Triops longicaudatus (commonly called longtail tadpole shrimp, American tadpole shrimp, or rice tadpole shrimp) is a freshwater crustacean of the order Notostraca, resembling a miniature horseshoe crab. It is characterized by an elongated, segmented body, a flattened shield-like brownish carapace covering two thirds of the thorax, and two long filaments on the abdomen. Triops refers to its three eyes, and longicaudatus refers to the elongated tail structures. Triops longicaudatus is found in freshwater ponds and pools, often in places where few higher forms of life can exist. Like its relative Triops cancriformis, the longtail tadpole shrimp is considered a living fossil because its basic prehistoric morphology has changed little in the last 70 million years, exactly matching their ancient fossils. Triops longicaudatus is one of the oldest animal species still in existence.
Triops longicaudatus is a member of the crustacean class Branchiopoda, which primarily contains freshwater animals with gills on their legs. The class Branchiopoda is divided into the subclasses Sarsostraca, containing fairy shrimp, and Phyllopoda, containing all other members (cladocerans, clam shrimps, and the tadpole shrimp). The subclass name, literally meaning leaf-footed, is derived from their flat, leaflike appendages. Notostracans are placed in the infraclass Calamanostraca, which also contains the extinct Kazacharthra.
Triops longicaudatus displays several reproductive strategies. Individuals may reproduce sexually, but this is rare, as most populations are highly male- or female-biased. Parthenogenesis (development from unfertilized eggs) is the most common reproductive strategy. Some populations, however, consist of hermaphrodites who fertilize each other. Different populations display different strategies or combinations of strategies, and may therefore, be considered separate species or subspecies in the future.
In females, the eleventh pair of legs is modified into egg sacs, where the eggs are carried for several hours. The eggs are released in batches, have a thick shell, and can stand freezing temperatures as well as drought, enabling the population to survive from one season to the next. The eggs have to dry out completely before being submerged in water again in order to hatch successfully; they may remain in a state of diapause for up to 20 years. These eggs may have helped Triops longicaudatus, as well as other notostracans, to survive the various natural disasters and mass extinctions to date.
To complete their lives, tadpole shrimps depend on the changing nature of the temporary waters they inhabit. During the dry season (summer and fall), their offspring stay inside the eggs. As the pool fills with rainwater during the winter and spring, they hatch and feed on fairy shrimps and other invertebrates. The first larval stage (the metanauplius) is orange in color. It has a single eye, six legs, and develops through instars (growth stages). Each instar ends with shedding the exoskeleton. The number of segments and appendages increases as Triops grow, and they slowly change to greyish brown. In approximately eight days, they reach maturity and lay eggs. Adult Triops die as the pools dry up. Triops generally live for about 20–90 days if the pool does not dry up. Talk about a stressful situation, eh?
T. longicaudatus is the most widespread notostracan species, and may be found in western North America, South America, Japan, South Korea, and several Pacific Islands. It is most active at a temperature of approximately 20 °C (68 °F), and is usually found scratching the mud at the bottom of pools, searching for benthic food. Triops collect food particles by straining the water with hairs on their limbs. Loose food particles are collected in a groove running down the underside of the body lengthwise, and held together by a sticky secretion until they are swallowed by their very small (2 mm wide) mouth. The tiny mouth is deep in its underbelly, and while the animal is capable of breaking up plant roots or dead fish, it is incapable of chasing down and eating prey larger than it is.
Where Do They Come From?
Triops longicaudatus is widespread in North America. In Canada, it is found only in the provinces of Alberta, Saskatchewan and Manitoba. It is widespread throughout the contiguous United States, Mexico, and Hawaii, but not Alaska. Tadpole shrimps may be found in parts of South America, in (Argentina and Galápagos Islands), the West Indies, and the Pacific Islands, including Japan and New Caledonia.
Tadpole shrimps are omnivorous and may eat algae, insects, and other organic debris; they are known to chase very small fry, tadpoles, and oligochaete worms. In general, they eat anything organic that is smaller than they are, which even may include their siblings (they are cannibalistic). In turn, Triops longicaudatus are eaten by frogs and birds.
Interaction with Humans
The species is considered a human ally against the West Nile virus, as the individuals consume Culex mosquito larvae. They also are used as a biological agent in Japan, eating weeds in rice paddies. In Wyoming, the presence of Triops longicaudatus usually indicates a good chance of the hatching of spadefoot frogs.
Dried eggs of Triops longicaudatus are sold in kits to be raised as aquarium pets, sold under the name of “aquasaurs”, “trigons” or “triops”. These are most often of the greenish-brown variety, but the red variant is fairly common among enthusiasts. Captive Triops are frequently kept in aquariums and fed a diet consisting mainly of carrots, shrimp pellets and dried shrimp. Often they are also given living shrimp and daphnia as live prey. Because they can feed on just about anything, they are also fed lunch meat, potatoes, crackers, etc. They will often feed themselves by grazing on algae and other grunge from the bottom and sides of the tank and on small particles clinging to sponge filters or to Marimo moss balls, which are often cultured alongside Triops.
Did you know that triops are sold from many vendors all over? I have included a few links below for you to check out but don’t recommend any one in particular: