jun 2018
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V 1.Describe the defining characteristics of animals.
Animals are Eukaryotes, are multicellular heterotrophs, and have cells that
lack cell walls. They also use ingestion to eat food.
Most animals are diploid and reproduce sexually
2.Describe the general animal life cycle and the basic animal body plan.
life cycle:
blastula-a hollow ball of cells
gastrula-one side of the blastula folds in forming this stage
larval stage-an immature individual that looks different than that of an adult
body plan:
symmetry:
radial-circular
bilateral- distinct right and left sides
development:
protostome- first opening is the mouth
deuterostome- first opening is anus, second opening is the mouth
three tissue layers
endoderm-inner layer, ectoderm- outer layer, mesoderm- middle layer
3.Describe the Cambrian “explosion” of animal diversity and two hypotheses that
have been advanced to explain its occurrence.
The Cambrian explosion may have been caused by increasingly complex
predator-prey relationships or an increase in atmospheric oxygen.
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– Ecological causes: The evolution of hard body coverings led to
increasingly complex predator-prey relationships and diverse adaptations for
feeding, motility, and protection
– Geological causes: Atmospheric oxygen reached a high enough
concentration to support the metabolism of more active, mobile animals
– Genetic causes: The genetic framework for complex bodies was already in
place in the Hox complex of regulatory genes; variation in these genes
produced animal diversity
4.Characterize the nine animal phyla discussed in this chapter in terms of the
following traits:
Sponges (Phylum Porifera)
doesn’t have true tissues/ no germ layers
lacks body symmetry/ asymmetrical
usually marine
reproduce asexually
hermaphrodite
digestive functions- choanocytes
circulatory functions- amoebocytes
Cnidarians (Phylum Cnidaria)
radial symmetry
has two tissue layers
outer epidermis- ectoderm- nerve net and
cnidocytes(specialized cells that release nematocysts)
inner cell layer lining the digestive cavity
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Flatworms (Phylum Platyhelminthes)
are bilaterians
has three tissue layers
lacks a body cavity- Acoelomates
digestive gut
excretory system(flame cells)
hermaphrodite
free living(planarians)
parasitic ( fluke and tapeworm)
Nematodes or Roundworms (Phylum Nematoda)
bilateral symmetry
three tissue layers
has cuticle (prevents body from drying out)
has a complete digestive tract (has mouth and anus)
dioecious (separate male and female)
molting (shed their cuticle to grow)
pseudocoelomates
Molluscs (Phylum Mollusca)
has muscular foot (used for locomotion)
visceral mass (contains internal organs), mantle (secretes a shell that
encloses organs), circulatory system (pumps blood throughout the body)
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Document Summary
Animals are eukaryotes, are multicellular heterotrophs, and have cells that lack cell walls. 3. describe the cambrian explosion of animal diversity and two hypotheses that have been advanced to explain its occurrence. The cambrian explosion may have been caused by increasingly complex predator-prey relationships or an increase in atmospheric oxygen. Ecological causes: the evolution of hard body coverings led to increasingly complex predator-prey relationships and diverse adaptations for feeding, motility, and protection. Geological causes: atmospheric oxygen reached a high enough concentration to support the metabolism of more active, mobile animals. Genetic causes: the genetic framework for complex bodies was already in place in the hox complex of regulatory genes; variation in these genes produced animal diversity. 4. characterize the nine animal phyla discussed in this chapter in terms of the following traits: Sponges (phylum porifera) doesn"t have true tissues/ no germ layers lacks body symmetry/ asymmetrical usually marine reproduce asexually hermaphrodite digestive functions- choanocytes circulatory functions- amoebocytes.
