Modiolus (Modiolus) modiolus (Linnaeus, 1758)
Common name(s): Horse mussel, bearded mussel, fan mussel, giant horse mussel, northern horsemussel
|Modiolus modiolus from 100 m depth, San Juan Channel|
|(Photo by: Dave Cowles 7-2004)|
How to Distinguish from Similar Species: M. rectus is about 3x as long as wide and not likely found north of California. M. senshousia is smaller--up to 3 cm long and its periostracum is greenish.
Geographical Range: Atlantic and Pacific oceans, from the Arctic to subtropics
Depth Range: Usually subtidal. Occasionally intertidal (mostly on the underside of rocks)
Habitat: Muddy bottoms with shell hash.
Biology/Natural History Predators include the sunflower star Pycnopodia helianthoides. May have a symbiont, the pea crabs Fabia subquadrata or Opisthopus transversus. M. modiolus tends to form aggregates attached to one another and to empty shells.
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O'Clair and O'Clair, 1998
Carrington, Emily, Gretchen M. Moeser, Sean B. Thompson, Laura C. Coutts, and Carrie A. Craig, 2008. Mussel attachment on rocky shores: the effect of flow on byssus production. Integrative and Comparative Biology 48:6 pp 801-807
The periostracum is shiny, and hairy near the posterior end. This individual, found at Padilla Bay, also has byssal threads hanging out.
Side (ventral) view of the same individual as above.
This individual was riding on a float that washed up in Rosario Bay June 2012. Shell length is 9 cm. Photo by Dave Cowles, June 2012
This individual (the same one as above, found in Rosario Bay) had an unusual white "pearl" growth inside the hinge (see the growth to the left in the photo). This is likely due to an unusual irritation inside the shell of this individual and is not normally found in this species. Photo by Dave Cowles, June 2012
This individual, found on the same float as the individual above, had no "pearl" near the hinge. Shell length 8.8 cm, was a gravid female. Photo by Dave Cowles, June 2012