K.2 Phylum Mollusca

What are the three main characteristics of molluscs?

Mantle (secretes shell), Muscular foot (movement), Soft body (visceral mass).

What is the mantle?

A specialized tissue that secretes calcium carbonate to form the shell.

What is the visceral mass?

The soft internal organs of the mollusc.

What is the function of the foot in molluscs?

Locomotion.

What type of skeleton do molluscs have?

Exoskeleton (external shell), not an endoskeleton.

What is the main trade-off of having an exoskeleton?

Protection vs mobility.

What is a bivalve?

A mollusc with two shells hinged together.

What is the lifestyle of most bivalves?

Sessile or slow-moving filter feeders.

How do bivalves feed?

By filtering water for food particles.

What are siphons used for?

Bringing water in (incurrent) and pushing water out (excurrent).

What happens in the bivalve siphon system?

Water brings in oxygen and food, and removes waste.

What are labial palps?

Structures that help direct food into the digestive tract.

Why can bivalves survive in intertidal zones?

They can close their shells to retain water.

What is nacre?

A smooth shell lining that can form pearls.

Do bivalves have a closed or open circulatory system?

A partially open circulatory system.

What is the function of the two-chambered heart in bivalves?

Pumps blood into tissues via sinuses.

What are sinuses in bivalves?

Open spaces where blood bathes tissues.

How do bivalves move using their foot?

By extending it into sand, swelling it with blood, and pulling themselves forward.

How do bivalves reproduce?

By broadcasting gametes into water.

Are bivalves male, female, or both?

Separate sexes (dioecious).

What larval stage do bivalves produce?

Trochophore larva.

Why is the trochophore stage important?

It suggests evolutionary links with annelids.

What animals are gastropods?

Snails and slugs.

What does “gastropod” mean?

“Stomach-foot.”

What is the main difference between snails and slugs?

Snails have shells; slugs do not.

What is the function of the snail mantle?

Produces shell material as the snail grows.

How do slugs protect themselves?

Camouflage and foul-tasting secretions (“ink”).

What is the gastropod foot used for?

Crawling using muscular movement and mucus.

What do gastropods eat?

Mostly plants (herbivores).

What is a radula?

A tongue-like structure with tiny teeth used for scraping food.

Do gastropods show cephalization?

Yes, they have a distinct head region.

What sensory structures do gastropods have?

Light-sensitive eyes on retractable antennae.

Is the gastropod circulatory system open or closed?

Open circulatory system.

What does “cephalopod” mean?

“Head-foot.”

What is the main feature of cephalopods?

Highly developed head and tentacles with suckers.

What type of circulatory system do cephalopods have?

Closed circulatory system.

Why do cephalopods need a closed circulatory system?

To support fast movement and high energy demand.

How do squids and octopuses differ in movement?

Squids swim rapidly; octopuses crawl more and swim occasionally.

What defense mechanism do cephalopods use?

Ink release.

Why are cephalopod eyes advanced?

They form clear images using a lens and retina.

What is the structure of a cephalopod eye?

Fluid-filled chamber with a lens focusing light on a retina.

Do cephalopods have eyelids?

No, but they have iris-like structures controlling light entry.