Phylum Mollusca Notes

Phylum Mollusca Notes

​What Is a Mollusk?

• ​Mollusk or mollusc means soft body

• Mollusks are soft-bodied animals that usually have an internal or external shell.

​

​What Is a Mollusk?

• Mollusks include snails, slugs, clams, squids, and octopi.

• Many Mollusks share similar developmental stages.

​

Multiple Choice

What is the Latin meaning of the word Mollusca?

• Soft-bodied

• Stomach foot

• Head-footed

• Two-shelled

Multiple Choice

In a mollusk the shell can be

• internal and external

• only internal

• only external

• internal, external or absent

​Characteristics of Mollusks

​1.Body has two parts:  head-foot and visceral mass

2.Mantle that secrets a calcareous shell that covers the visceral mass

3.Mantle cavity functions in excretion, gas exchange, elimination of digestive wastes, and release of reproductive products

​Characteristics of Mollusks Continued

4.Bilateral symmetry

5.All Molluscs have a soft body, and most Molluscs have an internal or external shell.

​Characteristics of Mollusks Continued

6. Protostome characteristics

• ​​spiral and determinate cleavage

• ​mouth forms from blastopore

7. Eucoelom reduced to cavities surrounding the heart, nephridia, and gonads

​Characteristics of Mollusks Continued

8. Open circulatory system in all but one class (Cephalopoda)

9. Radula usually present and used in scraping food

Multiple Choice

The protective shell of a mollusk...

• is secreted by the mantle.
• Grows from the end of the mollusk foot. 
• Is constantly replaced by bigger shells as the mollusk grows. 
• forms when the mollusk reaches adulthood. 

Multiple Choice

What type of symmetry do MOST mollusks have?

• Bilateral
• Radial
• Circular
• Asymmetrical

Multiple Choice

True or false : All mollusks except those in the class Cephalopoda have an open circulatory system.

• true

• false

​What Is a Mollusk?

• ​Many aquatic Mollusks have a free-swimming larval stage called a trochophore.

  The trochophore larva is also characteristic of annelids, indicating that these two groups may be closely related.

Multiple Choice

The mollusk larval stage of development is called the

• coelomate
• trochopore
• radula
• cephalopod

Multiple Select

How are Mollusks similar to Annelids? (select all that apply)

• Bilaterally symmetrical

• True Coelomate

• Segmented

• Trochophore Larva

​Form and Function in Mollusks

• ​Mollusks have eucoelom (true coeloms) surrounded by mesoderm tissue

  They have complex, interrelated organ systems that function together to maintain the body as a whole

  • they are more complex than flatworms and roundworms

Multiple Choice

Which of the following is the correct description of the body cavity of Mollusks?

• They are protostome acoelomates

• They are protostome coelomates

• They are deuterostome coelomates

• They are protostome pseudocoelomates

​Form and Function in Mollusks

The body plan of most Mollusks has four parts:

1. Head - foot – contains mouth, nervous and sensory structures, foot used for attachment and locomotion

2. Mantle – attached to visceral mass and overlies the visceral mass

3. Shell – used for protection

4. Visceral mass – contains organs for digestion, circulation, reproduction, and excretion

Multiple Choice

Which of the following would contain the vital organs of a mollusk?

• Visceral mass

• Mantle

• Head

• Foot

​The muscular foot takes many forms

• flat structures for crawling

• spade-shaped structures for burrowing

• tentacles for capturing prey

​

Feeding 

• Mollusks can be herbivores, carnivores, filter feeders, detritivores, or parasites.

  Snails and slugs feed using a flexible, tongue-shaped structure known as a radula.

• Hundreds of tiny teeth are attached to the radula.

  The radula is used to scrape algae off rocks or to eat the soft tissues of plants.

• ​Clams, oysters, and scallops use gills.

  Food is carried by water, which enters the incurrent siphon.

• A siphon is a tube-like structure through which water enters and leaves the body.

  The water flows over the gills while the food and oxygen are pulled out of it. and leaves by the excurrent siphon.

Multiple Choice

Which part of the Mollusk body is specialized for burrowing, feeding, and movement?

• trochophores
• visceral mass
• mantle
• foot

Multiple Select

The muscular foot of a mollusks can take many forms, each with different function. Select all the forms the foot can take with their correct function.

• tentacles for grabbing and capturing prey

• ridged for gathering particles

• broad and flat for crawling

• spade-shaped for digging and burrowing

• round and thick for smashing

Multiple Choice

Filter-feeding bivalves can be used to monitor the environmental health of a habitat because the ____ . 

• a. bivalves reproduce rapidly in polluted water
• b. bivalves concentrate pollutants and microorganisms in their tissues.
• c. bivalves live near deep-sea vents.
• d. Bivalves only live above ground. 

Multiple Choice

How do Bivalves eat?

• Filter feeders

• Radula

• Tentacles

• Beak

Multiple Choice

Mollusk's tongue-like strip covered with teeth that point backward is called the ____

• trochopore
• radula
• gills
• visceral mass

​Respiration

​•Aquatic Mollusks breathe using gills inside their mantle cavity.

•As water passes through the mantle cavity, oxygen in the water moves into blood flowing through the gills.

​Respiration

•At the same time, carbon dioxide moves in the opposite direction.

•Land snails and slugs respire (breath) using a mantle cavity that has a large surface area lined with blood vessels.

​Circulation 

• ​Some Mollusks have open circulatory systems (slow moving mollusks);

• other Mollusks have closed circulatory systems (fast moving mollusks).

​Circulation 

• A closed circulatory system can transport blood through an animal’s body more quickly than an open circulatory system.

