Cryptic species as defined by the Merriam-Webster dictionary are one of two or more morphologically indistinguishable biological groups that are incapable of interbreeding. By failing to distinguish these species as separate issues can arise when conducting biodiversity assessment and formulating wildlife management plans (McKenna, 2007).
African elephants are an example of a cryptic species. In 2001 a study revealed that there are two non-interbreeding, genetically distinct species: the African Bush Elephant and the African Forest Elephant. Bush elephants are larger and have outward curving tusks compared to forest elephants. Forest elephants have straight downward pointed tucks and are darker in color (World Wildlife Federation, n.d.).
World Wildlife Federation. (n.d.) Retrieved form http://worldwildlife.org/species/african-elephant
McKenna, P. (2007). Hidden species may be surprisingly common. Retrieved from http://www.newscientist.com/article/dn12293-hidden-species-may-be-surprisingly-common.html#.Um_57Wc4TLk
http://www.merriam-webster.com/dictionary/cryptic%20species
Here is another example of cryptic species.