Classification - a brief explanation

Invertebrates are the most numerous and diverse group of animals on earth.

They are cold-blooded creatures with segmented bodies and - because they lack a backbone - a chitinous exoskeleton that protects and holds everything together. It's the absence of the vertebral column that defines an invertebrate, and the primary characteristic feature that separates them from vertebrate species.

This website concentrates on the land-living terrestrial British species that I might encounter locally.

Higher Classification

Perhaps the first thing to appreciate is that invertebrates is a term of convenience, rather than a taxonomic ranking.

They are arthropods of the higher classification ranking of the phylum ARTHROPODA, which is divided into four subphyla:

HEXAPODA

The important subdivision that includes all the insect species, together with springtails, two-pronged bristletails and proturans.

CHELICERATA

A major subdivision that encompasses the arachnids, including spiders, harvestmen, scorpions, mites and ticks.

MYRIAPODA (Myriapods)

The subphylum that includes centipedes and millipedes.

CRUSTACEA (Crustaceans)

A diverse taxon that includes woodlice (ISOPODS) as well as various sea creatures that are not covered here.

Classification used on this website

Whilst the above is useful for a general understanding, they are higher level rankings that don't need to be referenced for each species.

The general term insects refers to the species of the class INSECTA. Their segmented bodies have three parts (head, thorax and abdomen), three pairs of jointed legs, compound eyes, antennae and, without getting into further explanation, one or two pairs of wings.

INSECTA is then divided into ORDERS and that's where the classification used here starts.

There are twenty-five ORDERS of British Insects:

The big five:

HYMENOPTERA

DIPTERA

COLEOPTERA

HEMIPTERA

LEPIDOPTERA

Bees, Wasps, Sawflies and Ants

True Flies

Beetles

Bugs

Butterflies and Moths

Then:

ODONATA

ORTHOPTERA

Dragonflies and Damselflies

Grasshoppers and Crickets

And a number of smaller orders, including:

MECOPTERA

RAPHIDIOPTERA

PLECOPTERA

EPHEMEROPTERA

MEGALOPTERA

TRICHOPTERA

NEUROPTERA

PSOCOPTERA

DERMAPTERA

BLATTODEA

Scorpionflies

Snakeflies

Stoneflies

Mayflies

Alderflies

Caddisflies

Barkflies

Lacewings

Earwigs

Cockroaches

We then have the wingless arthropods that were previously classified with insects, but are now treated as a class in their own right:

COLLEMBOLA

Springtails

Spiders and Harvestmen are arachnids of the class ARACHNIDA. Unlike insects, arachnids have four pairs of legs and two further pairs of appendages called the chelicerae and pedipalps, which respectively aid feeding and defence, and sensory functions. ARACHNIDA includes various ORDERS, but for the purpose of this introduction, the important two are:

ARANEAE

OPILIONES

Spiders

Harvestmen

Rankings applicable to the Myriapods and Isopods will be covered on their respective pages.

Taxonomy

It may have been noted that taxonomic ORDERS are written in capital letters, as are SUBORDERS, or indeed any of the higher ranked taxon. Maintaining consistency when listing the taxonomic classification of species is important as it helps avoid errors or misunderstanding.

It's the larger ORDERS that often need to be subdivided and it's here that you may find SUBORDERS or the use of DIVISIONS or CLADES. Suffice to say that they are used to bridge the taxonomic gap between ORDER and families. That said, there is a taxon above family that is used quite extensively in the classification of larger ORDERS and that is superfamily. Generally, the superfamily, which essentially is a collection of related families, is written in lower case, the same as family and subfamily. A superfamily always ends ...oidea, a family ...idae, and a subfamily ...inae.

As well as needing intermediary taxon between ORDER and family, there is often a need to do likewise between family and genus, which is where subfamilies come into play and, if required, a further subdivision called a tribe. A tribe always ends in ....ini, and is always written in italics.

The species binomial is a two-part name, the first part being the genus, and the second being the species. It should be written in italics wherever possible, with only the Genus capitalised even if the species is derived from a proper name.

Whilst the above is a condensed explanation, I hope it makes sense.

However, it may be easier to understand by looking at a couple of examples with different levels of complexity.

The first example is for the hoverfly Helophilus pendulus, which would be:

DIPTERA > MUSCOMORPHA > LOWER CYCLORRHAPHA - ASCHIZA >

Syrphoidea > Syrphidae > Eristalinae > Eristalini > Helophilus pendulus

This is one of the longest full classifications as DIPTERA (true flies) is such a large order, hence the need for extended higher ranked taxon and both subfamily and tribe, all of which are explained in the DIPTERA gallery write-ups.

The second example is for the scorpionfly Panorpa communis, which is in one of the smallest orders represented in Britain by just three species and where classification couldn't be simpler; ORDER > family > species:

MECOPTERA > Panorpidae > Panorpa communis