Species Description: Amygdalum papyrium is a member of the family Mytilidae. The fragile shell of the Atlantic paper mussel is white with a glistening, smooth periostracum (thin organic layer covering the outer layer of the shell) that is bluish green to yellow in color. The shell is elongate, compressed, and wider at the posterior end. Umbones are present near, but not at, the anterior end. The interior of the shell is iridescent white with smooth margins (Mikkelsen and Bieler 2008). A. papyrium attaches to the substratum as well as to each other with byssal threads often forming dense beds that support rich faunal and infaunal invertebrate assemblages.
Potentially Misidentified Species: Modiola arborescens not Dillwyn, 1817
Regional Occurrence: Amygdalum papyrium occurs in the North and South Americas from Maryland to Florida, and the Gulf of Mexico, and Venezuela (Mikkelsen and Bieler 2008).
IRL Distribution: The Atlantic paper mussel is common in the Indian River Lagoon.
Age, Size, Lifespan: The Atlantic paper mussel is short lived, living less than one year, and reaches sexual maturity within a few months (Walker et al. 2003). Amygdalum papyrium grows rapidly to a shell length of less than 32 mm. The largest shell reported for this species from Skidaway Island, Georgia is 39.5 mm. This specimen was collected in late March just before a large die-off. In the same population, there were more females than males.
Abundance: The abundance of Atlantic paper mussel was reported to range from 25 m2 to as high as 3325 m2 (Nassau River 1993), but can vary regionally. In the Indian River Lagoon, Amygdalum papyrium densities were reported from 25 m2 to as high as 525 m2.
Reproduction: The Atlantic paper mussel is a semelparous species, reproducing only once during its lifetime. This species is dioecious, having both males and females. The spawning period in a population from Skidaway Island, Georgia was reported to be between October and January with a few remaining ripe individuals found in February (R.L. Walker et al. 2003).
Embryology: The embryology of Amygdalum papyrium 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 pediveliger occurs once an appropriate area to settle is encountered (Siddall 1980, Scott 1988a). The larvae of A. papyrium stay in the water column for several weeks and recruit in the summer months (R.L. Walker et al. 2003).
Temperature: Low seawater temperatures less than approximately 12°C appear to trigger the mass mortality of Amygdalum papyrium (Walker et al. 2003).
Salinity: Amygdalum papyrium exhibit a high salinity tolerance, able to live in seawater with salinities of 45 ppt to less than 10 ppt (Walker et al. 2003).
Trophic Mode: Amygdalum papyrium is a filter-feeder.
Associated Species: Groups commonly associated with the Atlantic paper mussel beds are porifera (sponges), cnidarians (hydroids, corals and anemones), annelids (worms), crustaceans, other bivalves, bryozoans, and echinoderms (sea stars, sea urchins, and sea cucumbers).
American Museum of Natural History, Bivalves - Research, Training, and Electronic Dissemination of Data.
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Mikkelsen PM and R Bieler. 2008. Seashells of Southern Florida. Princeton University Press, Princeton, NJ. pg. 88-89.
NOAA National Benthic Inventory. Available online.
Scott PJB. 1988a. Initial settlement behavior and survivorship of Lithophaga bisculata (d'Orbigny) (Mytilidae:Lithophaginae). Journal of Molluscan Studies 54:97-108.
Scott PJB. 1988b. Distribution, habitat and morphaology of the Caribbean coral- and rock-boring bivalve, Lithophaga bisculata (d'Orbigny) (Mytilidae:Lithophaginae). Journal of Molluscan Studies 54:83-95.
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Walker RLT, Power RA and M Sweeney-Reeves. 2003. Observations on growth and gametogenesis of the Atlantic paper mussel, Amygdalum papyrium (Conrad 1846), from coastal Georgia. The Veliger 46:86-89.
Zip Code Zoo. Available online.