In animals, the body cavity between the alimentary canal and the body wall is covered by a membrane called peritoneum and filled with chyloemic juice. It arises from embryonic mesoderm. According to the nature of Siloam, animals can be divided into 4 categories.
(i) Acoelomate: Animals that do not have a coelom are called acoelomates. Their spaces are filled by spongy parenchyma cells. Animals of the order Porifera, Platyhelminthes, Cnidaria and Ctenophora are asilomates. For example – Tapeworm (Taenia solium), Hydra (Hydra viridis), Liverworm (Fasciola hepatica) etc.
(ii) Pseudocoelomate: The body cavity between alimentary canal and body wall is not covered by peritoneum in animals called pseudocoelomate. Animals of the order Nematoda, Rotifera, Acanthocephola, Ectoprocta and Kinorhyncha are pseudocylomates. Such as round worm (Ascaris lumbricoides), eye worm (Loa loa), hook worm (Ancylostoma duodenale) etc.
(iii) Coelomate: The body cavity between alimentary canal and body wall is covered by peritoneum in animals called coelomate. Animals belonging to the order Annelida, Arthropoda, Echinodermata, Mollusca, Hemichordata and Chordata are coelomates. Such as earthworm (Metaphire posthuma), human (Homo sapiens), mosquito (Culex pipiens), sea star (Asterias vulgare), hilsa (Tenualosa ilisha), oyster (Unio marginalis) etc.
Silom is divided into two parts based on embryonic development.
(i) Psyzocilous chyloem: The chyloem that arises from embryonic mesodermal tissue is called zygosylous chyloem. For example Annelida, Arthropoda and Mollusca.
(ii) Enterocillus chyloem: The chyloem arising from the embryonic mesodermal sac is called enterocylus chyloem. For example, Echinodermata and Chordata.
Importance of coelom
(i) Cells help in independent growth and movement of various organs.
(ii) It protects the various parts of the animal body from friction.
(iii) Siloam helps transport waste materials, nutrients and gaseous materials.
(iv) It acts as a hydrostatic skeleton during locomotion of the animal.