Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Branchiopoda
Order:
NotostracaG. O. Sars, 1867
Family:
TriopsidaeKeilhack, 1909
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] The members of the extinct order Kazacharthra are closely related, having been descended from notostracans.
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 Other common types are Triops numidicus from Africa, although it has been said that some papers refer to this as an outdated name for Triops granarius, which is from South Africa, China, Japan and Italy [2].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 elsewhere in Europe, for example in Britain where it is endangered, occurring only in pools in two localities, one being in England at New Forest the other in Scotland at Wildfowl & Wetlands Trust Caerlaverlock, which is near Dumfries.
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 Other common types are Triops numidicus from Africa, although it has been said that some papers refer to this as an outdated name for Triops granarius, which is from South Africa, China, Japan and Italy [2].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 elsewhere in Europe, for example in Britain where it is endangered, occurring only in pools in two localities, one being in England at New Forest the other in Scotland at Wildfowl & Wetlands Trust Caerlaverlock, which is near Dumfries.
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.
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.
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