Prosobranchs and Pulmonates Anatomy

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Questions and Answers

What is the primary function of the radula in molluscs?

To rasp and scrape for feeding (correct)

To digest food

To sense light

To aid in locomotion

What is the outermost layer of a mollusc shell?

Periostracum (correct)

Prismatic layer

Mantle layer

Nacreous layer

What is the purpose of the mantle cavity in molluscs?

To store food

To contain the respiratory organs (correct)

To house the radula

To aid in digestion

What is the characteristic of the circulatory system in most cephalopods?

Closed circulatory system Signup and view all the answers

What is the name of the free-swimming, ciliated larval stage in molluscs?

Trochophore Signup and view all the answers

What is the function of the nacreous layer in mollusc shells?

To form pearls Signup and view all the answers

What adaptation do derived prosobranchs have to improve respiratory efficiency?

Loss of one gill and half of the remaining gill Signup and view all the answers

What is the function of the pneumostome in pulmonates?

To open to the outside for gas exchange Signup and view all the answers

What is the direction of coiling in shells determined by?

Genetic control Signup and view all the answers

What type of reproductive system is characteristic of most freshwater snails?

Ovoviviparity Signup and view all the answers

What is the primary function of the radula in most gastropods?

Scraping algae off hard surfaces Signup and view all the answers

What is the main difference between planospiral and conispiral shells?

The position of each whorl relative to the others Signup and view all the answers

What is the term for the rotation of the mantle cavity to an anterior position?

Torsion Signup and view all the answers

What is the purpose of the operculum in many snails?

To close off the shell Signup and view all the answers

What is the sense organ found at the base of the incurrent siphon in some gastropods?

Oosphradium Signup and view all the answers

What is the conclusion about the classification of Prosobranchia based on recent evidence?

It is a paraphyletic group Signup and view all the answers

What is the function of ctenidia in many gastropods?

Respiration in the mantle cavity Signup and view all the answers

What is unique about the radula of snails in the genus Conus?

It is modified into a drill for boring through shells Signup and view all the answers

What is the function of the funnel in cephalopods?

To control the direction of swimming Signup and view all the answers

How do cephalopods communicate?

Through visual signals and body language Signup and view all the answers

What is the function of the ink sac in cephalopods?

To defend against predators Signup and view all the answers

What is unique about the circulatory system of cephalopods?

It is a closed circulatory system Signup and view all the answers

What is special about the brain of cephalopods?

It is the largest of any invertebrate Signup and view all the answers

How do cephalopods reproduce?

Sexes are separate and juveniles hatch from eggs Signup and view all the answers

What is the main function of the muscular foot in bivalves?

To extend and move the organism around Signup and view all the answers

What is the purpose of the tiny teeth on the valves of shipworms?

To burrow through wood and create tunnels Signup and view all the answers

What is the main reason why native freshwater clams in the U.S. are jeopardized?

Due to their sensitivity to water quality changes Signup and view all the answers

What is the purpose of the statocysts in the foot of bivalves?

To maintain balance and orientation Signup and view all the answers

What is the function of the osphradia in the mantle cavity of bivalves?

To detect chemical changes in the environment Signup and view all the answers

What is the main purpose of the scallops' row of small blue eyes along the mantle edge?

To detect predators and react to threats Signup and view all the answers

Study Notes

Head-Foot Region

Most molluscs possess a well-developed head with sensory structures such as photosensory receptors.
Cephalopods have complex eyes, while other molluscs mostly have simple light detectors.
The radula, a unique rasping feeding structure, is present in most molluscs except bivalves, featuring a ribbon-like membrane with rows of tiny teeth.
The foot of a mollusc can be adapted for locomotion, attachment, or both; pelagic species may have wing-like parapodia.

Shell Structure

When present, the calcareous shell is secreted and lined by the mantle, consisting of three layers:
- Periostracum: outer organic layer providing protection against boring organisms.
- Prismatic layer: composed of densely packed calcium carbonate prisms.
- Nacreous layer: iridescent lining continuously secreted by the mantle; can envelope foreign objects to form pearls.

Mantle Cavity

The mantle cavity is the space between the mantle and visceral mass, typically housing respiratory organs (gills or lungs).

Internal Structure and Function

Most molluscs have an open circulatory system, while cephalopods boast a closed circulatory system.
Internal structures include a heart, blood vessels, and blood sinuses, enabling efficient circulation.

Mollusc Life Cycle

Majority of molluscs are dioecious, with some being hermaphroditic.
They undergo a trochophore larval stage which is free-swimming and ciliated, similar to annelid larvae.

Class Bivalvia

Shipworms, destructive to wharves and ships, feature valves with tiny teeth used for burrowing into wood.
They feed on wood particles aided by symbiotic bacteria producing cellulase and fixing nitrogen.
U.S. native freshwater clams face extinction threats, with over 300 species once present and several now endangered.
Zebra mussels are an invasive species problematic for the Great Lakes region.

Bivalve Locomotion

Bivalves move using a muscular foot that extends between their shells, while scallops and file shells can swim by clapping their shells for jet propulsion.

Bivalve Anatomy

Scallops possess a row of small blue eyes along the mantle edge, capable of forming images.
Anatomy includes a pair of U-shaped kidneys and a nervous system with three pairs of ganglia; sense organs are poorly developed.
Statocysts (balance organs) are present in the foot, while the osphradia in the mantle cavity serve as chemoreceptors.

Class Cephalopoda

Cuttlefish possess a small curved shell, while squid have a reduced shell known as a pen.
Cephalopods utilize jet propulsion by expelling water from the mantle cavity through a funnel, allowing directional control.
They feature a closed circulatory system and advanced nervous and sensory systems, including complex eyes.

Cephalopod Communication

Communication involves visual signals, body and arm movements, and chromatophores that enable color changes via pigment granule manipulation.
Most cephalopods have an ink sac secreting sepia, an ink used for defense against predators, facilitating escape.

Cephalopod Reproduction

Most species have separate sexes, and juveniles hatch directly from eggs without free-swimming larvae; includes adaptations like the loss of one gill for respiratory efficiency.

Pulmonate Internal Structure

Aquatic pulmonates have a highly vascular mantle area functioning as a lung; they possess a pneumostome for gas exchange.
Internal features include a single nephridium and developed circulatory/nervous systems, with sensory organs such as eyes and chemoreceptors.

Major Groups of Gastropods

Traditional classifications of Gastropoda include three subclasses: Prosobranchia, Opisthobranchia, and Pulmonata, with ongoing debates about their paraphyly.
Prosobranchia encompasses most marine snails and some freshwater/teterristrial gastropods, with shell features controlled genetically.

Gastropod Morphology

Gastropods exhibit bilateral symmetry, transformed into asymmetry via torsion, which occurs during larval development.
Coiling differs from torsion, resulting in specific shell shapes that offer balance and distribution advantages.

Gastropod Feeding Habits

Most gastropods are herbivores, utilizing the radula to scrape algae; some are scavengers or carnivores employing specialized radulas for capturing prey.
Notable genera include Conus, which paralyze prey with toxic secretions, with some toxins potentially harmful to humans.
Flamingo tongue snails are bright-colored, feeding on gorgonians while enveloping their shells with their mantle.

Gastropod Respiration

Respiration occurs through ctenidia located in the mantle cavity, facilitating vital gas exchange.

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Description

Learn about the internal form and function of prosobranchs and pulmonates, including their respiratory systems, gills, and lungs. Understand the differences between these two types of mollusks.