Animal Diversity by Diana R. Kershaw (auth.) PDF

By Diana R. Kershaw (auth.)

ISBN-10: 041253200X

ISBN-13: 9780412532009

ISBN-10: 940116035X

ISBN-13: 9789401160353

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Phylum Porifera The simplest multicellular animals are the sponges, the phylum Porifera. ) comes from a member of this phylum, though by the time it reaches the bathroom the organism bears little resemblance to its natural state. In fact the bath sponge represents the supporting structure of the living organism. In life most sponges look rather unstructured, and appear in a variety of colours: green, yellow, red, purple, and orange being common. Because of their apparent lack of movement and their 'un-animal-like' coloration, sponges were regarded as plants by ancient naturalists such as Aristotle and Pliny.

Each individual is vase-shaped with a central cavity (the paragaster or spongocoele) and a large opening (the osculum) at the opposite end of the attachment (stolon). The sponge wall consists of three layers: an outer pinacoderm; a supporting gelatinous protein matrix, the mesohyal; and an inner feeding layer of choanocytes, which are closely similar to the choanoflagellates. The pinacocytes are highly contractile, and thus the animal is able to increase or decrease in size. Further contract ability is provided in some species by the collenocytes, which have long cytoplasmic strands extending across the spaces through The protozoan ciliates demonstrate the greatest complexity that has evolved in a unicellular organism.

Another example is seen in the suctorian Sphaerophyra, which lives inside the endoplasm of Stentor. Ecto- and endo- commensals are more common. Kerona is a crawling ciliate which lives on the surface of Hydra. Balantidium coli is endocommensal in pig intestines and transferred by means of cysts in the pig's faeces . Diplodinium ecaudatum is a highly elaborate ciliate which lives as a commensal in the rumen of cattle. In many ways it may be regarded as showing the greatest complexity achieved by a single cell.

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Animal Diversity by Diana R. Kershaw (auth.)

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Categories: Zoology