Phylum Arthropoda - Classification of Multicellular Animals

Earlier you known how the coelom evolved and the body of the coelomates got segmented leading to evolution of segmentation or metamerism. The benefits of serial metamerism to animals were as well made clear to you. You have also seen how this feature was made use of by annelids to their maximum benefit, enabling them to occupy various niches, primarily aquatic, successfully. We now start the study of the largest phylum in the animal kingdom, phylum Arthropods. This phylum involves more than 1,000,000 species of animals that have been so far described. This number constitutes much more than three times the number of all the other species of animals which are known to exist in the biosphere. Arthropods having inhabited all types of aquatic habitats are the first chief group of animals to have invaded effectively the terrestrial environment occupying every possible niche there. Like annelids, arthropods are coelomates and segmented, and possibly both the phyla arose from a common ancestor.