The given question asks which one of the following gastropod genera displays sinistral coiling. Let's analyze the options to find the correct answer.
- Physa: This is a genus of small, air-breathing freshwater snails. Notably, most species within the genus Physa exhibit sinistral or left-handed coiling of their shells. Sinistral coiling means that the shell of the snail spirals or coils to the left.
- Cypraea: Known commonly as cowries, this genus typically shows dextral (right-handed) coiling in their shells, which is the opposite of sinistral coiling.
- Murex: This genus contains many predatory tropical sea snails. Similar to Cypraea, most species of Murex show dextral coiling.
- Conus: This is a genus of predatory sea snails commonly referred to as cone snails. They generally exhibit dextral coiling as well.
Based on the above details, the correct answer is Physa since this genus is known for its sinistral coil shells. The remaining options, Cypraea, Murex, and Conus, predominantly display dextral coiling.