Common rock crab

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iCommon rock crab
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Family: Grapsidae
Genus: Hemigrapsus
Species: H. edwardsi
Binomial name
Hemigrapsus edwardsi
(Hilgendorf, 1882)

The common rock crab, Hemigrapsus edwardsi, is a marine large-eyed crab of the family Grapsidae, endemic to the sea coasts of New Zealand although not in the Chatham Islands or the southern islands. It grows to around 40 mm shell width.

This common intertidal crab occurs in a variety of habitat, under boulders, on the rocky reef, and on sand and mud flats. Coloration is a reddish purple, mottled with dirty white patches, with pale green antennules with dark red spots, but there are two colour types: light and dark. Darker crabs are marked with dark purple, sometimes almost purplish black, and their legs are banded.

Females are in berry from March to August, and they carry up to 26,000 eggs (size 0.3 mm) for about 6 weeks, during which time they change colour from light brown to transparent.

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