Geukensia demissa (Dillwyn, 1817)
Family: Mytilidae
Common names: Ribbed Horsemussel,  more...
Synonyms: Modiola plicatula Lamarck, 1819,  more...
Geukensia demissa image
Geukensia demissa  

Species Description: Geukensia demissa is a member of the family Mytilidae. The surface of the shell is grooved or ribbed and oval in shape. The ribbed mussel has a narrow blunt pointed head that is attached to submerged substrata. Shells are usually glossy, appearing olive-brown to brown-black, with some yellow to white on the outside and white on the interior with purplish tints.

Regional Occurrence: The ribbed mussel can be found along the Atlantic coast from the Gulf of Maine to Florida and the Gulf of Mexico (Franz 2001). It also reported from the San Francisco Bay on the West coast where it was introduced.

IRL Distribution: Geukensia demissa occurs in the Indian River Lagoon.

Age, Size, Lifespan: Adult Geukensia demissa can live for more than 15 years and grow to nearly 10 cm in length. The age of the ribbed mussel can be determined by counting the annual growth ribs on the shell (Brousseau 1982). Juvenile mussels can mature when they reach 12 mm.

Abundance: Geukensia demissa can be found among intertidal oyster reef clusters in numbers over 1,500 per m2 (Coen et al. 1999). Unlike oysters, ribbed mussels have the ability to reattach if dislodged, providing this species with more opportunities to respond to disturbance. Densities of 2000 up to 10,000 per m2 have been reported for this species in areas along the northern Atlantic coast.

Reproduction: Ribbed mussels have separate sexes and the sex can be determined by the color of the mantle. Females tend to be a medium brown whereas males are a yellowish-cream color. There is usually one annual spawn that occurs between June and September depending upon the region (Borrero 1987).

Temperature: The ribbed mussel is very hardy, tolerating short-term exposures to temperatures in excess of 45°C, but succumbing at temperatures above 45°C (Jost and Helmuth 2007).

Salinity: Geukensia demissa exhibits high salinity tolerance living in seawater at salinities less than 6 ppt and as high as 70 ppt.

Trophic Mode: Geukensia demissa are filter feeders that "pump" water over their gills where particles are either retained or passed into the digestive system. The ribbed mussel possesses large latero-frontal cirri that facilitate the retention of particles above 4 µ with a filtration rate measured in the laboratory to be 6.80 liters of seawater per hour (Riisgard 1988). Ribbed mussels are one of the few bivalves able to forage on small-sized bacterioplankton (Newell and Kambeck 1995, Kreeger et al. 1990).

American Museum of Natural History, Bivalves- Research, Training, and Electronic Dissemination of Data.

Borrero FJ. 1987. Tidal height and gametogenesis: reproductive variation among populations of Geukensia demissa. Biological Bulletin 173:160-168.

Brousseau DJ. 1984. Age and growth rate determinations for the atlantic ribbed mussel, Geukensia demissa Dillwyn (Bivalvia: Mytilidae). Estuaries and Coasts 7:233-241.

Coen LD, Knott DM, Wenner, Hadley NH, and AH Ringwood. 1999. Intertidal oyster reef studies in South Carolina: design, sampling and experimental focus for evaluating habitat value and function. Pages 131 156, In: MW Luckenbach, Mann R, and JA Wesson (eds.), Oyster Reef Habitat Restoration: A Synopsis and Synthesis of Approaches. Virginia Institute of Marine Science Press. Gloucester Point, Virginia.

Franz DR. 2001. Recruitment, survivorship, and age structure of a New York ribbed mussel population (Geukensia demissa) in relation to shore level - a nine year study. Estuaries 24:319-327.

ITIS Integrated Taxonomic Information System. Available online.

Jost J and B Helmuth. 2007. Morphological and Ecological Determinants of Body Temperature of Geukensia demissa, the Atlantic Ribbed Mussel, and Their Effects On Mussel Mortality. Biological Bulletin 213:141-151.

Kreeger DA, Newell RIE, and CJ Langdon. 1990. Effect of tidal exposure on utilization of dietary lignocellulose by the ribbed mussel Geukensia demissa (Dillwyn) (Mollusca:Bivalvia). Journal Experimental Marine Biology and Ecology. 144:85-100.

Newell SY and C Krambeck. 1995. Responses of bacterioplankton to tidal inundations of a saltmarsh in a flume and adjacent mussel enclosures. Journal of Experimental Marine Biology and Ecology 190:79-95.

Riisgard HU. 1988. Efficiency of particle retention and filtration rate in 6 species of Northeast American bivalves. Marine Ecology Progress Series 45:217-223.

Geukensia demissa image
Geukensia demissa  
Geukensia demissa image
Geukensia demissa