Carcharhiniformes

thumb|253px|Ground sharks, like this blacknose shark, have a [[nictitating membrane which can be drawn over the eye to protect it.]]

The finback catsharks are a small family, the Proscylliidae, of ground sharks. They can be found in warm seas worldwide and are often the most numerous and common shark in tropical regions. They are generally less than 1 m in length, and are slow-moving predators that feed on bony fish and small invertebrates. Although some bear live young, the majority lay eggs with almost fully developed young; these egg cases, known as "mermaid's purses", are unique in appearance to each species.

Pentanchidae, the deepwater catsharks, is a family of sharks belonging to the order Carcharhiniformes. The deepwater catsharks are found in the Atlantic, Indian and Pacific oceans.