Titlebook: Animal Life in Fresh Water; A Guide to Fresh-Wat Helen Mellanby Book 1963 Helen Mellanby 1963 evolution.invertebrates.physiology.Model inve

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Ecosystem Engineers, Keystone Species,anus. A curious feature of the Nematodes is that the tissues of which their bodies are composed are made up of very few large cells; there are no cilia anywhere, no blood system, and no breathing organs. The eggs are covered by a hard shell. The young Nematode hatches looking very much like an adult

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Patrick M. A. James,Marie-Josée Fortin(.) on their bodies which are arranged in groups on each segment; they are used to obtain a hold on the sides of burrows, and they are a very valuable means of identifying a specimen. Worms all have distinct heads and tails though it is sometimes difficult to see which is which, but the mouth is ove

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Heinrich Walter,Siegmar-W. Brecklee the limbs used for locomotion (i.e. walking or swimming). The skin on the surface of the animals contains a particular substance called chitin and is waterproof. Frequently most of the skin tends to be rather hard and brittle, and movement would be difficult were it not that between the segments o

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Heinrich Walter,Siegmar-W. Breckleciliated, and the cilia make currents which collect the small organisms used as food, and transport them to the mouth. Polyzoa possess a proper gut, which terminates in an anus; ovaries and testes (they are hermaphrodites); and a rudimentary nervous system. The fresh-water polyzoa reproduce asexuall

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The True Worms (,),(.) on their bodies which are arranged in groups on each segment; they are used to obtain a hold on the sides of burrows, and they are a very valuable means of identifying a specimen. Worms all have distinct heads and tails though it is sometimes difficult to see which is which, but the mouth is ove

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