Chapter 16: Phylum Mollusca

Question 1

What are the four types of food acquiring capabilities of those that fall under the phylum Mollusca?

Answer 1

• herbivorous grazers
• predaceous carnivores
• filter feeders
• parasites

Question 2

Majority of those in phylum mollusca live in what kind of environment? What are the other two not as common environments ?

Answer 2

• marine
• terrestrial
• fresh water aquatic

Question 3

Are Organisms belonging to phylum Mollusca protosomes or deuterostomes

Answer 3

• protosomes ( mouth first, anus second)

Question 4

The body plan of a Mollusc is divided into what two parts?

Answer 4

• head foot region

- visceral mass

Question 5

What is included in the head-foot portion of the Mollusc?(3)

Answer 5

• feeding, cephalic sensory and locomotor organs

Question 6

What is included in the visceral portion of a Mollusc ?(4)

Answer 6

• digestive, circulatory, respiratory and reproductive organs.

Question 7

Explain what the mantle cavity is?

• what makes up the mantle?
• whats the space between the mantle and body wall?
• The space contains what? (2)
• The mantle secretes what?

Answer 7

• two folds of skin form protective mantle
• mantle cavity
• gills (ctenidia) or a lung
• shell over the visceral mass

Question 8

Head- Foot region:

• Mollusc’s have a well developed head bearing what? (2)
• Photosensory receptors range from?
• what may be present but not always?
• Posterior to the mouth is the chief locomotor organ called the?

Answer 8

• mouth and some sensory organs
• simple to complex eyes
• tentacles
• the foot

Question 9

Radula?

• Is this specific to Mollusc’s or not?
• In the mollusca phylum this is present in all organisms except what?
• Describe the organ? Physical characteristics
• Functions? In regards to prey and the digestive tract

Answer 9

• specific to molluscs
• all except bivalves
• protruding , rasping, tongue like organ
• ribbon like membrane contains rows of tiny teeth
• it rasps particles of food off surfaces
• moves particles to digestive tract
• teeth that are very worn out are replaced
• pattern and number of teeth help in classification
• some are specialized to bore through hard material or harpoon prey

Question 10

Characteristics of the Foot:

• it’s usually located how? Ventral or Dorsal?
• It functions in what two basic concepts?
• What Are the modifications it has for varying organisms ? (3)
• Secreted mucus aids in what two things?
• Snails and bivalves do what to extend the foot?
• Burrowers extend the foot into what and do what?
• Free swimming forms have a modified the foot into what?

Answer 10

• ventral
• locomotion or substrate attachment
• A) attachment disc of limpets
  B) hatchet foot of clams
  C) siphon jet of squids
• locomotion allowing it to glide across the substrate via cilia OR in adhesion
• extend the foot hydraulically via engorgement of blood
• extend it into mud or sand, enlarge the tip as an anchor and draw forward
• into a wing or fin like swimming agents

Question 11

Mantle and Mantle Cavity Characteristics:

• The mantle is a sheath tissue located where?and secretes what when present?
• Mantle cavity : houses what that develop from what?
• The exposed surface of the mantle functions in what?
• In aquatic molluscs continuous flow of water does what? (3)
• Products of what three systems empty into the mantle cavity?

Answer 11

• on each lateral side
  L> secretes the shell when present
• houses the gills or lungs that develop from the mantle
• gaseous exchange
• brings in oxygen, good and flushes out wastes
• Digestive, excretory and reproductive systems

Question 12

Cephalopods use the head and mantle to create what?

Answer 12

• jet propulsion

Question 13

Describe the mollusc gill?

• filaments?
• countercurrent blood movement?
• In most molluscs there are how many and form what?

Answer 13

• has leaf like filaments - cilia propel water across the surface
• countercurrent (blood moves one way and water in the other ) blood movement in gill absorbs oxygen efficiently
• In most molluscs two ctenidia on opposite sides form an incurrent and excurrent chambers

Question 14

Describe the characteristics of the Shell:

• If present it has been secreted and lined by what?
• Periostracum is located where and is composed of what?
• Middle prismatic layer?
• Inner Nacreous layer?
• A thick periostracum for fresh water molluscs protects them against what??

Answer 14

• mantle
• outer horny layer
  L> composed of conchiolin, a tanned protein
• closely packed prisms of calcium carbonate
• next to the mantle, the nacre is laid down in thin layers
• acid from leaf decay in streams

Question 15

Describe the formation of a pearl?

Answer 15

• dirt gets into the outer mantle epithelium and is passed down slowly pushing through the mantle
• protects them against irritation via foreign material

Question 16

Why do fresh water molluscs have a thicker periostracum?

Answer 16

• protects them against acid water due to leaf litter in water

Question 17

What kind of circulatory system do they have? What is it comprised of?

Answer 17

• open circulatory system

- pumping heart, blood vessels and blood sinuses

Question 18

What class does not have a open circulatory system?

Answer 18

• cephalopods

- heart , vessels and capillaries

Question 19

Most molluscs have a pair of ____ also called metanephridia

The ___ ducts also discharge what?

Answer 19

• kidneys

- kidney, sperm and eggs

Question 20

What is the nervous system comprised of and is also very simpler in comparison to what other phylum?
- In air breathing snails the nervous system produces what hormones?
Within the phylum Mollusca what organisms do not have a simple nervous system ?

Answer 20

• pairs of ganglia
• annelids
• growth hormones
• squids/octopus aka Cephalopoda

Question 21

Reproduction and Life History:

• Most organisms in this group are what? Monoecious or Dioecious?Some may possibly be what as well?
• Eggs hatch and produce what? This units them with what other phylum?
• Larva undergoes what process producing a small juvenile chiton?
• In many gastropods and bivalves there is an intermediate larval stage which is called what?

Answer 21

• dioecious but some may be hermaphroditic
• free swimming trochophores, uniting them to annelids and marine turbellarians
• direct metamorphosis
• Veliger

Question 22

Molluscs are true ______ animals. They are ____ coelomates. They have ___ cleavage. They undergo determinate development which means what? Are they protosomes or deuterostomes?

Answer 22

• coelomate, schizocoelous, spiral
  L> Fate of the blastopore is determined very early in development
• Protosomes meaning the mouth forms from the blastopore