Marine Biology

Miner Hermit Crabs



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Miner hermit crab (Cancellus typus) are unusual crabs because they do not have a hardened carapace, nor do they find abandoned  mollusk or snail shells to claim as their own. These crabs make their home in hollowed out rocks which is why they are sometimes called rock hermit crabs. They move much slower than hermit crabs in shells but that is probably due to the fact that they must drag around their heavy rock homes which can be as large as ten centimeters. Although they are called miner hermit crabs they are not really “true” crabs.

False crabs

Miner hermit crabs belong to the Anomura family Diogenidae. That is, they do not have the four pairs of walking legs that other crabs have, hence the name false crab. They only have three pairs of walking legs while other false crabs may only have two pairs. The miner hermit crabs abdomen is soft and coiled which is why they need the protection of a rock, or in the case of the more common hermit crab, a shell. Based on which one of their claws is bigger is how the hermit crab is scientifically classified into families. The miner hermit crab has claws that are very similar in size so they can curl them up inside their rock for protection. Should a predator spot them, they have been known to abandon their rock and run for cover under stones or dive into holes, naked per say.

Habitat

The miner hermit crab is native to southern Australia. They are usually found intertidal under large stones and rocks but may be found deeper on land in rocky shorelines. These miner hermit crabs do not often dig their own holes but are thought to widen the holes of other crabs or the tube holes of the burrowing mollusk.   

Diet

Miner hermit crabs are for the most part scavengers. They feed on dead animal and plant matter. This is because of their speed and claw strength however, they will reach out and grab a slower creature should it get too close or be dying. Although their rock homes are adequate protection, they are usually found feeding after dark.  Due to miner hermit crabs being scavengers and cleaning up dead plant and animal matter, they are another important aspect of the ecosystem in which they live.

Conservation

Although rare, the miner hermit crab is not endangered… yet. Habitat loss is the biggest threat to these unusual creatures. Another threat is the introduction of invasive and non-native species to their habitat. Humans, of course, are a threat. These crabs do not do well as pets and should be observed rather than taken home. Beach development and nourishment are risking their habitat, as well as, dredging which causes fine sediment that is very harmful to the miner hermit crab and other shoreline and aquatic species.

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