What is a phylum example and definition?

What is a phylum in biology?

A phylum is a taxonomic rank below kingdom, above class.

Members of a phylum are related to each other and to the kingdom, but less closely.

There is no formal definition of a phylum in biology, but it can be described as the largest group of organisms that are more closely related than members of the next lower taxon. It is not the longest defined taxon, however, because there are phylum-level taxa that are longer-lived than others: For example, bacteria, Archaea, Protista, Fungi, and Viridiplantae are all phyla on the cellular level, with some organisms on all five taxa having a longer lineage than others.

The first known use of the word "phylum" in an English context is from 1682. After Aristotle, the oldest mention of the term is from the Greek physician and naturalist Alexander von Humboldt. The phylum of animals is now called Animalia and is split into several subphyla (Animalia, Chordata, Arthropoda, Nematoda, Echinodermata, Chordata, Cephalorhiza, Cephalochordata, Gnathostomata, Lophotrochozoa, Mollusca, Nautiloidea, Onychoteuthidae).

For much of human history, taxonomy was organized by the Linnean system developed by Carl Linnaeus. This system is based upon a hierarchy of species. Species are grouped into genera, genera into families, families into orders, orders into classes, and classes into phyla. The phylum name has fallen out of use, largely because there are so many phylum names on the tree of life that Linnean names do not lend themselves to easy identification or use.

Some older names are familiar, such as Animalia. However, the earliest phylum name is Protozoa. Other early names were Spongia and for a time it was widely thought that the phylum Protozoa was related to Trichomonas.

Protozoa is Latin for "first", and refers to those cells of the earliest developing organisms that lack cell nuclei.