Class Gastropoda Overview

Study Notes

Class Gastropoda

Largest and most diverse mollusk class with around 40,000 species, including 15,000 documented in fossils.
Exhibits bilateral symmetry; many shelled forms experience torsion during the larval veliger stage, resulting in asymmetry where the digestive tract points toward the head.

Unique Anatomical Features

Anus location on the head leads to accumulation of waste, influencing their growth and coiling patterns.
Coiling occurs in two planes: vertically and laterally (to the left or right).

Subclassifications

Pulmonates: Terrestrial snails and slugs with lung-like structures in the mantle cavity. Some evolved back to aquatic environments, requiring breathing from the surface.
Opisthobranchs: Includes sea slugs, nudibranchs, sea hares, exhibiting sensory tentacles and monoecious reproduction. They can be grazers or predators, particularly on cnidarians.
Prosobranchs: Classic marine snails characterized by spiral shells and two sets of gills in the mantle cavity, along with a single set of tentacles.

Class Cephalopoda

Noted for high intelligence levels, primarily pelagic lifestyle in upper water columns.
Foot evolved into a head region with specialized tentacles, eyes, and a complex brain.
All members are dioecious and engage in elaborate mating rituals, showcasing advanced visual signals and some, like squids, are bioluminescent.

Eye Evolution

Both arthropods and molluscs have developed compound eyes for enhanced vision.
Cephalopods draw water into their mantle cavity for respiration and utilize jet propulsion for efficient movement, as seen in nautiloids from the Mesozoic era.

Ammonites and Chromatophores

Ammonites are ancient nautiloids with distinctive spiral shells, utilizing ink for predator evasion.
Chromatophores are special cells in cephalopods containing expandable pigment sacs, enabling color change. Most cephalopods possess three pigments: brown, yellow, and black.

Description

Explore the fascinating class of Gastropoda, the largest and most diverse group of mollusks. This quiz covers their unique anatomical features, subclassifications including Pulmonates, Opisthobranchs, and Prosobranchs, and their fascinating life cycle processes. Test your understanding of the diversity and characteristics that define this intriguing class.