Phylum Molluscs Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which characteristic is NOT found in molluscs?

Real coelom

Soft body

Segmented body (correct)

Mantle cavity

Which class of molluscs is known for having a shell made of calcium carbonate?

Gastropoda (correct)

Bivalvia (correct)

Amphineura

Cephalopoda (correct)

What is the primary feeding mechanism of bivalves?

Radula

Siphons

Tentacles

Filter feeding (correct)

Which part of the mollusc's body may be modified to form tentacles?

Muscular foot Signup and view all the answers

What type of development do molluscs typically undergo?

Indirect development with a larval stage Signup and view all the answers

Which of the following is true about the respiratory system of molluscs?

It has gills or pulmonary sacs Signup and view all the answers

What characteristic is unique to organisms in the Subphylum Amphineura?

Lack of eyes and tentacles Signup and view all the answers

What term describes the reproductive strategy of most bivalves?

Gonochoristic with indirect development Signup and view all the answers

What is a defining feature of the Class Gastropoda that distinguishes it from other molluscs?

Asymmetrical body structure Signup and view all the answers

In what way is the reproductive strategy of gastropods differentiated from that of bivalves?

Gastropods are exclusively hermaphroditic. Signup and view all the answers

Which physiological adaptation allows cephalopods to achieve rapid swimming capabilities?

Siphons for water expulsion Signup and view all the answers

What structural feature is unique to the subphylum Conchifera?

Shell made of calcium carbonate Signup and view all the answers

How does the process of torsion in gastropods affect their body structure?

It results in the twisting of internal organs. Signup and view all the answers

What is a characteristic of Bivalvia that is crucial for their feeding mechanism?

Adaptation of siphons for water filtration. Signup and view all the answers

Which adaptation is NOT typically found in members of the Class Cephalopoda?

Development of a spiral coiled shell Signup and view all the answers

What distinguishes the Class Bivalvia from other molluscan classes regarding body symmetry?

They exhibit bilateral symmetry. Signup and view all the answers

Which mollusc class is known for lacking a head and having a distinct feeding mechanism?

Bivalvia Signup and view all the answers

Which feature makes the chambered nautilus unique among cephalopods?

External shell composed of chambers Signup and view all the answers

What defines the circulatory system of most molluscs?

It consists of an open system with hemolymph and a heart with one ventricle and multiple atria. Signup and view all the answers

What role does the radula play in the digestive system of molluscs?

It acts as a rasping organ to aid in feeding. Signup and view all the answers

What is the typical structure of the nervous system in molluscs?

It has a ladder-like arrangement of ganglia with pairs controlling different body functions. Signup and view all the answers

What distinguishes the mantle of molluscs?

It secretes a calcium carbonate shell and forms a cavity. Signup and view all the answers

Which of the following best describes the reproductive system of terrestrial molluscs?

They display gonochorism with direct development. Signup and view all the answers

Which feature of molluscs is most likely to vary between aquatic and terrestrial species?

Type of respiratory structure. Signup and view all the answers

What is the significance of the mantle cavity in molluscs?

It accommodates gills or pulmonary sacs for respiration. Signup and view all the answers

How does the muscular foot of molluscs typically adapt in cephalopods?

It evolves into tentacles for capturing prey. Signup and view all the answers

What type of development do marine species of molluscs typically undergo?

They undergo indirect development with distinct larval stages. Signup and view all the answers

What substance contributes to the color and strength of the shells produced by molluscs?

Calcium carbonate Signup and view all the answers

Study Notes

Phylum Molluscs

Molluscs are a diverse group of invertebrates.
They are characterized by a soft body often with a hard shell made of calcium carbonate.
Key characteristics include a true body cavity (coelom), a soft non-segmented body and parts of the body include a head, muscular foot, visceral mass and mantle cavity situated between the mantle and body.
Body systems include an epidermis with mucus glands, smooth muscles on the foot (including modified tentacles), a complete digestive system (mouth-anus, opening to mantle cavity); a radula (a rough grater-like tongue), and a hepatopancreas.
The respiratory system (RS) comprises gills or pulmonary sacs.
The circulatory system (CS) is open, with haemolymph, a heart with one ventricle and atrium.
The excretory system (ES) includes metanephridia.
The nervous system (NS) is gangliated and specialized, with eyes and haptic organs.
Reproduction in molluscs involves gonochorism (separate sexes) or hermaphroditism (both sexes in one organism). Fertilisation is typically internal, with direct or indirect development (through larvae).

Subphylum Amphineura

Amphineura are primitive marine organisms.
They do not have a shell.
They have no eyes or tentacles.

Subphylum Conchifera

Conchifera have shells made of calcium carbonate (CaCO3).
Conchifera are divided into three main classes:
- Gastropoda
- Bivalvia
- Cephalopoda

Class Gastropoda

Gastropods have asymmetrical bodies.
Their shell is spiral-shaped.
They have a head with eyes and tentacles.
They have a modified muscular foot.
Gonochorists or hermaphrodites, often proterandrous (first male, later female).
Body torsion is present.
Examples include Carpathian blue slug, white-lipped snail, edible snail, garden slug.
Other examples are Planorbarius cornes, Viviparus viviparus and Lymnea stagnalis.

Class Bivalvia

Bivalves are exclusively aquatic.
Their respiratory system (RS) includes gills.
Their shell is composed of two valves joined by a ligament and muscles.
They lack heads, radulae and are filter feeders.
Reproduction is gonochoristic and development is indirect.
Examples include the swan mussel (Anodonta cygnaea) and painter's mussel (Unio pictorum).

Class Cephalopoda

Cephalopods are exclusively marine.
They lack or have reduced shells (e.g., cuttlebone).
They are carnivorous.
They use jet propulsion for locomotion.
Their muscular foot has been modified into tentacles equipped with suckers.
They have closed circulatory systems (CS) and gills.
Examples include chambered nautilus (Nautilus pompilius), common cuttlefish (Sepia officinalis), and common octopus (Octopus vulgaris).

Mollusc Characteristics

Well-developed nervous system
Ink sac (present in some cephalopods)
Chambered eyes (in some species)
Colour change (in some species)
Luminescence (in some species)
Gonochoristic or hectocotylus (modified arm for sperm transfer).
Direct or indirect development (through larvae).
Intelligent (learning and memory) in some species

Importance of Molluscs

Intermediate hosts for various parasites and pathogens (disease vectors).
Food source.
Pearls are produced by some bivalves.
Production of shells and pearls.
Some are pests.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the fascinating world of molluscs, a diverse group of invertebrates defined by their soft bodies and often protective shells. This quiz covers key characteristics, body systems, and reproductive methods of molluscs, providing insights into their complex biology. Test your knowledge on their anatomy, physiology, and ecological significance.