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The Robinson Library >> Science >> Zoology >> Crustaceans >> Sub-Class Branchiopoda

Triops cancriformis; an extremely ancient species



The main body of apus is 1-2 inches long and is colored brownish or olive-green. It has many pairs of limbs when fully grown, each ending in several filaments, and at is rear end is a pair of long whip-like appendages (known as furcae). In addition to acting as rudders, the furcae probably function as posterior antennae, giving warning of any attack from the rear. There are two compund eyes set closetogether near the leading edge of the carapace, and another single eye on the underside.

Apus swims on its back, by means of an almost nonstop wavelike motion of its many limbs and their filaments. This action probably also helps in respiration, by creating currents that wash over the gills, so increasint the amount of oxygen taken in.

Distribution and Habitat

Apus is widely distributed in Europe through to Russia, and from the Middle East to India, but can only live and breed satisfactorily in warm conditions. It generally lives in temporary pools where there are no fish or other predators.


Apus feeds on algae and other small organims such as insect larvae that it finds by grubbing in the mud at the bottom of the pond or pool in which it lives. It also gets some food from the water itself, using its waving limbs to collect and transfer food particles to the mouth. Apus will also eat larger animals and even dead or dying of its own kind. Such food is shredded by tough chitinous teeth located at the bases of the trunk limbs, as well as by mandibles.


It appears that the vast majority of apus are self-fertile hermaphrodites, but sexual reproduction does occur among some populations in warmer climates.

Due to the uncertain nature of the ponds in which apus lives, it has an extremely fast life cycle, developing from an egg to an adult in just two or three weeks. At each stage of development, a new body segment appears, the limbs become more numerous, and the forked tail filaments increase in length. When fully grown, the trunk consists of 33 segments, each of them, except the last five, bearing up to five pairs of limbs.

The adults die when the pond dries out, but the eggs can remain dormant for decades before hatching when the pond is re-flooded.

It is not known how the eggs of apus are spread.

Other Information

It is possible (if not likely) that both apus and horsehoe crabs share an ancestry via the ancient trilobites.

A true living fossil, apus has remained virtually unchanged as a species for 180 million years.

Scientific Classification

phylum Arthropoda
class Crustacea
sub-class Branchiopoda
order Notostraca
genus & species Triops cancriformis

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The Robinson Library >> Science >> Zoology >> Crustaceans >> Sub-Class Branchiopoda

This page was last updated on March 24, 2018.