Amarinus lacustris
Amarinus lacustris is a species of freshwater crab from Australia, New Zealand and nearby islands, where it lives in water of various salinities. It grows up to 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.
Distribution
Amarinus lacustris is widespread in south-eastern Australia, from Tasmania to the Murray-Darling basin in South Australia and Victoria. It reaches as far inland as Lake Colac, Victoria.In New Zealand, A. lacustris is the only freshwater crab, and is found in a variety of habitats, including lakes, slow-flowing streams and larger rivers. It is found from the lower reaches of the Waikato River to Northland, with a notable population in the Oratia Stream near Auckland.
The species is also found on small islands in the Tasman Sea, such as Lord Howe Island and Norfolk Island, where it was first found at an altitude of "about 3,000 ft" on Mount Gower.
Description
Amarinus lacustris grows to a maximum size of across the carapace, with a leg span of 20 mm. 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.The closely related species A. paralacustris was separated from A. lacustris in 1970, but only mature females can be identified to the species level. The main difference between the two is that A. lacustris has "direct development", in which there are no free-living larval stages, whereas A. paralacustris has indirect development, including free-swimming larvae. Hatchlings are carried under the female's tail until they are large enough to feed independently.