New Zealands micro crab

[nomad fish]

Amarinus lacustris

• Ease of care: Experienced to advanced 
• Conservation status: Unknown 

A species of freshwater crab from Australia, New Zealand and nearby islands, where it lives in water of various salinities. It grows up to 10 mm (0.4 in) wide, with an H-shaped groove on its back. It is an omnivore and is eaten by crayfish and fish. It was first discovered in Lake Pupuke, near Auckland, and is the only freshwater crab in New Zealand.

A. lacustris grows to a maximum size of 10 millimetres (0.39 in) across the carapace, with a leg span of 20 mm.[5][6] The carapace is grey-brown and almost circular, marked with a set of grooves forming an H-shape with the two uprights bending outwards, and the whole animal is covered in setae.[7]

Living in estuarine, freshwater and shallow subtidal habitats, usually in salinities of 1–6‰, but occasionally to 0.1–9.6‰.[3] It can be found living amongst detritus and vegetation in the shaded edges of rivers and lakes.[6] Remains of both animals and plants have been found in the gut contents of A. lacustris, indicating an omnivorous diet.[7] Its predators include crayfish and introduced trout.