Class Bivalvia Characteristics Flashcards

Class Bivalvia Characteristics

• Bivalves possess a shell made of two hinged valves that close using adductor muscles.
• They have a rudimentary head and lack a radula.
• The foot is laterally compressed, enabling penetration into substrates.
• Notable features include a pair of large bipectinate gills and a pair of nephridia.
• The posterior edges of the mantle can form siphons.

Feeding Mechanism

• Food capture begins when particles enter the incurrent siphon and travel to the gills.
• Gills use cilia to collect particles, guiding them to the mouth area, then to the stomach, intestines, and out via the excurrent siphon.
• Bivalves are primarily filter feeders, but some species exhibit alternative feeding strategies, including boring, detritivory, carnivory, and symbiotic relationships with bacteria or zooxanthellae.

Reproductive Strategies

• Bivalve reproduction typically involves separate sexes.
• Notable larval stages include the trochophore stage and the veliger stage, where shell formation begins.
• Reproduction events often involve mass release of eggs into the water.

Shell Characteristics

• Shell shape varies, with forms including irregular, elliptical, wedge-shaped, fan-shaped, and more, which are used for taxonomic identification.
• Shell sculpture varies with features such as nodular radial ribs and smooth surfaces, also utilized for classification.

Subclassifications

• Subclass Heterodonta is the largest group of bivalves and is mainly marine.
• Subclass Protobranchia consists mostly of deep-sea bivalves.

Ecological Roles

• Bivalves are significant food sources (e.g., oysters, clams, scallops) and play a crucial role in aquatic ecosystems by filter-feeding, which helps clean water.
• Oysters provide habitat structures, promoting biodiversity.

Invasive Species

• Zebra and brown mussels are invasive bivalve species known to cause economic damage.
• Zebra mussels can over-filter water, depleting plankton populations in certain regions.

Unique Features

• Pearls form as foreign bodies are encysted within layers of shell material.
• Bivalves possess a crystalline style in their stomach, which aids in digestion through mechanical and enzymatic processes.