Notostraca
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 Triops longicaudatus
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The order Notostraca (colloquially referred to as notostracans, called Triops, tadpole shrimp or shield shrimp) are small crustaceans in the class Branchiopoda. Triops have two internal compound eyes and one naupliar eye in-between, a flattened carapace covering its head and leg-bearing segments of the body. The order contains a single family, with only two extant genera. Their external morphology has apparently not changed since the Triassic appearance of Triops cancriformis around 220 million years ago. Triops cancriformis may therefore be the "oldest living animal species on earth" [1].
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[edit] Ecology
Tadpole shrimps usually live near the ground of astatic pools, where they move with their ventral side down. However, lack of oxygen can force them to swim upside-down with their gill-like legs close under the surface of the water. Notostraca are omnivorous; they dig around in the mud using the frontal part of their shield, looking not only for plankton but also for larger prey such as worms, chironomid larvae and even weak tadpoles. Anostracans, often associated with notostracans, can also be a considerable part of their prey (especially when weak or dying).
Notostracans sometimes even cannibalise freshly moulted members of the same species. In northern and central Europe, with few exceptions, all tadpole shrimps are female, whereas the sexes in southern and western Europe as well as in northern Africa are nearly equal in number. These "females" possess hermaphroditic glands, but instead of selfing, parthenogenesis takes place. Modified appendages of the 11th pair of limbs bear the ovisacs with the mature eggs.
Triops survives in temporary pools all over the world, and are correspondingly short-lived. These ponds usually dry up during certain times of the year when there is no rainfall. Although the adult Triops die during these droughts, the embryos remain in a state of diapause (suspended animation) until the rains return and fill up the temporary pools once again, allowing them to hatch.
Triops are often the top predators in vernal pools, and they will eat anything smaller than themselves. They also are an important food source for visiting birds. In some areas, certain species of Triops are considered pests, as they damage young rice plants.
The maximum life spans in the lab agree with data from field observations on Triops survival. In the lab, T. longicaudatus has a maximum lifespan of about 50 days and T. cancriformis a maximum lifespan of about 90 days, with some individuals beginning to die off as soon as two weeks after hatching. Secondarily, some may suffer premature deaths from moulting complications or other reasons.
[edit] Distribution
Notostracans can be found on every continent except Antarctica.
In Austria, two notostracan species (one spring species and one summer species) are documented: Lepidurus apus and Triops cancriformis. In the Americas, several species have been identified, including Triops longicaudatus and Triops newberryi. In Australia, Triops australiensis is found. Other common types are Triops numidicus from Africa, although it has been said that some papers refer to this as an outdated name for Triops granarius, which is from South Africa, China, Japan and Italy [2]. Triops cancriformis is also found in Britain, but is endangered, occurring only in pools in two areas, one in England at New Forest and one in Scotland at Wildfowl & Wetlands Trust Caerlaverlock, which is near Dumfries.
[edit] Classification
Genus Lepidurus Leach, 1819
- Lepidurus apus (Linnaeus, 1758)
- Lepidurus arcticus (Pallas, 1776)
- Lepidurus batesoni Lonhorst, 1955
- Lepidurus bilobatus Packard, 1883
- Lepidurus couesii Packard, 1875
- Lepidurus cryptus Rogers, 2001
- Lepidurus lemmonii Holmes, 1894
- Lepidurus lynchi
- Lepidurus mongolicus Vekhoff, 1992
- Lepidurus packardii
- Triops australiensis (Spencer & Hall, 1895)
- Triops cancriformis (Bosc, 1801)
- Triops granarius Lucas, 1864
- Triops longicaudatus (LeConte, 1846)
- Triops numidicus
- Triops newberryi (LeConte, 1846)
[edit] Notostracans in the aquarium
Notostracans are often sold to children in small packets as eggs as an interesting science project or as a beginner's kit for their first aquarium. The species commonly supplied with these kits is Triops longicaudatus. One pours distilled or spring water onto the eggs, and they will hatch out very quickly--often within less than a day. They will also grow at a remarkable pace; growth is actually noticeable from one day to the next until Triops longicaudatus' maximum size is reached at approximately 2 inches, including their caudal appendages. If food is not available in plenty--and sometimes even if it is--Triops longicaudatus will not hesitate to eat each other.
These creatures can make a useful addition to a freshwater aquarium, as they keep the substrate very clean and eat almost anything they find. They may, however pose a slight danger to very small fish or other crustaceans, and may in turn be eaten by large fish. Also, they may damage the roots of aquarium plants they encounter if not kept well fed. They are also very short-lived pets, but are easily replaceable.
[edit] External links
- MyTriops.com
- ARKive - images and movies of the tadpole shrimp (a Lepidurus species and Triops cancriformis)
[edit] References
- ^ Kelber, K.-P. (1999). Triops cancriformis (Crustacea, Notostraca): Ein bemerkenswertes Fossil aus der Trias Mitteleuropas. — In: Hauschke, N. & Wilde, V. (eds.): Trias - Eine ganz andere Welt, III.16: 383-394. Verl. Dr. F. Pfeil, Munich.
- ^ Species descriptions (2001). Retrieved on 2006-07-31.
