Triops longicaudatus

Appearance

The heart of tadpole shrimps is a long dorsal tube in the anterior eleven trunk segments. It has a pair of ostia in each of these segments. Sometimes hemoglobin is present in its blood and the crustacean may be pink as a result. The excretory organs are the paired maxillary glands, located on the segment of the second maxilla. The long looped ducts of these glands can be seen in the carapace. The role of the maxillary glands is primarily osmoregulatory. Nitrogen, in the form of ammonia, is lost by diffusion across the gill surfaces.

Distribution

"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, the West Indies, and the Pacific Islands, including Japan and New Caledonia. The related European species "Triops cancriformis" is an endangered species in the United Kingdom, and is legally protected under Schedule 5 of the Wildlife and Countryside Act 1981.

Behavior

The feeding method of tadpole shrimps is similar to that proposed for the ancestral crustacean. The anterior appendages stir sediments and swirl muddy water into the wide, midventral food groove. The "gnathobases" guide food anteriorly to the mouth. The large flat exopods stir and lift the sediments. Fine silt particles and water escape easily, but large, coarse food particles are torn into smaller pieces by the blade-like, inward-facing lobes called "endopods" at the end of the leg.To complete their lives, tadpole shrimps depend on the changing nature of the temporary waters they inhabit. During the dry season, 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 is orange in color. It has a single eye, six legs, and develops through instars. 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.

Habitat

"T. longicaudatus" is the most widespread notostracan species, and may be found in western North America, South America, Japan, and several Pacific Islands. It is most active at a temperature of approximately 20 °C, 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 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.

Reproduction

"Triops" "longicaudatus" displays several reproductive strategies. Individuals may reproduce sexually, but this is rare, as most populations are highly male- or female-biased. Parthenogenesis 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.

Food

The feeding method of tadpole shrimps is similar to that proposed for the ancestral crustacean. The anterior appendages stir sediments and swirl muddy water into the wide, midventral food groove. The "gnathobases" guide food anteriorly to the mouth. The large flat exopods stir and lift the sediments. Fine silt particles and water escape easily, but large, coarse food particles are torn into smaller pieces by the blade-like, inward-facing lobes called "endopods" at the end of the leg.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. In turn, "Triops longicaudatus" are eaten by frogs and birds.