: They breathe through plate-like gills (ctenidia) located in the mantle cavity.
: The nervous system is simplified, consisting of three pairs of ganglia. Ecological and Economic Importance : They breathe through plate-like gills (ctenidia) located
For further study and visual aids, students can refer to educational platforms like Yaklass or watch lesson summaries on YouTube . a middle calcareous layer
: Unlike gastropods (snails), bivalves lack a distinct head. Their body consists of a torso and a muscular "foot" used for burrowing or anchoring. and an inner pearly layer (nacre).
: The body is laterally compressed and enclosed in a bilateral shell. This shell consists of three layers: an outer organic layer (periostracum), a middle calcareous layer, and an inner pearly layer (nacre).