Amarinus lacustris
Encyclopedia
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 10 mm (0.393700787401575 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.
, 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, including the lower reaches of the Waikato River
.
It 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" (900 m) on Mount Gower
.
. The carapace is almost circular and has a set of grooves forming an H-shape, with the two uprights bending outwards, and the whole animal is covered in seta
e.
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 larva
l stages, whereas A. paralacustris has indirect development, including free-swimming larvae.
of 1–6‰, but occasionally to 0.1–9.6‰. Remains of both animals and plants have been found in the gut contents of A. lacustris, indicating an omnivorous
diet. Its predators include crayfish
and introduced trout
.
in 1882, based on a single juvenile female collected from Lake Pupuke
on New Zealand
's North Island
. The species was later transferred to the genus Hymenosoma, and then to a new genus, Amarinus, in 1980. The name is derived from the Latin
meaning "not the sea", while the specific epithet means "of lakes".
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
from Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
and nearby islands, where it lives in water of various salinities. It grows up to 10 mm (0.393700787401575 in) wide, with an H-shaped groove on its back. It is an omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
and is eaten by crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
. It was first discovered in Lake Pupuke
Lake Pupuke
Lake Pupuke is a heart-shaped freshwater lake occupying a volcanic explosion crater between the suburbs of Takapuna and Milford on the North Shore of Auckland, New Zealand. The heart shape is a result of its formation by the linking of two circular craters - a larger one forming most of the lake...
, near Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...
, and is the only freshwater crab in New Zealand.
Distribution
A. lacustris is widespread in south-eastern AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, from Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
to the Murray-Darling basin
Murray-Darling Basin
The Murray-Darling basin is a large geographical area in the interior of southeastern Australia, whose name is derived from its two major rivers, the Murray River and the Darling River. It drains one-seventh of the Australian land mass, and is currently by far the most significant agricultural...
in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
and Victoria. It reaches as far inland as Lake Colac
Lake Colac
Lake Colac is situated to the north of the Colac town centre in Victoria, Australia. The lake provides a home for the Yacht Club, Rowing Club and water skiers during the summer months and has many birds. The foreshore has a playground, boat ramp and the Colac Botanical Gardens. Midway through...
, Victoria.
In New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, A. lacustris is the only freshwater crab, and is found in a variety of habitats, including lakes, slow-flowing streams and larger rivers, including the lower reaches of the Waikato River
Waikato River
The Waikato River is the longest river in New Zealand. In the North Island, it runs for 425 kilometres from the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the...
.
It is also found on small islands in the Tasman Sea
Tasman Sea
The Tasman Sea is the large body of water between Australia and New Zealand, approximately across. It extends 2,800 km from north to south. It is a south-western segment of the South Pacific Ocean. The sea was named after the Dutch explorer Abel Janszoon Tasman, the first recorded European...
, such as Lord Howe Island
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...
and Norfolk Island
Norfolk Island
Norfolk Island is a small island in the Pacific Ocean located between Australia, New Zealand and New Caledonia. The island is part of the Commonwealth of Australia, but it enjoys a large degree of self-governance...
, where it was first found at an altitude of "about 3,000 ft" (900 m) on Mount Gower
Mount Gower
Mount Gower dominates the southern tip of Lord Howe Island and has its peak at 875 metres .Average climbing time to Mount Gower's summit is 8 – 10 hours. The path is rope-assisted and rated as one of the world's best one-day hikes...
.
Description
A. lacustris grows to a maximum size of 10 millimetre (0.393700787401575 in) across the carapaceCarapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
. The carapace is almost circular and has a set of grooves forming an H-shape, with the two uprights bending outwards, and the whole animal is covered in seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....
e.
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 larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l stages, whereas A. paralacustris has indirect development, including free-swimming larvae.
Ecology
A. lacustris lives in estuarine, freshwater and shallow subtidal habitats, usually in salinitiesSalinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
of 1–6‰, but occasionally to 0.1–9.6‰. Remains of both animals and plants have been found in the gut contents of A. lacustris, indicating an omnivorous
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
diet. Its predators include crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
and introduced trout
Trout
Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
.
Taxonomic history
A. lacustris was first described (as Elamena lacustris) by Charles ChiltonCharles Chilton (zoologist)
Charles Chilton was a New Zealand zoologist, the first rector to be appointed in Australasia, and the first person to be awarded a D.Sc. degree in New Zealand.-Biography:...
in 1882, based on a single juvenile female collected from Lake Pupuke
Lake Pupuke
Lake Pupuke is a heart-shaped freshwater lake occupying a volcanic explosion crater between the suburbs of Takapuna and Milford on the North Shore of Auckland, New Zealand. The heart shape is a result of its formation by the linking of two circular craters - a larger one forming most of the lake...
on New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
's North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
. The species was later transferred to the genus Hymenosoma, and then to a new genus, Amarinus, in 1980. The name is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
meaning "not the sea", while the specific epithet means "of lakes".