Common rock crab

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Common rock crab
Rock crab on tunicate colony of Didemnum
Rock crab on tunicate colony of Didemnum
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Family: Varunidae
Genus: Hemigrapsus
Species: H. sexdentatus
Binomial name
Hemigrapsus sexdentatus
(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 the eggs change colour from light brown to transparent.

Synonyms: Hemigrapsus edwardsi, Hemigrapsus edwardsii

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