• ​In an open circulatory system, blood is pumped through incomplete vessels by a simple heart.

Multiple Choice

Which class of Mollusks have a closed circulatory system?

• Gastropods
• Bivalves
• Cephalopods
• All of the classes

Multiple Choice

Which of the following is the correct description of respiration in Mollusks?

• They use diffusion through their moist skin and gills in marine environments
• They use primitive lungs in marine environments and gills on land.
• They use nephridia to exchange oxygen and carbon dioxide
• They use gills in marine environments and primitive lungs on land.

​Response 

• Two-shelled Mollusks have a simple nervous system.

  • 3 sets of ganglia

  • 2 sets of nerve cords.

​

• The complexity of the nervous system and the ability to respond to environmental conditions varies among Mollusks.

​

​Response 

• Well-developed brains in these animals allows them to remember things for long periods.

​

• Octopi and their relatives have the most highly developed nervous system of all invertebrates.

​

​Movement 

• ​Snails secrete mucus along the base of the foot, and then move over surfaces using a rippling motion of the foot.

• Octopus draws water into the mantle cavity and then forces the water out through a siphon.

  • Water leaving the body propels the octopus in the opposite direction.

​Reproduction 

• ​Some Mollusks reproduce sexually by external fertilization.

  In other Mollusks, fertilization takes place inside the body of the female.

  Some Mollusks are hermaphrodites and usually fertilize eggs from another individual.

Multiple Choice

Mollusks are the first phylum that have all of the following well-developed systems except?

• Digestive

• Excretory

• Circulatory

• Nervous

​Groups of Mollusks

• ​Class: Gastropoda (gastro = stomach, poda = foot)

  Gastropods are shell-less or single-shelled Mollusks that move by using a muscular foot located on the ventral side. 

​Groups of Mollusks

• Many gastropods have a single shell that protects their bodies.

  • When threatened, they can pull completely into their shells

• Gastropods include: 

  • pond snails, land slugs, sea butterflies, sea hares

• ​ Torsion

  • only occurs in Gastropods

  • ​twisting of the body 180 ^O during development

Multiple Choice

Gastropods can twists the body round so that the anus, reproductive organs, mantle cavity and gills all point forward. What it is called?

• Fusion

• Torsion

• Excretion

• Respiration

Multiple Choice

What is the meaning of Gastropod?

• Soft-bodied
• Stomach foot
• Head-footed
• Two-shelled

Multiple Choice

Land snails tend to be hermaphrodites, but many aquatic snails are _____________.

• Monoecious
• Asexual
• Dioecious 
• Self-fertilizing

​​Groups of Mollusks

• ​Class: Bivalvia (bi = two, valve = shell)

  Bivalves have two shells that are held together by one or two powerful muscles called adductor muscles.

​​Groups of Mollusks

• ​Common bivalves include:

  • Clams, oysters, mussels, scallops

Multiple Choice

How are pearls formed?

• All bivalves form them as part of their lives!

• Irritant gets between shell & mantle and is covered with nacre

• Pearls are result of retained digestive wastes

• Extension of the shell formed for extra protection

Multiple Choice

What structure is used to close the shell of bivalves?

• adductor muscles
• restrictor muscles
• umbo
• hinge ligament

Multiple Choice

What does the prefix bi- mean?

• two
• leaf
• shell
• foot

Multiple Choice

The oldest and thickest part of the bivalve shell is called the

• periostracum
• operculum
• umbo
• valve

​​Groups of Mollusks

• ​Class: Cephalopoda (cephalo = head, poda = foot)

  Cephalopods are typically soft-bodied Mollusks in which the head is attached to a single foot.

  • foot is divided into tentacles or arms.

​​Groups of Mollusks

• Cephalopods have eight or more tentacles equipped with sucking disks that grab and hold prey.

• Most modern cephalopods have only small internal shells or no shells at all.

​​Groups of Mollusks

• The only present-day cephalopods with external shells are nautiluses.

​​Groups of Mollusks

• Specialized cells called Chromatophores that allow them to camouflage themselves in their environment are present in the mantle of cephalopods.

​​Groups of Mollusks

• Cephalopods have complex sense organs that help them detect and respond to external stimuli.

• Cephalopods distinguish shapes by sight using complex eyes and texture by touch.

​​Groups of Mollusks

• Only Class with direct development

• Cephalopods include:

  • Squid, Octopi, Cuttlefish, and Nautilus

Multiple Choice

The cells in skin of cephalopods that allow them to change colors are called

• pigmentocytes
• chromatophores
• dermatophores
• branchiocytes

Multiple Choice

What does Cephalopod mean?

• means "2-shells"
• means "head-foot"
• means "stomach-foot"
• means "soft bodied"

Multiple Choice

Among mollusks, which is a special characteristic of cephalopods?

• an open circulatory system.
• a two way digestive system.
• the only mollusk class with gills.
• a closed circulatory system.

Multiple Choice

Which of these cephalopods has an external shell?

• cuttlefish
• squid
• octopus
• nautilus

Multiple Choice

What are the major groups of Mollusks?

• Cnidarians, Gastropods, Porifera
• Gastropods, Bivalves, Cephalopods
• Porifera, Cephalopods, Cnidarians

Multiple Select

Name the THREE groups of Mollusks.

• Gastropods

• Arthropods

• Cephalpods

• Bivalves

Multiple Choice

The protective membrane that surrounds the visceral mass on all mollusks is called...

• Radula
• Mantle
• Nephridia
• Visceral Shield 

Multiple Choice

Which of these is NOT one of the three main body parts of a mollusk? 

• Head
• Valve
• Foot
• Visceral Mass