Triops
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The genus Triops belongs within the class of the gill pods (Branchiopoda) to the order of the back shell (Notostraca; also "paws" or "tortoiseshell"). Together with the genus Lepidurus , it is part of the Triopsidae, the only family within the back shell. The "primeval crab" Triops ( Greek : "the three-eyed") is a living fossil . Triops cancriformis is considered to be the oldest known living animal species in the world, which has been identified as a subspecies Triops cancriformis minor (†) in the 220 million year old Franconian Keuper ( Upper Triassic ). Morphologically largely unchanged, Triops cancriformis has survived in various subspecies to the present.
nomenclature
The name originally introduced for the genus by Franz von Paula Kasten , which became a protonym through the change , was Apus . The genus name was brought into the current form at the suggestion of AR Longhurst in 1955 in order to correct a homonymy with the bird genus from the family of sailors (Apodidae), which is inadmissible according to the rules of the ICZN .
Way of life
Two species have been more scientifically researched, so more is known about them. They are also the geographically most widespread representatives of the genus:
- Triops longicaudatus (focus of distribution in North and South America)
- Triops cancriformis (focus of distribution in Europe)
Both types are often offered in the trade in the form of their " permanent eggs ".
Unlike the custom of extremely salty water brine shrimp , the representatives of the genus are Triops exclusively in freshwater before. They are inhabitants of extreme biotopes : bodies of water that exist only for a very short time (astatic or temporary) that can form in suitable depressions , for example after heavy rainfall or seasonal floods. Their biology is adapted to the extreme dynamics of this habitat.
Reproduction
Upon reaching sexual maturity, Triops begins to lay down "permanent eggs" (actually encysted embryos in the gastrula stage ), which can sometimes rest in the ground for decades before the larvae ( nauplii ) hatch when they are flooded again . These exceptionally resilient cysts are a key adaption that enables them to survive what may be a long period of non-existence in their habitat. With Triops cancriformis , the survival of 27 years of drought has been proven in the field.
The nauplii usually hatch within 48 hours and develop into sexually mature animals in numerous moltings in seven to fourteen days. The speed of development depends on various ecological factors, but is largely determined by temperature and the food supply. Triops cancriformis reaches an average length of six to eight centimeters, the largest specimens caught so far eleven centimeters. The maximum lifespan is around twelve weeks outdoors. This short lifetime correlates with the short duration of their habitats .
Another adaptation is their variable reproduction strategy within a species. Asexual as well as sexual reproduction occurs - with different degrees of distinction in the different species. It has not yet been possible to confirm whether, as has often been suspected, parthenogenesis (virgin generation) is present. Self-fertilization (autogamy) by means of a hermaphrodite has been proven to take place, in this case the animals that appear outwardly as females are hermaphrodites ( hermaphrodites ). There are also bisexual relationships, whereby the gender relationship can vary between a slight excess of males up to populations in which males are a rarity (only about 1% of the population). The tiny permanent eggs can theoretically be easily spread by the wind and animals. It is not yet known to what extent the colonization of new waters actually takes place as a result.
