Connecting People with Nature


Essential Knowledge for Naturalists

The Animal Kingdom

With such an overwhelming array of animals in the world, it is difficult to imagine how to begin categorizing them. Luckily, Linneaus, back in the 18th century, gave us a good start. He devised the two-name system of Genus and species, which we still use today. Over time, scientists interested in the relationship of animal species to one another devised a number of other categories above the genus and species. There are generally seven steps in the hierarchical system. Genus and species are the lowest two groups. Each genus belongs to a family. Each family belongs to an order. Each order belongs to a class, and each class belongs to a phylum. Above the phylum is the kingdom.

The animal kingdom is broken down into perhaps 35 recognized Phyla. There are 5 however that contain most of the common species of terrestrial and freshwater systems. Of these, really the Chordates, the arthropods, and the molluscs are of primary interest, at least to the beginning naturalist.

Segmented Worms

The phylum annelida consists of the segmented worms: earthworms, leeches, and polychaetes. These wriggly creatures can be found just about anywhere on earth that meets their biological needs. There are perhaps 9,000 species of segmented worms on earth. Learn more about these creatures by visiting Berkeley's life history of Annelids, or segmented worms


The molluscs include clams, oysters, mussels, snails, octopus, squid, and similar life-forms. These mostly aquatic animals have a simple nervous system, and a fairly well developed digestive system, with some species of molluscs having a complete digestive tract basically similar to our own. This is a very diverse phylum, and one that if you become interested in it, could keep you busy for a lifetime of learning. To explore more about molluscs, check out this Introduction to the Molluscs from "Man and Molluscs".

Ohio has a diverse assemblage of molluscs, including a number of rare species.The Ohio Watershed Network's page on freshwater mussels gives a good overview.


The nematodes are the round worms. they differ from the annelids, or segmented worms mainly by a lack of segments in their bodies. They are, as the name says, round, and smooth. Many species of this phylum are microscopic and parasitic. Some researchers have made tremendous headway into using newmatodes to fight plant pathogens and pest species. These nematodes can be very beneficial to humans if properly understood. Other groups of nematodes can cause us problems. Take a look at this listing of parasitic nematodes that attack humans.


Insects, Arachnids, and Crustaceans are all arthropods. The word arthropod is derived from the greek words for "joint" and "foot", arthro, and pod, respectively. These animals have a jointed exoskeleton,a shell which acts as armor. Learn more about arachnids, the spiders, mites and ticks, on the Spider Conservation page. If you are interested in advancing the scientific understanding of spiders, visit the page of the Ohio Spider Survey .

Insects are an enormous group of animals, found in nearly any environment, and impacting nearly every ecological community. Learn more about Common Insects of Ohio from the Cleveland Museum of Natural History.

The Australian Museum online has a page on crustaceans. These arthropods include shrimp, lobster, crabs, crayfish and similar animals.


The phylum Chordata, the Chordates includes animals that have, at some point in their life cycle, a notocord. Our page focuses chiefly on the verebrates, or animals with backbones.

We hope that the information presented here will give you a broader and deeper understanding of Nature, and therefore, of yourself. We make no attempt to be encyclopedic, but if you do find something missing, please feel free to email us at to let us know what you think we should add here.'s feed chicklet's email chicklet's e-newsletter chicklet
Follow eld3esq on Twitter