Class Bivalvia

• • Pelecypoda
  • two-valved shells
  • laterally flattened body
  • Umbo - bulge at dorsal edge of bivalves comprising of the earliest material deposited by the animal
• 4 basic gill types of bivalves

  1. Protobranch - attached to each other by interfilamental ciliary junctions
  2. Filibranch - linked by ciliary disc junctions
  3. Eulamellibranch - junctions made of tissue rather than cilia
  4. Septibranch - lack filaments and form muscular septum

  
• Subclass Protobranchia

  • first gill
  • Yoldia and Nucula
  • Morphologically the primitive state of bivalve
  • bipectinate gills
  • deposit feeding
• Subclass Lamellibranchia

  • plate gill
  • clam, muscles, scallops
  • secretion of attachment byssal threads by byssal or byssus gland in the foot
• Subclass Lamellibranchia

  • Shipworms (Teredora malleolus)
  • With wood-storing caecum packed with symbiotic bacteria
  • Pallets analogous to operculum
  • Shell used to excavate the burrow
• Subclass Septibranchia/Anomalodesmata

  • fence gill/irregular ligament
  • also called "dipper shells"
  • Small group of carnivorous bivalves and on pieces of decomposing animal tissue
  • Ctenidium highly modified, lacking filaments and forming muscular septum perforated by ciliated openings
  • Feed as vacuum cleaners sucking on small crustaceans and annelids
  • Stomach lined with chitin
  • Small labial palps with no sorting function