Size

Mo with the largest Dardanus megistos in a baler shell (Melo amphora). Photo Maria Anselmo, Heron Island, 2012

Dardanus megistos can reportedly reach 30cm in length. Larger individuals are often found at greater depths (Tudge 1995) and specimens collected from the reef flat of Heron Island as part of this project were much smaller than this. No very small individuals were found, although it is unknown whether all hermit crabs had reached sexual maturity. A single large individual was discovered. Housed in a large baler shell, Melo amphora, this specimen recorded a gross weight (shell included) of 1019 grams.

Sexual dimorphism, with males being larger, is common amongst decapods (Turra 2004), has been recorded in several species of hermit crab (Macphersen and Raventos 2004, Litulo 2005) but is not apparent in others (Macphersen and Raventos 2004). Dimorphism in hermit crabs has been hypothesised to be driven by observed differences in growth rate, which may be explained by the investment in eggs by females (Bertness 1981). However, in many animals, such dimorphism arises from a strong sexual selective pressure. Larger, stronger males have an advantage when fighting for the right to mate. This appears to hold for hermit crab; males of most species typically mate only with females smaller than themselves and larger males usually win male-male fights over mating rights (Hazlett 1972).

Males of a related species, D. deformis, were found to be consistently larger than females from a population in Mozambique (Liluto 2005), showing that at least some hermits of Dardanus are sexually dimorphic. However, two sympatric species within the genus Anapagurus were examined by Macphersen and Raventos (2004) and one was found to be sexually dimorphic while the other wasn't.