Eurynolambrus australis

Eurynolambrus australis, commonly known as the triangle crab, and by its Māori name riangi, is a small species of crab that is widespread throughout New Zealand.

Triangle crab
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Infraorder:	Brachyura
Family:	Majidae
Genus:	Eurynolambrus
Species:	E. australis
Binomial name
Eurynolambrus australis H. Milne Edwards & Lucas, 1841

Habitat

E. australis is commonly found among stones and under rocks in the lower and sub tidal region of the intertidal zone where it can reach depths of up to 80 m. It is often found in rock pools with coralline turf.

Description

Adults are between 50 – 65 mm in size with a broad triangle-shaped carapace that extends over the leg base. This can be white, pink or bright red in colour with white, grey-brown, and yellow markings. Legs are short and flat with irregular crests. Their colour can be mottled with orange, dark red and white. They fold neatly underneath the carapace. Chelipeds have a rough and pitted surface and curve inwards. They are purple in colour with a white inner surface. The antennules are usually a pale yellow colour. The eyestalks are red.

Behaviour & Diet

The triangle crab is a scavenger feeder. It feeds mostly on coralline alga, which is thought to cause the bright red pigmentation on its shell. It also feeds on red and green algae, as well as amphipods, isopods and decapods.

It is a cryptic species that defends itself from predation with camouflage. Some divers and amateur observers suggest it is more active at night and may be nocturnal.