The Planorbidae is a freshwater snail family of the subclass Pulmonata. These snails, although aquatic, are lung breathers. Gills are lacking; instead there is a large pulmonary sac for gaseous exchange. In the snail shown here, nearly half of the last whorl is occupied by the lung, clearly visible as an air-filled space. The Planorbidae are coiled in one plane, i.e., they are planate, a characteristic from which the family name is derived.

Segmentina hemisphaerula, top (umbilical) and bottom (inverted spire) views. Some species of the aquatic pulmonate snail family Planorbidae have calcified barriers partially closing the shell aperture. These can be seen as lighter-colored transverse bands showing through the shell on the right. The purpose of these barriers is to keep out potential predators.

Ancylastrum irvinae, from Tasmania. A limpet-like form has evolved independently numerous times in the Mollusca. This freshwater snail of Tasmania is most closely related to Australian members of the family Planorbidae.

Helisoma anceps has a wide distribution in eastern North America, but H. royalense is known only from Isle Royal, Michigan.

Three species of the genus Planorbella in Michigan. Planorbella campanulata has a wide distribution in northern North America, but P. multivolvis is known from only one locality and P. smithi is known from only two lakes. Planorbella multivolvis is already extinct, and P. smithi is endangered.

Bulinus truncatus, from North Africa. This species is the snail intermediate host for Schistosoma haematobium over much of Africa and the Near East. Schistosoma haematobium is the causative agent for vesicular or urinary schistosomiasis.

Copulation in Bulinus is similar to that of Radix, shown above, except that Bulinus is sinistral while Radix is dextral. Here the albino snail (red colored because of its red, hemoglobin-containing, blood) will first act as male and the black pigmented snail will act as female. Note the large bubble of air in the lung of the albino snail.

The albino snail is probing with its penis/preputium for the female gonopore of the pigmented snail.

Copulation. After completion, the mating partners with change positions, and copulate once more, with the pigmented snail acting as male and the albino as female.


bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature