Hermit crab on physical characteristics, genetic information, and combined data, support the longstanding hypothesis that the king crabs in the family Lithodidae are derived hermit crabs and should be classified as a family within Paguroidea. Other researchers have challenged this, asserting that the Lithodidae (king crabs) should be placed with the Hapalogastridae in a separate superfamily Lithodoidea. Six families are formally recognized in the superfamily Paguroidea, containing around 1100 species in total in 120 genera. The fossil record of "in situ" hermit crabs using gastropod shells stretches back to the Late Cretaceous. Before that time, at least some hermit crabs used ammonites'
Hermit (hummingbird) dimorphism usually associated with hummingbirds; green hermit is an exception to this rule. Hermits in the type genus, "Phaethornis", have a long decurved bill (three species, "P. koepkeae", "P. philippii" and "P. bourcieri", with virtually straight bills) with a red or yellow base to the lower mandible, and their two central tail feathers are elongated and tipped with white, buff or ochre. The crown of the head is flat, and two pale facial stripes enclose a dusky mask. Most hermits are restricted to the edge and undergrowth of forest, woodland and second growth, but some species (e.g. the planalto hermit)