Phylum Mollusca Part 2: Class Gastropoda (Slugs and Snails)

Introduction to Gastropods

This section introduces the class Gastropoda, highlighting its diversity and widespread distribution in various environments.

Characteristics of Gastropods

• Gastropods are diverse, ranging from microscopic forms to large marine animals like the giant horse conch and sea hares.

• They inhabit a wide range of environments including gardens, woodlands, deserts, rivers, lakes, estuaries, polar regions, mudflats, and hydrothermal vents.

• Classification of gastropods has been debated with traditional classification recognizing three major subclasses: Prosobranchia, Opisthobranchs, and Pulmonates.

• Alternative classifications include Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda, and Heterobranchia.

Shell Structure and Function

• Gastropod shells are univalve and ornate; they are secreted by live mollusks.

• Shells start at the apex with successively larger whorls spiraling around the columella. Chirality or "handedness" is a common feature.

• Torsion is a key characteristic involving a 180-degree twisting of the visceral mass during development.

Unique Adaptations

• Torsion leads to unique anatomical features such as the rotation of the shell and positioning of anus above the head for protection.

• Asymmetry in shell structure influences body alignment for better weight distribution and avoidance of fouling.

Gastropod Feeding Strategies

This section explores the diverse feeding strategies of gastropods, highlighting their varied approaches to obtaining nutrition.

Gastropod Feeding Strategies

• Gastropods like abalones and garden slugs use their radula to break off food pieces.

• True whelks are scavengers, while oyster borers drill holes into oysters using modified radula and chemicals.

• Carnivorous species such as cone snails inject conotoxins for prey consumption.

• Some gastropods, like sea butterflies, entangle plankton in mucous webs for feeding.

• The "leaf sheep" sea slug practices kleptoplasty by retaining chloroplasts from algae for photosynthesis.

Unique Adaptations in Gastropods

This section delves into the unique adaptations and symbiotic relationships of certain gastropod species.

Unique Adaptations

• Sacoglassans practice kleptoplasty by retaining chloroplasts from algae they consume.

• Scaly-foot gastropods at hydrothermal vents rely on chemoautotrophy from endosymbiotic bacteria for nutrition.

Gastropod Locomotion and Respiration

The locomotion mechanisms and respiratory systems of gastropods are discussed in this segment.

Locomotion and Respiration

• Gastropods use a foot for locomotion, aided by muscular waves and pedal mucus adhesion.

• Sea angels and sea butterflies propel themselves through water using modified foot "wings."

• Most gastropods respire through ctenidia or specialized gills, while land-dwelling species utilize lung-like structures in their mantle cavity.

Reproduction and Courtship in Gastropods

Reproductive strategies and courtship rituals among various gastropod species are explored here.

Reproduction and Courtship

• Gastropods exhibit diverse reproductive strategies including internal fertilization, dioecious, monoecious, and protandric characteristics.

• Prolonged courtship ceremonies involving love darts promote sperm preservation in some gastropod species.