Chapter 16: Phylum Mollusca, Class - Gastropoda

Question 1

This class is the ___ and ___ group of Molluscs. It includes what five organisms?

Answer 1

• largest, diverse

- snails, slugs, whelks, conchs, periwinkles

Question 2

Habitat wise where do they live?

Answer 2

• marine forms, air breathing terrestrial forms (slugs and snails)

Question 3

They are typically sluggish ____ animals.

Answer 3

• sedentary

Question 4

What is their chief defence ?

Answer 4

shell

Question 5

What can some also do as a defence mechanism?

Answer 5

• produce distasteful or toxic secretions

Question 6

Many have an operculum which has what function?

Answer 6

• covers shell aperture when body is withdrawn

Question 7

Some can deliver a deadly blow with the ________ which has a sharp _____.

Answer 7

• muscular foot, operculum

Question 8

• Many serve as _______ hosts for parasitic worms.

Answer 8

• intermediate

Question 9

Torsion ????? brief description?

• contraction of a foot retractor muscle pulls ___ and ___ 90 degrees ____.
• Moves the anus to the ___ side of the body.
• Recent studies have shown that shell movement is ____ of visceral movement.

Answer 9

• developmental process that changes the relative position of the shell, digestive tract and anus, nerves that lie on both sides of the digestive tract and the mantle cavity containing the gills.
• shell and viscera, counterclockwise
• right
• independent

Question 10

Torsion Process?

• The first movements of the shell rotate it between ___ and __ degrees into a permanent position.
• The mantle cavity develops on the ___ side of the body near the ___ but it is initially ___ from it. -Anus and mantle cavity usually move further to the __ and the mantle cavity is remodelled to ____ the anus.
• The digestive tract moves both ___ and __ so that the anus lies above head within mantle cavity. —– -After torsion, anus and mantle cavity open above the __ and __.
• Certain viscera on the __ are now on the __ and vice versa.
• The nerve cord forms a ____ shape.
• Varying degrees of detorsion in ____ and ___ has been observed
• This arrangement resulting from torsion creates __. Which is what exactly?
• The developmental sequence is called what?

Answer 10

-90 and 180
- right side, anus, separate
- right, encompass
- laterally and dorsally
-mouth and head
-left , right
-figure eight
-opistobranches and pulmonates
-fouling (problematic)
L> wastes being washed back over the gills
- ontogenetic torsion

Question 11

What is coiling?

• occurs at the same larval stage as what? Do they share the same evolutionary origin?
• Planospiral shell?
• Conispiral shell?

Answer 11

• spiral winding of the shell and visceral mass
• torsion, no
• all whorls in a single plane, primitive state
• provides more compactness , each whorl is to the side of the previous

Question 12

Coiling causes the shifting of the shell __ and __ to help balance the ___ weight distribution. What three things are lost on the right side in most species? The loss of one of these things on the right is benefit- how so?

Answer 12

• upward and back
• uneven
• gill, auricle and kidney
• loss of the right gill provides one solution to the problem of fouling

Question 13

What are the three major groups of Gastropods?

Answer 13

• prosobranchs, opisthobranchs, pulmonates

Question 14

Prosobranchs :

• most are snails living in ___ and a few ___ and ___ ones.
• They have one pair of ?
• The sexes are usually ___.
• The ____ is often present .
• Give two examples?
• Species of ___ deliver a lethal sting to secure prey. The venom is a ___. Specific for the _____ of its preferred prey. What are it’s medical uses?

Answer 14

• marine, freshwater, terrestrial
• tentacles
• separate
• operculum
• Abalones and periwinkles
• Conus
• conotoxin
• neuroreceptors
• non addictive pain killer

Question 15

Opisthobranchs:

• Three examples?
• Nearly all of them are ___?
• A few are __
• Most live in which: deep/shallow water
• How many pairs of tentacles are found
• What is the status of it’s shell?
• The sexes are ?

Answer 15

• sea slugs, sea hares and nudibranches
• marine
• pelagic
• shallow
• 2
• absent or reduced
• monoecious

Question 16

Pulmonates:

• They are mostly ____ but some ___ snails and slugs.
• They lost _____ but the ___ serves as a ___.
• The sexes are?
• Aquatic forms have ___ set of tentacles which bear ___ while the terrestrial forms have ___ pairs of tentacles with one bearing ___.

Answer 16

• land and freshwater
• ctendia (gill), mantle
• monoecious
• one, eyes, two , eyes