Major and Minor Phyla
All the identified species of animals are divided into a number of phlya (singular: phylum). These phyla are further divided broadly into 2 broad categories: major phyla and minor phyla. The concept of major or minor phyla depends on 2 aspects:
- Number of species and individuals in that phylum.
- Participation in the ecological communities.
9 phyla are regarded as major phyla, viz, Protozoa, Porifera, Coelenterata, Platyhelminthes, Nematoda, Mollusca, Annelida, Arthropoda and Echinodermata. These phyla have large number of species and individuals as well as these are found in many ecological communities, playing an elaborate role in them.
Minor phyla have comparatively very lesser number of species and individuals as well as their participation in ecological communities is limited when compared to major phyla. The minor phyla include: Rotifera, Ectoprocta, Ctenophora, Hemichordata, Onychophora, Acanthocephala, Nemertinea, Pogonophora etc.
Although phyla Rotifera and Ectoprocta have large number of species, but are still not considered as major phyla because their role in ecological communities is quite limited. Therefore, rotifera and ectoprocta are minor phyla.
It is also important to note that this customary division of all phyla into minor and major phyla is applicable only to invertebrates. Therefore, no vertebrate can be found classified into minor phyla.