Classification of Arthropods
The Insecta (insects) are a Class of the large animal Phylum
called ARTHROPODA (arthropods) - a name that refers to the jointed limbs. The other major Classes of living arthropods
(i.e. animals related to insects) include the Crustacea (crabs, lobsters, shrimps, barnacles, woodlice, etc.), the
Myriapoda (millipedes, centipedes, etc.) and the Arachnida (scorpions, king crabs, spiders, mites, ticks, etc.).
In addition there are several minor Classes, the Onychophora (velvet worms), Tardigrada (water bears),
Pentastomida (tongue worms) and Pycnogonida (sea spiders), all of which contain somewhat aberrant living forms
of uncertain affinities to the any of the preceding groups, and finally a Class of extinct arthropods, the Trilobita
(trilobites), known only from their fossil remains. All these animals are characterised by a tough outer body-shell or
exoskeleton, with flexible joints between the skeletal plates to allow the animal to move.
The main external body features which distinguish each of the four
major Classes of living arthropods, Crustacea, Myriapoda, Arachnida and Insecta, are shown below (with those that separate
the insects from all other groups highlighted in red).
MAIN BODY REGIONS
PAIRS OF LEGS
PAIRS OF ANTENNAE
||two - cephalothorax* and abdomen (some with head and trunk)
||five or more
||two - head and trunk
||many - one or two per trunk segment
||two - cephalothorax* and abdomen
||none (though palps may resemble antennae or legs)
||three - head, thorax and abdomen
||usually present (but many wingless forms)|
|*cephalothorax = fused head and thorax|
Each of the Classes of arthropods, including the insects, are split
into a number of smaller groups, which reflect progressively more detailed structural similarities between the group members.
These smaller groups follow a strict hierarchy. The major class divisions in descending order of size are called Subclass,
Order, Sub-order, Family, Subfamily and Genus. A Genus is the smallest group of any real importance in the naming of individual
species, although in some classifications generic groups may be further split into Sub-genera. The scientific name of a species
includes, first, the Genus to which it belongs and, second, its specific name, e.g. the European Violet Ground Beetle is
called Carabus violaceus, meaning the species violaceus in the genus Carabus (by
convention, generic and specific names are always printed in italics; the generic name spelt with a capital letter and the
specific name with a small letter). The full classification of this insect would be as follows:
Carabus violaceus L.
violet ground beetle
The name of the author who first describes a species, or a recognised
abbreviation of the author's name, is sometimes quoted after the specific name of the animal, in this case L. = Linnaeus (the
Swedish naturalist who firmly established the binomial system for naming animals and plants in 1753, and who published the
first descriptive account of this particular beetle).
Excluding one or two very small groups of shrimps, the crustaceans
are split into 9 main Orders, as listed below. They nearly all live in water and range from minute planktonic shrimp-like
creatures, such as water fleas, to the large, more familiar, crabs and lobsters. Some members of the Isopoda are the only
forms that have really invaded the land and most of these are largely confined to damp places.
||Water Fleas (Daphnia), Fairy, Brine,
Tadpole and Clam Shrimps|
||Water Fleas (Cyclops), Fish Lice,
Gill Maggots and Anchor Worms|
||Shrimps, Prawns, Lobsters, Crayfish and Crabs|
||Freshwater Shrimps (Gammarus) and Sand Hoppers|
||Sea Slaters, Water Slaters, Water Lice and Woodlice|
There are four groups of centipede-like creatures known collectively
as myriapods. These are listed here as Orders of the Class Myriapoda, but in many arthropod classifications they are given the
status of separate Classes.
The arachnids are usually split into 8 main Orders, as listed below.
||King Crabs or Horseshoe Crabs|
|2. Pseudoscorpiones (= Chernetidea)
||Pseudoscorpions or False Scorpions|
|5. Solifuga (= Solpugae)
||Wind Scorpions or Barrel Spiders|
|6. Opiliones (= Phalangidea)
||Harvestmen or Harvest Spiders|
|7. Acari (= Acarina)
||Mites and Ticks|
The insects are generally sub-divided into 29 Orders, as listed
SUBCLASSES & FEATURES
These are wingless insects and their
body structure suggests that they have never had wings during their
evolutionary history. Young stages resemble the adults - little or
These are winged insects, although some
have lost their wings during the course of evolution.When present, the wings
develop externally and there is no marked change (metamorphosis) during the life
cycle. The young stages, called nymphs, resemble the adults except in size and
in lacking fully-developed wings - simple metamorphosis.
||Damselflies and Dragonflies|
||Crickets, Grasshoppers and Locusts|
||Stick and Leaf Insects|
||Cockroaches and Mantids|
||Booklice and Barklice|
|18. Siphunculata (= Anoplura)
||Alder Flies, Snake Flies and Lacewings
These are winged insects, although some
have lost their wings during the course of evolution. When present, the wings
develop internally (i.e. inside the body of the immature insect) and there is
a marked change (metamorphosis) during the life cycle. The young stages are
very different from the adults and are called larvae. The change from larva
to adult takes place during a non-feeding stage called the pupa
(or chrysalis) - complex metamorphosis.
||Butterflies and Moths|
||Sawflies, Ants, Bees and Wasps|