Difference between revisions of "AY Honors/Shells - Advanced/Answer Key"
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===d. Movements=== | ===d. Movements=== | ||
===e. Securing food=== | ===e. Securing food=== | ||
| − | Bivalves are unique among the molluscs for lacking a radula; they feed by siphoning and filtering large particles from water. | + | '''Bivalves''' are unique among the molluscs for lacking a radula; they feed by siphoning and filtering large particles from water. |
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| + | '''Univalves''' include some that are herbivores, detritus feeders, predatory carnivores, scavengers, parasites, and also a few ciliary feeders, in which the radula is reduced or absent. | ||
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| + | The radula of a univalve is usually adapted to the food that a species eats. The simplest univalves are the limpets and abalones, herbivores that use their hard radulas to rasp at seaweeds on rocks. | ||
| + | |||
| + | Many marine univalves are burrowers, and have soft siphons or tubes that extend from the mantle. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw a small flow of water into their bodies. The siphon is used primarily to "taste" the water, in order to detect prey from a distance. Univalves with siphons tend to be either predators or scavengers. | ||
===f. Self-preservation=== | ===f. Self-preservation=== | ||
Revision as of 22:15, 2 August 2008
1. Have the Shell Honor.
2. Define the term "mollusca" or "mollusk."
The word mollusc is derived from the French mollusque, which originated from the Latin molluscus, meaning thin-shelled, from mollis, soft
The body of a mollusk consists of three sections; a head, with eyes or tentacles; a muscular foot; and a visceral mass housing the organs.
3. Learn the classification terms of mollusks, know the distinguishing characteristics of each, and become acquainted with several species under each class.
There are ten classes of molluscs; eight of the classes have living representatives, the other two classes are known only from fossils. More than 250,000 species of mollusc are recognized and named. Snails (Gastropoda) account for about 80% of living mollusc diversity.
| Class | Major organisms | Extant species | Distribution |
| Caudofoveata | worm-like organisms | 70 | deep ocean |
| Aplacophora | solenogasters, worm-like organisms | 250 | deep ocean |
| Polyplacophora | chitons | 600 | rocky marine shorelines |
| Monoplacophora | limpet-like organisms | 11 | deep ocean |
| Gastropoda | abalone, limpets, conch, nudibranchs, sea hares, sea butterfly, snails, slugs | 150,000& | marine, freshwater, land |
| Cephalopoda | squid, octopus, cuttlefish, nautilus | 786 | marine |
| Bivalvia | clams, oysters, scallops, mussels | 8000 | marine, freshwater |
| Scaphopoda | tusk shells | 350 | marine |
| Rostroconchia † | fossils; probable ancestors of bivalves | extinct | — |
| Helcionelloida † | fossils; snail-like organisms such as Latouchella | extinct | — |
4 Distinguish between univalve and bivalve mollusks from the following considerations:
a. Shell
The terms univalve and bivalve refer to the configuration of the shells of the mollusks. Univalves, such as snails, have shells consisting of one (thus uni-) piece. Bivalves, such as mussels, have shells consisting of two (thus bi-) pieces hinged together.
b. Mollusk body
Univalve bodies could almost be described as folded such that the mouth and anus both appear the the shell's opening. Bivalves on the other hand have flattened bodies.
c. Reproduction
All land snails are hermaphrodites, producing both spermatozoa and ova. In other words, each individual is both male and female. Some freshwater snails, such as Apple Snails, and marine species, such as periwinkles, have separate sexes; they are male and female. Most snails can mate when they are around 1 year old.
Prior to reproduction, most land snails perform a ritual courtship before mating. This may last anywhere between two and twelve hours. Prolific breeders, pulmonate land snails inseminate each other in pairs to internally fertilize their ova. Each brood may consist of up to 100 eggs.
Pulmonate land snails and slugs have a reproductive opening on one side of the body, near the front, through which the outer reproductive organs are extruded so that exchange of sperm can take place. After this, fertilization occurs and the eggs develop.
Garden snails bury their eggs in shallow topsoil primarily while the weather is warm and damp, usually 5 to 10 cm down, digging with their foot. Egg sizes differ between species, from a 3 mm diameter in the grove snail to a 6 cm diameter in the Giant African Land Snail. After 2 to 4 weeks of favorable weather, these eggs hatch and the young emerge. Snails may lay eggs as often as once a month.
In bivalves, the sexes are usually separate, but some hermaphroditism is known. Bivalves practice external fertilization. External fertilization is a form of fertilization in which a zilo cell is united with an egg cell external to the body of the female. Thus, the fertilization is said to occur "externally". This is distinct from internal fertilization where the union of the egg and sperm occur inside the female after insemination through copulation.
In sexual reproduction, there must be some way of getting the sperm to the egg. Since sperm are designed to be mobile in a watery environment, aquatic mollusks can make use of the water in which they live. Eggs and sperm are simultaneously shed into the water, and the sperm swim through the water to fertilize the egg in a process known as broadcast fertilization.
d. Movements
e. Securing food
Bivalves are unique among the molluscs for lacking a radula; they feed by siphoning and filtering large particles from water.
Univalves include some that are herbivores, detritus feeders, predatory carnivores, scavengers, parasites, and also a few ciliary feeders, in which the radula is reduced or absent.
The radula of a univalve is usually adapted to the food that a species eats. The simplest univalves are the limpets and abalones, herbivores that use their hard radulas to rasp at seaweeds on rocks.
Many marine univalves are burrowers, and have soft siphons or tubes that extend from the mantle. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw a small flow of water into their bodies. The siphon is used primarily to "taste" the water, in order to detect prey from a distance. Univalves with siphons tend to be either predators or scavengers.
f. Self-preservation
5. Identify from shells or drawings and know the meaning of the following concho logical terms:
a. Valve
b. Apex
c. Aperture
d. Byssus
e. Foot
f. Mantel
g. Operculum
h. Mother of pearl
i. Epidermis
j. Ribs
k. Teeth
l. Concentric lines
m. Canal
n. Spines
o. Whorls
p. Lips
6. Explain the development of a shell. How long do mollusks live?
7. Give some facts about the life of a strombus pugilis (fighting conch) and explain why this shell is so named.
8. Explain the activities of the shipworm.
Adventist Youth Honors Answer Book/Nature/Shipworm
9. What accounts for the distribution of mollusks.
10. Name two mollusks that have no shells.
Slug 
Octopus 
Cuttlefish 
Squid
11. Find answers for the following interesting questions:
a. How are bivalve and univalve animals fastened to their shells?
b. How is shell color controlled?
c. What mollusk has four gills?
d. From what sea animal was India ink formerly made?
e. What mollusk spins a silken thread?
f. What shells were used for money by ancient tribes?
g. What shell is considered sacred by the Tibetans?
h. Purple dye of ancient times came from the secretion of what mollusk?
i. What is the source of pearls? How are they formed?
12. Name six commercial uses for shells.
13. Do one of the following:
a. Personally find and collect 40 species of shells representing the five classifications. List each shell as to the place and date it was found, common name, scientific name, and class.
b. Make a collection of 50 species of shells you have found, received, or purchased representing the five classifications. List each shell collected as follows: if personally found, give the information called for under letter "a" above; if received or purchased, give the name of the person from whom the shell was received, the habitat of the shell, the date of its acquisition, and its common name, scientific name, and class.
References
- ↑ Ponder, Winston F. and Lindberg, David R. (Eds.) (2008) Phylogeny and Evolution of the Mollusca. Berkeley: University of California Press. 481 pp. ISBN 978-0520250925.
