The mantle is the thin epithelial tissue that secretes the shell
and covers the musselís gills and visceral mass (i.e., central
large body containing major organs). Mantle tissue helps to
protect organs from soil abrasion and contamination. The mantle
is comprised of three layers: the outer, middle, and inner
folds. The outer fold secretes the shell, the middle fold is
sensory, and the inner fold (the thickest of the three) contains
the circular and radial muscles. The mantle forms two openings:
the inhalant (water entering) and exhalant (water exiting)
siphons. The space within the mussel that is filled with water
and lined by the mantle tissue is referred to as the mantle
cavity. The inhalant is the larger of the two siphons, typically
having 80 to 100 tentacles that aid in the filtration of food
particles. The exhalant siphon lacks tentacles and is located
just above (dorsal to) the inhalant siphon. The only other
opening in the mantle is the pedal gape, located on the ventral
surface of the shell; this is