Triops longicaudatus
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| Triops longicaudatus (LeConte, 1846) |
Triops longicaudatus (common names include American tadpole shrimp and longtail tadpole shrimp[1]) is a primitive freshwater crustacean in the order Notostraca. This is the best known tadpole shrimp species, for it is studied more than any other[2]. Triops longicaudatus is well suited for the ephemeral pools it inhabits, which are filled with water in the spring, but completely dry out in the hot months[3]. Its close relative, Triops cancriformis, first appeared during the Triassic, approximately 220 million years ago, and is presumably the oldest living animal species on the planet[4]. T.longicaudatus appeared later, just before the first dinosaurs, and is also considered a living fossil. These crustaceans therefore became very popular in North America — they are often sold as dried eggs in special raising kits. They are mainly found in Southwestern North America, throughout South America Japan and several Pacific Islands.
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[edit] Structure
All notostracans have two compound eyes and a naupliar ocellus in between them. A flat, shieldlike carapace covers the anterior segments. Apparently, this morphology has not changed since the first appearance of T. longicaudatus, which is the reason paleontologists tend to classify the fossils and today's living individuals as. The six walking legs are generally biramous, covered with leaf-like external gills (giving rise to their subclass name, Phyllopoda - meaning "leaf leg") and fine reddish hairs. The head and thorax are not fused to form a cephalothorax; the boundary can be seen on the carapace in the form of two grooves just behind the eyes. The first pair of antennae is highly reduced and is not visible dorsally, while the second pair is long, thin and triramous (branching into three parts). Crushing mandibles and the first leglike maxilla is present, but not the second maxilla. The gills are not hidden inside the carapace. There is a small lobe on the first leg, which is thought to be a reduced pincer.
The body is up to 8 cm long, including the uropods. Triops have up to 80 legs, all on the thorax. In contrast, the abdomen is fused with the telson and therefore consists of a single segment, bearing a pair of whiplike uropods. The uropods are often nearly as long as the rest of the body, which gives rise to the common name longtail tadpole shrimp.
Although the nauplii are tiny (sometimes less than 1 mm), they can reach a few centimetres in one week. A human equivalent would mean a baby growing into a 13-metre giant by the end of that first week. Notostracans are among the largest of all branchiopods.
[edit] Reproduction and development
Most individuals of Triops longicaudatus are either male or female. Like most other notostracans, however, they mainly reproduce asexually; a partner is often difficult to find as about most Triops are female. In fact, notostracan populations have been found where there was one male per 100 females. A few populations are composed entirely of females. Most females therefore possess hermaphroditic glands.However, they are capable of mating, if a male is available. Eggs are carried inside the eleventh pair of thoracic appendages, which are modified to form ovisacs. Because they live in temporary pools, Triops are correspondingly short-lived; the record for the species is 90 days, while the order record is 100 days, set by Triops cancriformis.
[edit] Ecology
Triops are omnivores, and like a variety of foods: plankton, worms, mosquito larvae, small plants, weak tadpoles, vegetables, and special fried fish pellets (the latter two are usually received in captivity). The larvae may even cannibalize their smaller siblings. These crustaceans strain food from the water with their hairy legs, and it is guided to the mouth by currents made by moving legs. If there is a drought, adult notostracans die, but their eggs enter a state of diapause - they stop developing for a period of time. When they are in water again, the eggs continue their development, and new larvae are hatched[5]. Triops may have economic significance as a form of mosquito control.
[edit] Subspecies
No subspecies of T. longicaudatus have yet been described, but genetic data suggests there are at least a few of them, if not dozens. However, two distinct varieties can be identified: "long-tailed" and "short-tailed", which can be distinguished by counting the segments not covered by the carapace. They may be classified as Triops longicaudatus longicaudatus and T. l. intermedius.
[edit] Gallery
 Triops longicaudatus in aquarium |
 Adult 2.5 cm Triops in aquarium |
 Magnified leg |
 Magnified head: 1 - ventral groove; 2 - mouth; 3 - mandible |
[edit] References
- ^ Grzimek's Animal Life Encyclopedia, 2nd Ed., (2004). Volume 02 - Protostomes
- ^ http://mytriops.com/
- ^ Triops longicaudatus. German Wikipedia (2007-03-06).
- ^ Notostraca
- ^ Encarta Reference Library 2005
