Notostraca

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Notostraca
Triops longicaudatus
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Subphylum: Crustacea Class: Branchiopoda Order: Notostraca G. O. Sars, 1867 Family: Triopsidae Keilhack, 1909
Genera
Lepidurus Triops

Members of 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]

Contents 1 Ecology 2 Distribution 3 Etymology of the word "Triops" 4 Classification 4.1 Notostracans in the aquarium 5 External links 6 References

[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, small, dying or weak tadpoles, and even each other. 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, their embryos remain in a state of diapause (suspended animation) and can survive for several years until the next rains fill up the pools again, allowing them to hatch.

Triops are often the top predators in vernal pools, as 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 by uprooting them while searching for food.

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] Etymology of the word "Triops"

"Triops" is a loanword from Greek, meaning "three eyes." Notostracans, indeed, have three eyes, in that, unlike in the related Fairy shrimps, the naupliar ocellus (the eye of the nauplis) is retained in the adult form, even as the two compound eyes develop. The two compound eyes look out for food and predators, but they can only see clearly for a short distance. The naupliar ocellus senses light, acting as an internal "compass".(In their natural habitat, the sun shines from above, therefore the animals believe that light is where "up" is.). Both the singular and plural is Triops. ^[3]

[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 lemmoni Holmes, 1894
• Lepidurus lynchi
• Lepidurus mongolicus Vekhoff, 1992
• Lepidurus packardii

Genus Triops Schrank, 1803

• 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, primarily Triops longicaudatus, 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. 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 they reach their maximum size of approximately 2 inches, including their caudal appendages. If food is not available in plenty--and sometimes even if it is--they 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.

By thoroughly drying the tank in which they are kept after a die-off and then allowing the completely dry tank to sit for at least a month and finally reflooding it with distilled or spring water, another generation of pets is easily generated, as the previous brood will have left eggs in the substrate. This simulates the periodic drying and flooding of the natural habitat of the tadpole shrimp.

[edit] External links

• MyTriops.com
• ARKive - images and movies of the tadpole shrimp (Triops cancriformis)
• / TRIOPS LIFE SCIENCE KITS
• / SEA-MONKEYS Science kit
• / Triops Photos
• / "Triops Tale" Science Fair Project

[edit] References

1. ^ 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.
2. ^ Species descriptions (2001). Retrieved on July 31, 2006.
3. ^ [1]