Geukensia demissa, (Dillwyn, 1817)
Geukensia demissa is a species of mussel, a marine bivalve mollusk in the family Mytilidae, the true mussels. This species is native to the Atlantic coast of North America. The common names for this species include ribbed mussel, Atlantic ribbed marsh mussel and ribbed horsemussel. However, the common name ribbed mussel is also used for the Southern Hemisphere mussel Aulacomya atra. The appearance of the shell is grooved and oval in shape. The interior of this mussel is tinted purple.
The ribbed shells of this species usually attain a length of 10 cm length, and can be as large as 13 cm. Age can be determined by counting dark growth rings on the shell and mussels typically live 10 – 15 years, but more advanced ages are not uncommon.
The ribbed mussel occurs in the coastal waters of salt marsh habitats from the southern Gulf of St. Lawrence in eastern Canada, south along the western Atlantic coast to Florida. In the Gulf of Mexico this species is replaced by the southern ribbed mussel, Geukensia granosissima, and the two species hybridize in southern Florida.
The ribbed mussel has been introduced to Texas, Mexico, California, and Venezuela.
The ribbed mussel is a filter feeder, who consumes microalgae, bacteria, and nanoflagellates.
The speed at which ribbed mussels feed changes with temperature which is partially due to the availability of their food, and they feed more when their environment is warmer. Location also plays a role in filtration rates due to food quality and availability.
Ribbed mussels are dioecious and sexes can only be determined histologically.
They reproduce once per year in Connecticut and South Carolina, however in an introduced population in Venezuela two spawning peaks have been observed.
Mussels >15 mm are typically reproductive; however, it is not uncommon for mussels up to 35 mm to have no signs of gametogenesis. Their location in the salt marsh plays a role in when they become reproductive because edge ribbed mussels mature at smaller body sizes compared to other mussels.
Ribbed mussel larvae return to the marsh during recruitment, and they tend to settle near marsh edges where there are adult ribbed mussels.
Native Americans near the Jamestown settlement manufactured shell beads that were called "rawrenock" in the local Powhatan language. The production process involved grinding broken ribbed mussel shells into disk-shaped beads and drilling a central hole to string the jewelry with. Surviving examples were recovered from the refuse that filled an abandoned well within the James Fort.
No dive sites list Atlantic Ribbed Mussel yet. Explore the map to find sites near you.