This large and varied family of freshwater gastropoda is by virtue of its having two species (V. viviparus (L.) and V. contectus (Millet)) living in English rivers, well known to British collectors. The Viviparidae enjoy an almost world-wide distribution, being found on all the continents except S. America and Antarctica. It is divided into two subfamilies. Viviparinae, inhabiting Europe, Asia Minor, northern Asia and N. America, and Bellamyinae in Africa, tropical Asia and Australia. They differ in the male sexual gland, which is interwoven with the digestive gland in the Viviparinae, but free from it in the Bellamyinae. Furthermore the embryonic whorls of the shell are band¬ed in the former, but not in the latter.
The only common major factor in their distribution is through water channels and some have been introduced by man, e.g. Bellamya malleata (Reeve) a large Japanese species, into the Western United States. Low temperature may play an important part in their distribution as it exists at present, but beyond the fact that they do not occur in the Polar regions, there is apparent¬ly no definite observation on the influences of this factor.
As the name suggests, the family is viviparous and according to some authors ovo-viviparous. The sexes are separate. They are operculate, having a horny or semi-calcareous operculum. Respiration is entirely aquatic and is performed by means of a ctenidium. Food consists of aquatic plants, algae, etc. They occasionally become carnivorous. In many countries where they occur, these snails are used as food by man and domestic animals.
Distribution: Europe. In Europe these snails do not extend their range beyond lat. 50 N. in Scandinavia and this appears to be their northern limit also in Russia. In Asia Minor they extend to about 30 E. Only one species is found south of the Appenines and none are known from the Iberian Peninsular. Bourguignat divided the European species into 7 sub-groups and no less than 50 species! Kobelt however recognised only two main types, V. viviparus and V. contectus.
America. None are known living either in Central or South America. One small isolated species, V. Germondiana (Orb), occurs in Cuba.
In North America there are besides Viviparus s.s. four endemic genera, Tulotoma Haldeman, Campeloma Rafinesque, and Lioplax Troschel. The two common European species have been introduced into the eastern states and two Japanese species into the western seaboard.
Asia. None are found in the greater part of Asia Minor, Arabia, Afghanistan, Tibet, the whole of central Asia, Mongolia, the greater part of China, and with the exception of the Amur Basin, the whole of Asiatic Russia.
In India, the Bellamya bengalensis group is common and widely distributed, whilst the Chinese species B. chinensis and the Japanese, B. malleata and B. japonica are among the largest forms known. A small smooth unbanded species B. ;javanica is typical of the Bellamya found throughout the Philippines and the Greater Sunda Islands, although Lake Lanas on the Philippine island of Mindaneo has a number of peculiar endemic species.
Australia. Known only from Northern Territory, Queensland and parts of eastern Australia. A very unusual form (B. fragilis Preston) with a strongly keeled and paper-thin shell, has been described from New Guinea, living 80001 up in the Central Arfak Mountains.
Africa. Bellamya is widely distributed in tropical Africa. The typical form is B. unicolor (Olivier) which is found fossil in deposits of Miocene age and is now found living in all the great lakes and major river systems. In Lake Tanganyika the large and striking genus Neothauma is common and another species N. ecclesi has recently been discovered in Lake Nyasa. Numerous sub¬species of B. unicolor have been described from Lake Victoria. Lake Minerva has a very distinct species, perhaps allied to Neothauma.
Fossil Viviparidae. Many fossil species, attributed to this family have been described, especially from rocks of Caenozoic age. The earliest fossil records are from Jurassic strata of the Inferior Oolite (Bajocien). The record of a supposed form of Viviparus (V. carbonarius Garwood) from the Carboniferous of Yorkshire is undoubtedly based on incorrect identification. It is also now considered most unlikely that the Jurassic species (V. scoticus Tate) was correctly referred to this family. From the Cretaceous onwards, however, there is no doubt that members of this family became definitely separated from the ancestral marine and estuarine forms and took to a freshwater life.
The first extensive occurrence of Viviparidae, and one which can without any doubt be assigned to the family, is that of the Purbeckian forms of Upper Jurassic age and those found in the Wealden strata of Lower Cretaceous age, in south west England. Three species form the main constituents of the famous Purbeck Marbles.
During the Tertiary many species were living in most parts of the world. In Britain, the Bembridge Beds of Oligocene age, in the Isle of Wight contain several species of which V. lentus (Solander) is typical. This species is also found in the Woolwich Beds of Lower Eocene age.
The magnificent series of Viviparus found in the Pliocene of Slavonia have attracted attention from early times and the literature on them is very extensive. They have been frequently referred to in studies on evolution. The highly sculptured and otherwise specialised species of the Pliocene lakes of Eastern Europe had been produced under very favourable lacustrine conditions and were not able to adapt themselves to the changing conditions, and all perished without leaving any descendants whatsoever. The less specialised smooth-shelled species persisted and spread over the entire area, giving rise to such species as V, diluvianus (Kunth) found in Pleistocene deposits in Britain and still living on the continent, and V. medius (Woodward), and finally to V. viviparus (L) and V. contectus (Millet). Widely distributed over this area today.
Elsewhere fossil Viviparidae are found in countries where the family is still living, the exception being South America, where the discovery of a true Viviparus in Upper Cretaceous deposits in Brazil and another from beds of Tertiary age in Chile, suffice to prove that the family was represented there at least until the Early Tertiaries. The causes which lead to its extinction are uncertain, as other freshwater molluscs like the Ampullariidae still live there. Possibly the flooding over the area in which the family flourished by the sea was responsible for its disappearance.
T. Pain D. Beatty