Do you know how does peripatus link the worms and the animals with jointed legs? This insignificant looking creature excited zoologists in the nineteenth century when it was first discovered because it was unlike any other animal is known at that time. It looks very much like a worm and yet it has rows of stumpy legs on either side and shows other features similar to animals of the phylum Arthropoda (animals with jointed legs).
The arthropods are the biggest and most diverse group of invertebrates and have successfully colonized the land and learned how to fly. They include the crustaceans (barnacles, shrimps, lobsters, and crabs), centipedes and millipedes, arachnids (spiders, scorpions, ticks, and mites) and the in seats.
The feature that has been most responsible for the success of the arthropods in their tough external covering called an exoskeleton. This supports the animal’s soft body on land and at the same time prevents it from losing water by evaporation. It is light enough to allow easy movement and yet also provides good protection.
Because periapts have features which are both worm-like (thin skin, eyes), and arthropod-like (claws, breathing system), it is thought to be descended almost unchanged from the animals that gave rise millions of years ago to the worms and arthropods.
Are water fleas really fleas?
True fleas are parasitic insects. Water fleas are so called because of their erratic, flea-like swimming movements. The water fleas are common freshwater crustaceans and they are fascinating to watch in a pond or better still in an aquarium.
The folded a shell which encloses the body is transparent and through it, you can easily watch the workings of the water flea’s body. The heart can be seen pumping away, and several pairs of feet are visible beating the water, filtering out single-celled algae and bacteria for food.
You can even see the eggs and develop young on the back of the females. Watch how the water flea sinks a little and then frantically jerks its way back to its original position by thrashing the water with its two pairs of branched antennae.
What are copepods?
Copepods are another group of small crustaceans which live in the sea. They are better swimmers than the freshwater water fleas and use their legs as well as their antennae to propel themselves through the water. Copepods drift in enormous numbers in the upper levels of the sea.
Together with other minute creatures, they form plankton on which all other higher animals feed, either directly or indirectly. Thus they are a very important link in the food chain that ends with the man himself.
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