Tunnelling mud crab
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| Helice crassa (Dana, 1851) |
The tunnelling mud crab, Helice crassa, is a marine large-eyed crab of the family Grapsidae, endemic to the sea coasts of New Zealand. Their carapace width is up to 40 mm.
The tunnelling mud crab is common on mud flats, where they burrow. They are active by day and sleep by night, often closing their burrows with a plug of mud. As they are constantly preyed upon by birds and many other animals, their survival depends on how quickly they can withdraw into their burrows. They must also return frequently to their burrow to wet their gills.
The tunnelling mud crab has two short stalked eyes. Coloration is brownish, with older specimens becoming greenish orange. They feed by filtering out diatoms, algae and bacteria from the rich mud which is their habitat. Predators include parore, cod, flounder, yellow-eye mullet, and eels.
Females are 'in berry' in early spring and summer (August to March), carrying about 16,000 eggs of 0.3 mm, which change colour from brownish-yellow to transparent green during 42 days of incubation. Females may reproduce more than once per season, and do not require to mate again for this.
