|
• Mollusks contain a true body cavity, or coelom, within the embryonic mesoderm and were among the first coelomate animals.
• The mollusks constitute the second largest phylum of animals in terms of named species. Their body plan consists of distinct parts: a head, a visceral mass, and a foot.
• Of the seven classes of mollusks, the gastropods (snails and slugs), bivalves (clams and scallops), and cephalopods (octopuses, squids, and nautilus), are best known.
• Gastropods typically live in a hard shell. During development, one side of the embryo grows more rapidly than the other, producing a characteristic twisting of the visceral mass.
• Members of the class Bivalvia have two shells hinged together dorsally and a wedge-shaped foot. They lack distinct heads and radulas. Most bivalves are filter-feeders.
• Octopuses and other cephalopods are efficient and often large predators. They possess well-developed brains and are the most intelligent invertebrates.
|
|
1. What is the basic body plan of a mollusk? Where is the mantle located? Why is it important in the mollusks? What occurs in the mantle cavity of aquatic mollusks?
2. What is a radula? Do all classes of mollusks possess this structure? How is it used in different types of mollusks?
3. How does the mollusk excretory structure work? Why is it better than the flame cells of acoelomates?
4. What is a trochophore? What is a veliger?
5. Do bivalves generally disperse as larvae or adults? Explain.
|
|
|
|
• Segmentation is a characteristic seen only in coelomate animals at the annelid evolutionary level and above. Segmentation, or the repetition of body regions, greatly facilitates the development of specialized regions of the body.
• Annelids are worms with bodies composed of numerous
similar segments, each with its own circulatory, excretory, and neural
elements, and array of setae. There are three classes of annelids, the
largely marine Polychaeta, the largely terrestrial Oligochaeta, and the
largely freshwater Hirudinea.
|
|
6. What evolutionary advantages does segmentation confer upon an organism?
7. What are annelid setae? What function do they serve? What are parapodia? What class of annelids possess them?
8. How do earthworms obtain their nutrients? What sensory structures do earthworms possess? How do these animals reproduce?
|
|
|
|
• The lophophorates consist of three phyla of marine animals-Phoronida, Ectoprocta, and Brachiopoda-characterized by a circular or U-shaped ridge, the lophophore, around the mouth.
• Some lophophorates have characteristics like protostomes,
others like deuterostomes. All are characterized by a lophophore and are
thought to share a common ancestor.
|
|
9. What prominent feature characterizes the lophophorate animals? What are the functions of this feature?
|
|
|
