Species Description: Isognomon alatus is a member of the family Isognomonidae. Its shell is fan-shaped appearing extremely compressed and thin-walled. The hinge is straight and elongated (Siung 1980). The color of the flat tree oyster is usually drab greenish white to purple-black with flaky co-marginal lamellation (i.e. thin layers or plates). The interior of the shell (nacre) is yellowish with a purple-brown stain. The border is darker (Mikkelsen and Bieler 2008). The soft body of the animal is oval and covered by an opaque mantle (Siung 1980).
Regional Occurrence: The flat tree oyster is found only in the tropical regions of the Atlantic Ocean and Gulf of Mexico (Hall 1985). Isognomon alatus occurs from central Florida to Bermuda, the Bahamas, West Indies, Caribbean Central America, and as far south as Brazil (Mikkelsen and Bieler 2008). It is generally found along the sub-tidal and intertidal surfaces of mangrove roots, in particular the red mangrove tree (Rhizophora mangle L.) (Siung 1980, Hall 1985).
IRL Distribution: Isognomon alatus is common on the mangrove roots in the Indian River Lagoon.
Age, Size, Lifespan: Adult flat tree oysters range from 75 mm to 95 mm in length (Mikkelsen and Bieler 2008). The shells of Isognomon alatus usually grow 4-5 cm in height, individuals as large as 9 cm have been encountered (Siung 1980).
Abundance: In a study of the fouling community of the Loxahatchee River Estuary south of the Indian River Lagoon in Florida, Isognomon alatus was reported to be abundant in areas with highest salinities (McPherson et al. 1984).
Reproduction: Isognomon alatus participates in mass spawning events, peaking after the onset of high rains when the salinity of seawater is lower (Siung 1980).
Embryology: The prodissoconch planktonic larvae of the flat tree oyster are approximately 210-237µ wide and 260-280µ long just prior to settlement. After settlement and subsequent attachment by byssal threads, the shell extends around the prodissoconch (Siung 1980).
Temperature: There have been no specific studies of the temperature tolerance for Isognomon alatus, however experiments investigating the effects of temperature on heart rate suggest normal physiological function between 25 and 35°C (Hall 1985).
Salinity: There have been no specific studies of the salinity tolerance for Isognomon alatus.
Trophic Mode: The flat tree oyster is a filter feeder, using its gills to remove plankton and detritus from the water column.
Hall JG. 1985. The adaptation of enzymes to temperature: catalytic characterization of glucose phosphate isomerase homologues isolated from Mytilis edulis and Isognomon alatus, bivalve molluscs inhabiting different thermal environments. Molecular Biology and Evolution 2:251-269.
ITIS. Integrated Taxonomic Information System. Available online.
McPherson BF, Sonntag WH, and M Sabanskas. 1984. Fouling community of the Loxahatchee River Estuary, Florida, 1980-1981. Estuaries 7:149-157.
Mikkelsen PM and R Bieler. 2008. Seashells of Southern Florida. Princeton University Press, Princeton, NJ. pg. 98-99.
Siung AM. 1980. Studies on the biology of Isognomon alatus Gmelin (Bivalvia: Isognomonidae) with notes on its potential as a commercial species. Bull. Mar. Sci. 30: 90-101.
Trueman ER and GA Lowe. 1971. The effect of temperature and littoral exposure on the heart rate of a bivalve mollusc, Isognomon alatus, in tropical conditions. Comp. Biochem. Physiol. 38A: 555-564.