Freshwater Molluscan Shells
Hydrocenidae, Valvatidae, and other freshwater snails
Minute amphibious snails classified with the old archeogastropoda, native to eastern and southern Asia, and southern Europe. One species is listed for southern Africa by Pilsbry and Becquaert (1927) "[They] are more or less amphibious dwellers in wet vegetation, clinging to the faces of rocks continually washed by the spray from waterfalls" (Preston, 1915). He lists eight species for the Indian subcontinent
Georissa japonica Pilsbry, 1900. x8. Japan
Small wide-spired operculate snails, commonly refered to as valve snails, egg-laying and hermaphroditic. Burch (1982) lists 11 North American species. 11 are also listed for the former USSR by Zhadin (1952) while only two are listed for India, and one for Africa. Banarescu includes the following genera;
Valvata; (several subgenera listed by both Banarescu and Burch) throughout Europe, northern Asia, and North America.
Borysthenia; Eastern and central Europe.
Gagea; Endemic in Lake Ohrid.
They have a featherlike gill, visible on the left side outside the shell when the snail is active (Brown, 1991), and a ciliated pallial tentacle extending out to the right. Please see the Animal Diversity Web http://animaldiversity.ummz.umich.edu/site/accounts/information/Valvatidae.html or http://www.allesumdieschneck.de/html/valvatidae.html for pictures of living Valvata snails. Dillon (2000) says of this little studied group, that some researchers have reported filter-feeding behaviour, while others have concluded they are strictly grazers. Shell characteristics may be variable. For instance the species V. tricarinata occurs in forms having differing numbers and locations of spiral carinae or angulations. Several such forms may occur within a single population (William Heard, in Burch, 1982).
Valvata stenotrema (Polinski) Lake Ohrid, Macedonia. x8.
Valvata bicarinata Lea 1841 American midwest and northeast. x8.
Megalovalvata demersa (Lindholm, 1909) Lake Baikal. x8.
A few members of this marine or brackish water family have adapted to fresh waters. Most inhabit marginally marine environments in the tropics.
(Linnaeus, 1758) Brandt
(1974) indicates this is a snail
of "muddy irrigation trenches,
drainages and swamps in the
mud flats." Native to much of
(Gmelin, 1790) Native to
Thailand. This image,
and the photographs
below are from Brandt (1974).
Carniverous gastropods related to the marine whelks. Two freshwater genera, Clea and Afrocanidia.
Brandt (1974) describes and pictures six Clea (subgenus Anentome) species, but could only confirm Clea helena for the territory of Thailand. He says of Clea helena that it is the only species in Thailand that is "not restricted to running water as it is also found in lakes and ponds", and that it "feeds predominantly on decaying protein, but has been observed to attack living snails and worms."
Clea has been offered for sale in the pet trade and the possibility exists for it to become invasive. Harry Lee includes this and other information on the genus at http://www.listserv.uga.edu/cgi-bin/wa?A2=ind0712B&L=conch-l&P=R722&D=1&H=0&O=T&T=1. He also posted a listing of species at http://www.listserv.uga.edu/cgi-bin/wa?A2=ind0712B&L=conch-l&P=R1895&D =1&H=0&O=T&T=1.
Clea helena (Philippi, 1847) (Left)
Widespread, Southeast Asia, Indonesia.
Clea scalarina (Deshayes, 1876) (Right)
Mekong River. Slightly magnified.
Nassa mudsnails, characteristic of tidal
mudflats, have also invaded fresh waters.
Banarescu (1990) mentions
Pygmaenassa - India,
Nassodonta - East Asia, and
Arcularia - Lake Chilka, Burma.
(Wattebled, 1886) Viet Nam.
Photo Bill Frank, webmaster
Rivomarginella morrisoni Brandt, 1968. x4
Rivers, lakes, and canals along the Gulf of Thailand. One
freshwater species "Known from Thailand only" (Brandt, 1974).
Morrisonietta siamensis Brandt, 1968. x10
Prefers brackish water of low salinity. Several species endemic
to various localities in Southeast Asia (Brandt, 1974).