Lecture 10 +11

Question 1

What type of organism is a mollusc?

Answer 1

A lophotrochozoan that is a Protostomia with triploblast development and a larval form called trochophore.

Question 2

What does “mollusca” mean, and how diverse is the phylum?

Answer 2

Mollusca” is Latin for “soft,” and it is an extremely diverse phylum with around 90,000 species across 8 classes.

Question 3

Where can molluscs be found, and what are their feeding habits?

Answer 3

Molluscs have a cosmopolitan distribution (marine, freshwater, and terrestrial) and can be carnivores, herbivores, filter feeders, or parasites.

Question 4

Why are molluscs important to humans?

Answer 4

They provide food (e.g., calamari, mussels), pearls, shells (used as currency like cowries), serve as bioindicators, pests, and have medical importance (e.g., shell strength, nerve cells).

Question 5

What are the main body regions of molluscs?

Answer 5

Molluscs have a Head-Foot region and a Visceral Mass.

Question 6

What is included in the Head-Foot region of molluscs?

Answer 6

he Head with sense organs (brain, eyespots, tentacles) and the Radula, a chitinous ribbon with teeth (absent in bivalves), and the Foot for locomotion, attachment, and mucus production.

Question 7

What is the function of the radula?

Answer 7

The radula is a chain-saw-like structure that carries teeth on a chitinous ribbon, used for feeding (absent in bivalves).

Question 8

What does the Foot region of a mollusc do?

Answer 8

The foot aids in locomotion, attachment, and can produce mucus for gliding.

Question 9

What is the Visceral Mass in molluscs?

Answer 9

It contains the internal organs (digestive, excretory, reproductive, and respiratory) and is covered by the Mantle.

Question 10

What is the mantle, and what does it do?

Answer 10

The mantle is the “skin” of the mollusc, often with muscles and chemoreceptors, and it secretes the shell.

Question 11

Describe the mantle cavity in molluscs.

Answer 11

The mantle cavity is open to the environment, allowing water to flow around organs for excretion, respiration, and sometimes jet propulsion.

Question 12

What are the three layers of the mollusc shell?

Answer 12

Periostracum: outer organic layer, resistant and thin with dark coloration.
Prismatic layer: middle layer, thick with calcium carbonate.
Nacre: inner layer, “mother of pearl,” continuously thickens.

Question 13

How are pearls formed in molluscs?

Answer 13

When dirt enters between the shell and mantle, nacre is secreted around it, forming a pearl over time.

Question 14

What are some basic internal characteristics of molluscs?

Answer 14

Bilaterally symmetric coelomates with reduced coeloms.
Most have an open circulatory system and a complex digestive system.

Question 15

Describe the respiratory structures in molluscs.

Answer 15

Molluscs have a mantle cavity for respiration, which may include gills, lungs, or allow diffusion, open to the environment.

Question 16

What are the different nervous system types in molluscs?

Answer 16

They range from simple (or non-existent) to complex brains and centralized nervous systems.

Question 17

Describe the reproductive system in molluscs.

Answer 17

Mostly not asexual.
Can be dioecious (separate sexes) or monoecious (hermaphroditic).
Have trochophore larvae and commonly veliger larvae in aquatic forms

Question 18

What are the two main clades in the old phylogeny of molluscs?

Answer 18

Aculifera and Conchifera.

Question 19

What classes are included in the Aculifera clade?

Answer 19

Class Caudofoveata, Class Solenogastres, and Class Polyplacophora.

Question 20

what are the classes in the Aplacophorans

Answer 20

Class Caudofoveata, Class Solenogastres

Question 21

What are some characteristics of Class Caudofoveata and Solenogastres (spicule worms)

Answer 21

Wormlike, shell-less, with calcareous scales/spicules, reduced head, no foot, and are marine burrowers consuming detritus/microorganisms.

Question 22

What defines Class Polyplacophora, also known as chitons?

Answer 22

They have 8 movable plates, a mantle girdle around the body, a central foot, multiple gills along the mantle cavity, and are intertidal grazers on hard surfaces.

Question 23

What is unique about Class Monoplacophora?

Answer 23

Known as “one plate” molluscs with a single cap-like shell, serial repetition of soft parts, and are deep-sea grazers on hard surfaces.

Question 24

Which class is the most diverse within the molluscs, and what organisms does it include?

Answer 24

Class Gastropoda, with around 70,000 species including snails, periwinkles, limpets, sea slugs, and slugs.

Question 25

What are the main functional groups of gastropods, and what do they mean?

Answer 25

Prosobranchia: Gills in front of the heart, mainly marine snails.
Opisthobranchia: Gills behind the heart, mostly shell-less forms like nudibranchs.
Pulmonata: Air-breathing, land, and freshwater snails and slugs with modified mantle cavities as lungs.

Question 26

Explain torsion and coiling in gastropods.

Answer 26

Torsion: 180° rotation of soft body parts, positioning the anus near the mouth.
Coiling: Spiral shell development for protection and weight distribution.

Question 27

Describe gastropod feeding .

Answer 27

Feeding: Varied radula adaptations for scraping, drilling, or piercing.

Question 28

Describe gastropod reproductive adaptations.

Answer 28

Simultaneous hermaphrodites, “love darts,” and eversible gonopores for simultaneous sperm transfer.

Question 29

What defines Class Bivalvia, and what organisms belong to it?

Answer 29

Bivalvia includes clams, mussels, oysters, scallops, etc., characterized by two-valve shells, no head or radula, and a laterally compressed body.

Question 30

How do bivalves feed and move?

Answer 30

They use a large pair of ctenidia for filter feeding and respiration, burrow with their foot, swim with adductor muscles, or attach via byssal threads.

Question 31

What are the main features of Class Scaphopoda?

Answer 31

Known as tusk or tooth shells, they have tubular shells open at both ends, rely on diffusion, and use a tentacular foot for burrowing and food capture.

Question 32

What defines Class Cephalopoda, and which organisms are included?

Answer 32

Cephalopoda, meaning “head-foot,” includes squid, octopus, nautilus, and cuttlefish, known for their predatory nature, arms, tentacles, siphons, and closed circulatory systems.

Question 33

How do cephalopods use their siphon for movement?

Answer 33

Cephalopods use jet propulsion by expelling water through the siphon, directing movement, aided by arms and tentacles with suckers.

Question 34

What are cephalopods’ adaptations for camouflage and defense?

Answer 34

They use chromatophores, ink sacs filled with melanin (and sometimes mucus), and have advanced eyes and nervous systems for complex behaviors.

Question 35

Describe cephalopod reproduction and lifespan

Answer 35

Cephalopods are dioecious with direct development, and most species die after a single reproductive event (semelparous)