Anespides.net

Anaspides

Why the Name?

 

 

Anaspides in the Family name for a small shrimp called Anaspides tasmaniae which is found only in Tasmania, Australia.

I wanted to find a website name that was distinctly Australian, had links to the southern hemisphere, and had something to do with earth science.  The name seemed appropriate.

Anaspides tasmaniae is a member of the Crustacean family and is a small freshwater mountain shrimp which essentially has remained unchanged for 250 million years (Triassic Period); it is a living fossil.

Anaspides tasmaniae - FACT SHEET

CLASS: Crustacea

SUBCLASS: Syncarida

ORDER: Anaspidacea

STATUS:  Endemic to Tasmania, Australia

Evolution and Systematics

The order Anaspidacea contains four families that have sometimes been divided into two suborders, the Anaspidinea and Stygocaridinea. The family Anaspididae has been known since the Triassic and exhibits strong relationships to the extinct order Palaeocaridacea. Anaspidaceans are generally thought to be among the most primitive of eumalacostracan crustaceans (that is, members of the subclass Eumalacostraca), especially because their thoracic limbs possess both epipods and exopods. However, details of their circulatory system, foregut morphology, and other aspects of their internal anatomy suggest that anaspidaceans are derived from ancestors leading to the eucaridan decapods. The lack of a carapace has caused debate about their exact placement among eumalacostracan crustaceans, but anaspidaceans are generally thought to be ancestral to at least the line leading to decapods, if not some of the other eumalacostracan groups as well.

Physical Characteristics

The anaspidacean head does not bear a carapace. Eyes may be on stalks, sessile on the head, or absent altogether. The first thoracic somite is fused to the head while the remaining seven thoracic somites are free. The first thoracic appendage is modified as a maxilliped, that is, it has a different morphology from the remaining seven pairs of thoracic limbs, and is modified as a feeding structure. Thoracic limbs two through eight have the endopod developed into full walking legs. On these appendages, the epipods, which emanate from the outside margin of the coxa, function as flattened gills, and the exopods, which come from the basis, function for water movement. Sometimes the exopods are not present. The pleopods may be strongly developed, reduced, or absent. In the Anaspididae, the telson and uropods form a tail fan, but in other families, the uropods are elongate and the telson short. Anaspidaceans can be up to 1.9 in (5 cm) in length, but some species are less than 0.39 in (1 cm). Colour is usually a dull brown.

Distribution

Anaspidaceans show a classic Gondwana relict distribution pattern, being found only in Tasmania, southeastern Australia, New Zealand, and southern South America. The family Anaspididae (of which there is only one species) are known only from a small number of localities in Tasmania and Victoria, Australia, while the Stygocarididae are more widely dispersed with species known from Victoria, Australia, New Zealand, Chile, and Argentina.

The first published record of Anaspides tasmaniae was made in 1893 from alpine pools on Mt. Wellington behind Hobart. Since then, it has been widely found on the Central Plateau, as well as in western and southern highland areas.

Habitat

The larger anaspidaceans are generally found in cool mountain streams, lakes, and swamps, while the smaller stygocaridineans are dwellers of the groundwater, living among the sand grains. The swamp-dwelling anaspidaceans live in the burrows of freshwater crayfish, while those found in lakes tend to live in the algal macrophyte mats on the lake bottom, and the stream-dwellers patrol over and among larger rocks of the streambed.

Anaspides tasmaniae typically is found in highland creeks and pools above 750 m in altitude. It has also been found in the underground waters of cave systems.

Behaviour

Anaspidaceans are not good swimmers. Instead, they spend most of their time walking over the substrate. The exopods of the thoracic legs are in nearly constant motion, most likely circulating fresh oxygen-bearing water past the flap-like epipods. When walking, the legs move in a metachronal pattern, which continues to the pleopods. In fact, in the larger species, the pleopods have the same motion as the walking legs, so that at first glance the animal looks to have a continuous set of legs all the way to the posterior end of the body. When startled, anaspidaceans are capable of an upward jump in which the body is flexed about midway along the back. On relaxation, the animal settles to the bottom and walks about as if nothing had happened. There appears to be no territoriality in anaspidaceans. When two individuals meet, they may touch antennae, but as often as not, one merely walks over the body of the other. Anaspides may be seen crawling across the bottom of a pool or stream, or else swimming near the water surface. It is a very shy creature, however, and when disturbed will dart into shelter with a sharp flick of its tail.

Feeding Ecology and Diet

Anaspidaceans are generalist feeders, eating organic detritus obtained from the substratum. The larger species may also be scavengers and appear capable of scraping organic films from the surfaces of small pebbles. They fees on submerged plant material such as algae and mosses. They may also prey on other aquatic animals such as tadpoles and worms. Anaspides has been observed preying on small insects that have fallen onto the surface of the water. To capture its prey the shrimp rolls onto its back.

Reproductive Biology

Mating has so far not been observed in this group. Egg laying occurs mostly in spring. The 1mm diameter eggs are attached to submerged plant debris or stones. There is no material caring for the eggs or the juveniles. Eight months or more later, the eggs hatch when the young are 2 to 3mm long. The longer developmental periods are associated with an over-wintering dormancy period. They will breed about 15 months later when approximately 18mm in length. Individuals may live for 3 or 4 years.

Conservation Status

Anaspidaceans are restricted in their distribution, but for the most part occur in areas where landscape development is minimal. As with many Gondwanan freshwater crustaceans, however, the introduction of trout into the rivers and streams by European colonizers has meant that some species survive only in the small tributaries where fishes cannot go. These crustaceans evolved in the absence of freshwater fishes, so they have no natural defences against those introduced predators. At present, none of the anaspidaceans are considered to be threatened, and none are listed by the IUCN.

Significance to Humans

Anaspidaceans represent an interesting evolutionary branch of crustaceans, and as such, are important in telling the history of life on Earth.

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