Bellamya sp., from Australia. In the Viviparidae (so named because they give birth to small young snails rather than laying eggs), males lack a normal penis, but instead use a modified right tentacle, which is stouter and usually shorter than the normal left tentacle.


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