Phylum (redirected from phyla)

phylum, in taxonomy: see classification.

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phylum

a major taxonomic division of living organisms that contain one or more classes. An example is the phylum Arthropoda (insects, crustaceans, arachnids, etc., and myriapods)

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phylum [′fī·ləm]

(systematics)

A major taxonomic category in classifying animals (and plants in some systems), composed of groups of related classes.

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Phylum 

(also type), the highest taxonomic category in the classification of animals. A phylum, or type, is made up of related classes. The term “type” was proposed in 1825 by H. de Blain-ville, who applied it to the four “branches” of animals distinguished by G. Cuvier in 1812.

Phyla vary in size: for example, the phylum Porifera comprises approximately 5,000 species, whereas the phylum Pogonophora has only about 100 species. Phyla are frequently divided into sub-phyla. For example, the phylum Chordata has four sub-phyla—Cephalochordata, Tunicata, Acrania, and Vertebrata. Organisms belonging to the same phylum are marked by the same structural organization. The number of phyla and their size vary from one classification system to another. Some taxonomists recognize as few as ten phyla, and others as many as 33. However, these differences do not diminish the importance of phyla as categories that reflect the principal branches of the phylogenetic tree of the animal kingdom.

In plant classification, which has been worked out independently from animal classification, the taxonomic category corresponding to a phylum is called a division.

M. E. KIRPICHNIKOV