
''Lepidurus apus'', commonly known as a tadpole shrimp, is a
notostraca
The order Notostraca, containing the single family Triopsidae, is a group of crustaceans known as tadpole shrimp or shield shrimp. The two genera, ''Triops'' and ''Lepidurus'', are considered living fossils, with similar forms having existed since ...
n in the family
Triopsidae, one of a lineage of shrimp-like
crustacean
Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s that have had a similar form since the
Triassic
The Triassic ( ; sometimes symbolized š) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
period and are considered
living fossil
A living fossil is a Deprecation, deprecated term for an extant taxon that phenotypically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of or ...
s. This species is
cosmopolitan
Cosmopolitan may refer to:
Internationalism
* World citizen, one who eschews traditional geopolitical divisions derived from national citizenship
* Cosmopolitanism, the idea that all of humanity belongs to a single moral community
* Cosmopolitan ...
, inhabiting temporary freshwater ponds over much of the world, and the most widespread of the tadpole shrimps. Like other notostracans, ''L. apus'' has a broad
carapace
A carapace is a dorsal (upper) 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 unde ...
, long segmented
abdomen
The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...
, and large numbers of paddle-like legs. It reproduces by a mixture of sexual reproduction and self-fertilisation of females.
Description
''Lepidurus apus'' grows to in length. Its long abdomen is divided into about 30 segment-like rings, with two long caudal rami or "tails" attached behind the last ring.
Between the tails is a projection which distinguishes ''
Lepidurus
''Lepidurus'' is a genus of small crustaceans in the order Notostraca (tadpole shrimp). It is the larger of the two extant genera of the tadpole shrimps, the other being ''Triops''. They are commonly found in vernal pools and survive dry periods ...
'' from ''
Triops
''Triops'', from Ancient Greek ĻĻία (''trĆa''), meaning "three", and į½Ļ (''óps''), meaning "face" or "eye", is a genus of small crustaceans in the order Notostraca (tadpole shrimp). The long-lasting resting eggs of several species of '' ...
'', the other notostracan
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
. Its carapace is flat with an average length of , and is attached only at the front, covering up to two thirds of the abdomen. The carapace is a mottled dark yellow/brown colour transitioning to a lighter edge, and bears a single pair of compound eyes.
At the front of the abdomen are one or more (up to three) pairs of feelers. Under the body are 41ā46 (average 44) pairs of paddle-like limbs used for swimming.

Males are readily identifiable by the lack of ovisacs, and also have subtle differences in the carapace. Females and hermaphrodites look virtually identical, but hermaphrodites have testicular lobes amongst their ovarian lobes, which allows them to reproduce in isolation.
''L. apus'' is often referred to as a āliving fossilā, virtually unchanged for over 300 million years. However, a recent study suggests that resemblance to fossil notostracans is probably a result of the "highly conserved general morphology in this group and of
homoplasy
Homoplasy, in biology and phylogenetics, is the term used to describe a feature that has been gained or lost independently in separate lineages over the course of evolution. This is different from homology, which is the term used to characterize ...
". Recent species of ''Lepidurus'' are morphologically nearly identical to fossil records but may "represent very different evolutionary lineages".
Distribution and habitat
Global range
''Lepidurus apus'' is perhaps the most cosmopolitan of all the Notostraca, occurring widely around the world including, but not limited to,
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmassesāthe North Island () and the South Island ()āand List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
,
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
,
Iran
Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
,
Israel
Israel, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...
,
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
,
Germany
Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
,
Italy
Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
,
Denmark
Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...
, and
Austria
Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...
. ''Lepidurus apus'' is split into several geographic subspecies, such as ''L. apus viridis,'' present in parts of Australia, Tasmania and New Zealand.
Habitat preferences
''Lepidurus apus'' is found predominantly in temporary freshwater ponds, 10ā100 cm deep, filled during autumn and winter, and drying out over spring and summer. It is less common in permanent water bodies such as swamps and ditches. ''Lepidurus apus viridis'', for example, is found throughout New Zealand in small ponds and ditches.
Its life-cycle allows it to become dormant if the pond freezes over, is covered with snow, or dries out; it can persist in the dry sediment margin as a
cyst
A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubb ...
form, which can survive harsh conditions for many years until the pond reappears.
''L. apus'' prefers a
pH between 6 and 7.8, and can tolerate relatively high concentrations of chemicals, such as levels of total
nitrate
Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
of 1 mg/L and
phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
of 0.1 mg/L, a level which would be detrimental to other aquatic species.
Wetlands and temporary ponds worldwide are increasingly being converted to grasslands for agriculture, so the total land area available for ''L. apus'' is gradually diminishing. Some subspecies may become threatened in future, or may already be under threat, although our knowledge is limited.
