[1] This species commonly grows 1 to 2 metres long and 5 to 7 mm wide.

It does not contract significantly when physically contacted or killed.

When it does actually contract strongly, it has a flattened appearance, being widest immediately behind the back of the head.

The part of the body containing the intestines is flat and broad.

[2] Baseodiscus mexicanus is found in abundance on the Pacific east coast in the waters of Panama and Mexico, as well as in the Galapagos Islands.