Species Description: Brachidontes exustus is a member of the family Mytilidae. It has a thin, fan shaped shell with fine divercating radial ribs. The ribbed surface of the shell is most evident at the outer edges. Umbones are present at the extreme anterior end. The shell can range from blue-gray to yellow to dark brown. The interior has purple-brown blotches with one to four small purplish dysodont hinge teeth (Abbott and Morris 2001, Mekkelsen and Bieler 2008).
Species designations in the genus Brachidontes are currently under revision (Berquist et al. 2006). A recent study of the Brachidontes exustus species complex in Florida suggests that there are four cryptic populations with distinct genetic profiles (Lee and O Foighil 2004).
Regional Occurrence: Brachidontes exustus occurs in the intertidal on rock surfaces. The scorched mussel has been recorded from New Jersey to Florida, Bermuda, Bahamas, West Indies, Gulf of Mexico, Caribbean Central America, South America to Argerntina, and St. Helena (Mekkelsen and Bieler 2008). It is commonly found washed ashore in clusters attached to other shells and seaweeds.
IRL Distribution: Brachidontes exustus is commonly associated with oyster reefs in the Indian River Lagoon.
Age, Size, Lifespan: The scorched mussel grows to 10 - 46 mm in length (Mekkelsen and Bieler 2008).
Abundance: Brachidontes exustus is often the dominate mollusc in estuaries and mangrove roots (Barber et al. 2005).
Reproduction: The scorched mussel is gonochronistic, having separate sexes. In a study of populations from Tampa Bay, Florida, the ratio of males to females is reported to be nearly 1:1. Brachidontes exustus has two spawning periods in the spring, between March and April and, in the fall, between September and November (Barber et al. 2005).
Embryology: The embryology of the scorched mussel has not been well studied. However, other members in this family, such as Lithophaga bisulcata, Mytilus edulis, and Perna perna, have been well studied. The larvae of mytilid mussels appear to quickly develop into veligers followed by pediveligers (competent larvae) within a few weeks (Siddall 1980, Scott 1988a and b). Metamorphosis of the pedivleiger occurs once an appropriate area to settle is encountered (Siddall 1980, Scott 1988a).
Temperature: Brachidontes exustus has a broad temperature tolerance. Its spawning periods correlate with changes in sea water temperatures. Spawning occurs in the spring when the sea water temperatures increase and in the fall when sea water temperatures decrease. Gametogenesis appears to decrease in the scorched mussel during the colder winter months (Barber et al. 2005).
Salinity: Adult Brachidontes exustus appear to have a high tolerance for changes in salinity (Barber et al. 2005, Berquist et al. 2006).
Trophic Mode: Brachidontes exustus are filter feeders (RiisgŒrd 1988).
Abbott RT and PA Morris. 2001. A Field Guide to Shells: Atlantic and Gulf Coasts and the West Indies pg. 17.
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Barber BJ, Fajans JS, Baker SM and P Baker. 2005. Gametogenesis in the non-native green mussel, Perna viridis, and the native scorched mussel, Branchiodontes exustus, in Tampa Bay, Florida. Journal of Shellfish Research 24:1087-1095.
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Lee T and D O Foighil. 2004. Hidden Floridian biodiversity: mitochondrial and nuclear gene tree reveal four cryptic species within the scorched mussel, Branchiodontes exustus, species complex. Marine Ecology 13:3527-3542.
Mikkelsen PM and R Bieler. 2008. Seashells of Southern Florida. Princeton University Press, Princeton, NJ. pgs. 84-85.
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