Select the search type
  • Site
  • Web




Calcinus guamensis 
Guam Hermit

Monica Pelcar




Fact Sheet



Physical Description


Life History & Behaviour

Anatomy & Physiology

Evolution & Systematics

Biogeographic Distribution

Conservation & Threats

References & Links



C. guamensis is a tropical hermit crab which inhabits areas below the reef slope such as, intertidal and shallow subtidal zones to depths of 20m (Hogarth et al. 1998). Individuals like to assemble on branches of living coral, and the specimens discovered for this report were found on coral reefs however they inhabit a wider range of areas on the reef. The places include; littoral areas, sublittoral areas, amongst coral rubble, and rocks (Hogarth et al. 1998; Shih & Yu 1995). C. guamensis is found to inhabit numerous species of small gastropod shells. These include; Morula spp., Conus spp., and Drupa spp. (Morgan 1991; Shih & Yu 1995).  ​  

Most species of hermit crab are considered to be omnivorous detritivores (Hazlett 1981). They are essentially scavengers, who get most of their nutrients from feeding on both living and dead macroscopic pieces of animals (Hazlett 1981). But can also get nutrients through filter feeding and when need be they can be opportunistic feeders (Lancaster 1988).


Utilising a shell as a mobile home reduces the number of natural predators a hermit crab has. Without their shell they would otherwisebe extremely vulnerable to a wide array of predators but because of their shell only a few specialist predators are able to prey upon them. Hermit crabs are generally preyed upon by shell crushing crabs, teleost fish, birds, octopuses and other invertebrates (Bertness 1981). Hermit crabs shells are their biggest defense against their predators, however they employ escape responses. When they sense, for example, and incoming fish they will retreat and fall into rock or coral crevices which is inaccessible to predators (Bertness 1981). Predation pressure on hermit crabs influence their distribution pattern, shell selection, and behaviour (Bertness 1982). In areas of low predation the need for an optimal shell is in less demand than in areas of high predation, as hermit crabs are less likely to utilise their shell when predators are absent (Conover 1978). The opposite is true for crabs that inhabit areas of high predation; the need for an optimal shell is in high demand as it is much needed (Conover 1978).