Skin -The Wonderwrap-14

While taking a look at the outermost organ of "our beautiful bodies"-the skin, we have covered considerable ground. Now we are nearly on the last leg of this journey. We shall cover the annelida, the earthworm like creatures, nematoda - the roundworm and its kind, platyhelminthes - the flatworms, the coelenterates - the jellyfish and hydra like animals and finally the sponges, phylum porifera. But that will not be all, as the plants and even fungi have skins and they have many features similar to those of ours. In fact,all life is one, can be clearly realized as one gets more familiar with many different forms of life.

The group of animals called phylum annelida is represented by earthworm, leeches and many other animals less well known to a common man. Their bodies are made up of segments and the body is covered by acellular cuticle. Epidermal epithelium secretes the cuticle. The cuticle is albuminous and protective. It allows respiratory gases like oxygen and carbon-di-oxide move through freely. Not the leeches but other annelids have long hair-like projections sticking out of their skin. These are the setae. They help in locomotion and in getting a grip on the soil surface.

The setae come from a setigerous sac in earthworm's skin like our hair from a hair follicle. There hardly are any distinct muscles in annelidan skin. They have muscle fiber sheets in their dermis. Lack of distinct muscles makes it difficult for them to make precise movements.

One more special feature of annelida is - their skin contains mucus glands which produce large amount of mucus. The mucus is very useful in not allowing microbes to penetrate the skin, as also in lining the burrows of earthworms. The tunnels earthworms make, last longer as the mucus lining hardens on drying up. As you know earthworms are the "nature's ploughs" and aeration of soil can take place due to the tunnels which at times may be 5 feet deep. The mucus holds a film of water and thus prevents desiccation of the animals to some extent.

The skin of annelida is a sense organ too. It can sense touch, pressure, light, warmth and cold and vibrations with the sensitive cells in the skin. Nematodes - the round worm, thread worm, pin worm, guinea worm etc live as parasites in the bodies of their host. Their skin has a thick cuticle, which is all the time regenerated. If this armor were not there, they would be digested by the hostile environment inside the host's body.

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