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'
On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection paper, consisting of the letter and papers, was published in the "Zoological Journal of the Linnean Society 3" (20 August): 46–50. The paper consisted of a communication letter by Joseph Dalton Hooker and Charles Lyell dated 30 June 1859, giving information on the three sections of the papers. The introduction is shown below, along with the section headings: MY DEAR SIR,—The accompanying papers, which we have the honour of communicating to the Linnean Society, and which all related to the same subject, viz. the Laws which affect the Production of Varieties, Races, and Species, contain the results of the investigations