Common name : pen shells or fan shells

Aspect : large, thin and triangular or fan-shaped; valves inequilateral, elongated, with the broad posterior end gaping widely; surface frequently scaled or spinose and dark brown to black colored; hinge edentulous (no teeth); length typically 15–30 cm; some species reach 50–90 cm (e.g., Pinna nobilis up to 120 cm in extreme cases)

Feeding : filtration of microorganisms in suspension (phytoplankton, zooplankton, detritus, and organic particles)

Environment : worldwide in warm-temperate to tropical seas from lower intertidal to about 100 m depth (most common 5 to 40 m); shell buried partially (1/3) vertically or obliquely in soft substrates (sand, muddy sand, seagrass beds, coral rubble); anchored firmly by a very strong, thick byssus (often the strongest byssus of any bivalve used to make “sea silk”)