''L. apus'' is well-adapted to variations of climate and location, disperses easily, and has highly resilient eggs, so appears to be less sensitive to human pressures across its wide geographical range.
Life cycle
''Lepidurus apus'' has an unusual life-cycle: it is able to produce microscopic cysts that can lie dormant for years at a time through extreme conditions, letting it survive in areas with vastly different climates such as Morocco and Denmark. These "resting eggs" are so drought resistant there is a record of hatching after being kept dry for 28 years.
The species is hermaphroditic; no males are found in the New Zealand subspecies ''viridius'',
but in Italy there are males that are non-functional. Different subspecies of ''Lepidurus apus'' have different methods of fertilisation, some by a male, some by hermaphroditic individuals.
Cysts average 0.447 mm in diameter,
and have been found at concentrations of 250 per 100 cm
2.
They are laid on gravel in the middle of ditches or ponds, to avoid (it is speculated) large animals such as sheep transporting the cysts onto land.
The cysts can survive drought and sub-zero temperatures,
and can even synthesise haemoglobin if there is a lack of oxygen.
As the pond dries out in the summer, the cysts will lie dormant until immersed in water. Light is an important factor in hatching: experiments showed no cysts hatched in darkness, some hatched after 10 mins of bright light, and all hatched in continuous light.
They hatched between 10 °C and 24 °C, though the optimum was 16 °C and 20 °C, and even then hatch rates did not exceed 60%.
Hatching often happens after winter rainfall forms temporary ponds. Larvae feed and rapidly grow to maturity, in as little as 4 weeks in optimum conditions in the warmer summer and spring months.
''Lepidurus apus'' has been found globally in remote areas with no waterways to transport individuals. In dry conditions, the dust-like resting eggs are easily
distributed by wind. ''Lepidurus apus'' eggs are also thought to be distributed by water, people, wildlife, and migratory birds.
Diet
''Lepidurus apus'' is omnivorous, feeding on both plant matter, mostly floating detritus, and small aquatic invertebrates such as
fairy shrimp
Anostraca is one of the four orders of crustaceans in the class Branchiopoda; its members are referred to as fairy shrimp. They live in vernal pools and hypersaline lakes across the world, and they have even been found in deserts, ice-covered mou ...
and
water flea
The Diplostraca or Cladocera, commonly known as water fleas, is a superorder of small, mostly freshwater crustaceans, most of which feed on microscopic chunks of organic matter, though some forms are predatory.
Over 1000 species have been recog ...
s.
It swims along the bottom of ponds, stirring up the substrate as it forages. ''L. apus'', as with other species of ''Lepidurus'', also feeds upon algae, myxozoa, bacteria and fung''i.''
Predators and parasites
Predators of ''Lepidurus'' include small wading birds such as
sandpiper
Scolopacidae is a large family of shorebirds, or waders, which mainly includes many species known as sandpipers, but also others such as woodcocks, curlews and snipes. Most of these species eat small invertebrates picked out of the mud or so ...
s or
stint
A stint is one of several very small waders in the paraphyletic ''"Calidris"'' assemblage ā often separated in ''Erolia'' ā which in North America are known as peeps. They are Scolopacidae, scolopacid waders much similar in ecomor ...
, larger waterfowl like
duck
Duck is the common name for numerous species of waterfowl in the family (biology), family Anatidae. Ducks are generally smaller and shorter-necked than swans and goose, geese, which are members of the same family. Divided among several subfam ...
s and
swan
Swans are birds of the genus ''Cygnus'' within the family Anatidae. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe (biology) ...
s, and, in some ponds, fishes.
Migrating birds feed from temporary pools, as well as itinerant birds already found in the area. The rapid abundance of ''Lepidurus apus'' and other small invertebrates in pools often results in an increase in bird numbers in the area.
''Nosema lepiduri'' is a microsporidian parasite found in water bodies less than 15 cm deep that internally parasitises ''Lepidurus'' with spores, in some cases killing the host. Infected ''Lepidurus'' have a milky white colouration on the legs and carapace due to internal infection.
Conservation status
The subspecies ''Lepidurus apus viridis'' has been classified by the New Zealand
Department of Conservation
Department may refer to:
* Departmentalization, division of a larger organization into parts with specific responsibility
Government and military
*Department (administrative division), a geographical and administrative division within a country, ...
as Nationally Endangered under the
New Zealand Threat Classification System
The New Zealand Threat Classification System is used by the Department of Conservation to assess conservation priorities of species in New Zealand.
The system was developed because the IUCN Red List, a similar conservation status system, had s ...
.
References
External links
* The tadpole shrimp was discussed on RadioNZ ''Critter of the Week''
1 April 2016
{{Taxonbar, from=Q1317340
Notostraca
Taxa named by Carl Linnaeus
Cosmopolitan arthropods
Crustaceans described in 1758