The valves of Rangia cuneata are thick and heavy, with a strong, rather smooth pale brown periostracum. The shells are equivalve, but inequilateral with the prominent umbo curved anteriorly. An external ligament is absent or invisible, but the dark brown internal ligament lies in a deep, triangular pit immediately below and behind the beaks. Both valves have two cardinal teeth, forming an inverted V-shaped projection. The upper surface of the long posterior lateral teeth (LaSalle and de la Cruz 1985) is serrated. The inside of the shell is glossy white, with a distinct, small pallial sinus, reaching to a point halfway below the posterior lateral. The pallial line is tenuous (Garcia-Cubas 1981).
In the USA, Rangia cuneata has two spawning periods ranging from March-May and late summer-November in Louisiana (Fairbanks 1963) and February-June and September-November in Mexico (Rogers and Garcia-Cubas 1981), although in both areas, spawning may be continuous. Cain (1975) found that gametogenesis was initiated when the water temperature rose above 15 °C and with salinities above 0 PSU or below 15 PSU (Hopkins 1970).
Rangia cuneata inhabits low salinity estuarine habitats (Parker 1966) and is as such most commonly found in areas with salinities from 5-15 PSU (Swingle and Bland 1974). R. cuneata possess both extracellular (blood and body fluid) and intracellular mechanisms of osmoregulation, which enables them to respond to sudden salinity changes in many estuaries (Bedford and Anderson 1972). They can cross the 'horohalinicum', the 5-8 PSU salinity boundary which usually divides fresh and salt-water invertebrates, making them one of the few freshwater clams to become established in brackish water (Ladd 1951) as such thriving in a zone unfavourable for many animals. Competition and predation may explain its scarcity in high salinity environments (Cooper 1981). A combination of low salinity, high turbidity and a soft substrate of sand, mud and vegetation appears to be the most favourable habitat for R. cuneata (Tarver 1972). Although larvae prefer coarser sediment for settlement, adults are often found in muddy sediments (Fairbanks 1963; Cain 1975; Jordan and Sutton 1984).
Principal source: Verween, Annick., Francis Kerckhof., Magda Vincx and Steven Degraer., 2006 First European record of the invasive brackish water clam Rangia cuneata (G.B. Sowerby I, 1831) (Mollusca: Bivalvia) Aquatic Invasions (2006) Volume 1, Issue 4: 198-203;
Pfitzenmeyer H. T and Drobeck K. G 1964. The Occurrence of the Brackish Water Clam, Rangia cuneata, in the Potomac River, Maryland;
LaSalle MW and de la Cruz AA 1985. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Gulf of Mexico): common rangia.
Compiler: Dr. Annick Verween, Marine Biology Section, Department of Biology University of Gent. Belgium
Publication date: 2005-04-08
Recommended citation: Global Invasive Species Database (2023) Species profile: Rangia cuneata. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=1156 on 02-12-2023.