Mollusks

Question 1

Basic body plans of mollusks

Answer 1

Foot, mantle, shell, visceral mass, coelomate animals with bilateral symmetry

Question 2

Foot

Answer 2

Soft muscular, usually contains the mouth and feeding structures, also used for movement

Question 3

Mantle

Answer 3

• Membrane that surrounds the internal organs
  Thin, delicate tissue layer, covers most of the body

Question 4

Shell

Answer 4

Made of Calcium carbonate (CaCO3) secreted by glands in the mantle

Question 5

Visceral mass

Answer 5

Contains the internal organs

Question 6

Main classes of mollusks

Answer 6

Gastropoda, bivalve, cephalopoda

Question 7

Gastropoda

Answer 7

“Stomach-foot”
- Snails, slugs, abalone, sea butterflies, sea hares, and nudibranchs
- Most snails have a lid-like part called an operculum on the back of the foot so they can dry their bodies into their shell and close off the opening
- “Shell-less” varieties exhibit behaviours that protect them and/or have ink glands, poisonous chemicals in their skin, nematocysts, and bright “danger” colours

Question 8

Bivalvia

Answer 8

“two-shell”
- have 2 shells that can be tightly closed with strong muscles
- many burrow in mud/sand (clams) others have sticky threads to attach themselves to rocks (mussels)
- Mantle glands make CaCO3 that forms their shells, and mother of pearl to keep the inside walls of their shells smooth- pearls form when grain of sand/pebble gets between mantle&shell. Mother of pearl secreted to coat it to prevent further irritation

Question 9

Cephalopoda

Answer 9

“head-foot”
- Octopi, squid, cuttlefish, and nautiluses
- have tentacles with sucking disks, some also have arms
- travel via jet-propulsion by taking in water through their mantle, then shooting it out through their siphon

Question 10

Feeding of gastropods

Answer 10

Use a tongue shaped radula to scrape algae off of rocks/or eat land plant material (herbivore)/or drill holes in shells or their prey (carnivores)

Question 11

Radula

Answer 11

A tooth made of flexible skin, spread over a strong supporting rod of cartilage. Feels like sandpaper.
- Move the outer skin layer back and forth over the cartilage rod to feed
- Herbivore mollusks use radulas to scrape algae off rocks
- Carnivorous mollusks use radular to drill into other mollusks & feed on their internal body parts

Question 12

Feeding of cephalopods

Answer 12

Tend to be carnivorous, sharp jaws- “beak”
- Some also have poison/radula
- Tentacles used to catch & direct prey into their mouths

Question 13

Feeding of bivalves

Answer 13

Filter-feeders
- Use gills to sift food (ex. phytoplankton) from the water
- Food is trapped in gills’ sticky mucous, then cilia direct it to their mouth

Question 14

Respiration of marine mollusks

Answer 14

Use gills (usually located inside their mantle cavity)

Question 15

Gills of marine mollusks

Answer 15

Parts of the mantle that made of a system of filamentous projections like the fringes of a blanket
- Have a rich supply of blood to move oxygen to the blood and remove CO2 from the blood
- Move water into & through the mantle cavity in a continuous stream

Question 16

Respiration of Terrestrial mollusks

Answer 16

Breathe via diffusion through a specially adapted mantle cavity lined with many blood vessels
The mantle is highly folded to increase surface area, and is kept moist for efficient gas exchange

Question 17

Circulation (internal transport) of gastropods/bivalves

Answer 17

Open circulatory system: Blood travels through tissues and sinuses (open spaces) which lead to/from gills & heart for O2 and CO2 exchange
- An open system is efficient enough for sessile & sedentary (slow-moving) species

Question 18

Circulation of cephalopods

Answer 18

Closed circulatory system
- Too fast-moving (predators) to use the less efficient “open” system
- Blood travels within blood vessels, quickly delivers nutrients and oxygen

Question 19

Excretion of solid wastes

Answer 19

Leave via anus
Have a complete digestive system (one way street)

Question 20

Excretion of liquid wastes

Answer 20

Leave the blood via nephridia
After nephridia filter the blood, waste is passed out through the mantle cavity

Question 21

Nephridia

Answer 21

AN evolutionary adaptation that lets mollusks efficiently maintain homeostasis in their body fluids

Question 22

Response (nervous system) of bivalves

Answer 22

Simple
- Ganglia near their mouth, some nerve cords and simple sense organs
- Chemorecptors, touch receptors, statocysts, ocelli

Question 23

Response (nervous system) of cephalopods

Answer 23

Active, intelligent predators
- Well developed nervous system
- Brain and have great memory, many sense organs to sense shapes by sight and textures by touch
- Are trainable and often studied to observe how animals learn

Question 24

Response (nervous system) of Gastropods

Answer 24

All very different (no standard trend)

Question 25

Reproduction of mollusks

Answer 25

Separate sexes
External fertilization in most marine species- form free-swimming trochophore larvae

Question 26

Reproduction in cephalopods

Answer 26

Internal fertilization

Question 27

Reproduction in gastropods

Answer 27

Some gastropods are hermaphrodites- reproduce sexually in pairs

Question 28

Reproduction in bivalves

Answer 28

Certain bivalves (like oysters) can change their genders

Question 29

Reproduction cycles of clams

Answer 29

1. Female clam releases eggs into water, fertilized by sperm released by male clams
2. After fertilization, trochophore larvae change into veliger larvae. Both forms are free swimming
3. The veliger larvae shed their vellums- the ciliated “sails” that enable them to swim and settle on a surface
4. The final larval stage, the pediveligers, develop into adult clams

Question 30

Ecology of mollusks in the environment

Answer 30

“clean-up” surroundings (filter feeders, detritus feeders, etc.)
- Hosts to symbiotic algae and/or parasites
- Some are parasites
- Important source of food in their food web

Question 31

Ecology of mollusks in relation to human interests

Answer 31

Bivalves are used as environmental monitors because filter-feeding can concentrate dangerous pollutants/toxic microorganisms in their tissues
- Called biomagnification ex red tide
- Snails don’t get cancer
- Snails/slugs may damage crops/gardens
- Some bivalves may damage wood (drilling)

Question 32

Mollusk characteristics

Answer 32

• Have a coelom which allows for specialization of organ systems
• Bilaterally symmetrical
• visceral mass, food mantle
• One way digestive system with specialized organs and have feeding mouthparts
• Many have a highly developed cephalization with sensory organs
• Many have CaCO3 external shells
• Respire with gills to extract O2 and get rid of waste
• Many have radula (chitinous tongue for feeding)
• Sexual reproduction (separate sexes: dioecious)

Question 33

Movement of gastropods

Answer 33

Moves by sending waves of contractions along its muscular food
- a film of mucus lubricates the foot and helps propel the animal forward

Question 34

Movement of bivalves

Answer 34

most don’t move much unless threatened
- Uses its muscular foot to burrow into sediment or uses jet propulsion to flee

Question 35

Movement of cephalopods

Answer 35

Move by jet propulsion
To avoid predators, it draws in water through slits in the body wall then the water is pumped rapidly through the siphon, jet-propelling the cephalopod away from danger

Question 36

what development did mollusks go through

Answer 36

Prostome development

Question 37

Gills

Answer 37

parts of the mantle that consist of a system of filamentous projections like the fringes of a blanket
- Contain a rich supply of blood for the transport of oxygen to the blood and remove CO2
- Move water into and through the mantle cavity in a continuous stream
- Highly branched which increases surface area
- Sometimes used in filter feeding