Who's Who - Insects and Allies

Taxonomy and Arthropod Characteristics

DEFINITIONS
 

Binomial Nomeclature System	-	two part naming system (naming with 2 names) used for all biological types or species. First name is the genus and is always capitalized, second name is the species. Written binomial names are either italicized or underlined.
Classification	-	process of dividing and subdividing into a system of categories or ranks.
Phylum	-	a major rank or classification containing similar organisms. Humans are in the phyla Cordata, animals with dorsal nerve chords. Most Cordata have a backbone.
Species	-	the fundamental unit of classification, distinct type of organism, usually further defined as being reproductively isolated from other species.
Taxonomy	-	the science of classifications and the basis or bases for classification.

Classification Categories

Link to Tree of Life - Arthropoda

Phylum Arthropoda - Characteristics

1. EXOSKELETON In most arthropods the body is covered with chitonous cuticle that is hardened into an exoskeleton. In crustacea and millipedes, the cuticle is hardened by the addition of calcium; in insects, the cuticle is tanned, chemically bonded with protein. Once the cuticle is hardened it can not increase in size. Some regions of the cuticle remain unhardened to allow flexibility and movement.
 

2. METAMERISMBody composed of numerous segments (somites), segmented condition may be concealed. In the primitive Arthropod, the body was thought to be a series of metameres, each, except for the first and last, with a pair of appendages. Metamerism is an example of an important biological trait, that of replication and modification to develop new traits and capabilities.

3. JOINTED APPENDAGESJointed appendages give arthropods numerous, generalized appendages which were modified into numerous specialized organs for walking, grasping, and eating.

4. DOUBLE VENTRAL NERVE COR Ventral nerve cord with ganglia(swellings) at each segment. Only the brain (most anterior) ganglia is above the digestive system.

5. OPEN CIRCULATORY SYSTEM A dorsal (upper) vessel directs blood forward toward the brain, an open system allows the blood to circulate back through the body.
 
 

6. BILATERAL SYMMETRY Body can be divided into two equal halves through one plane. Most animal groups that are very active are bilaterally symmetrical. But not all animals have bilateral symmetry, some have radial symmetry, e.g.. jellyfish.

7. SEXUAL REPRODUCTION Sexual reproduction or the uniting of female and male gametes is the usual case in arthropods. However, some insects are parthenogenic, females produce female offspring without mating. In the Hymenoptera (bees and wasps) haplodiploidy is common. An example is the honey bee where the queen bee stores sperm and selectively fertilizes her eggs, unfertilized eggs develop into males and fertilized eggs develop into females.

Phylum Arthropoda - Extant Groups

CLASS INSECTA Insects (derivation: in=into, sect=cut; 750,000 known species). Link to Tree of Life - Insecta

• Single pair of antenna
• Three body regions (head, thorax, and abdomen)
• Three pairs of legs (adult insect), one on each segment of thorax
• Most adult insects with wings

CLASS CRUSTACEA Shrimp, lobsters, and crabs (derivation: crust=hard, shell-like; 26,000 known species). Link to Tree of Life - Crustacea.

• Two pairs of antennae
• Two body regions (head and thorax combined into the cephalothorax)
• One pair of appendages per body segment. Appendages terminate in pinchers.
• Primarily an aquatic group, respiration is by gills even in terrestrial species.
• Some very unusual groups, for example, barnacles and water fleas

CLASS DIPLOPODA. Millipedes (derivation: diplo=two, poda=feet; 8,000 known species).

• Single pair of antennae
• Two body regions, head and body
• Body segments fused in pairs, each apparent segment composed of two embryonic segments
• Two pairs of appendages per apparent body segment, extending out from sides of body
• Detritivore

CLASS CHILOPODA. Centipedes (derivation: chilo=lip, poda=feet; 3,000 known species).

• Single pair of antennae
• Two body regions, head and body
• One pair of legs per body segment
• Appendages of first body segment modified into poisonous claws
• Predacious

CLASS ARACHNIDA. Spiders, ticks, mites, scorpions, horseshoe crabs (derivation: arachne=spider; 57,000 known species). Link to Tree of Life - Arachnida.

• No antennae
• Most with a cephalothorax and abdomen. Some with a single body region.
• Most are terrestrial
• Most are predacious.

Tree of Life Pterygota , winged insects (pterygos = wing), and Endopterygota, insects with internal wing buds during their immature stages (endo = within, pterygos = wing) . The Endopterygota have distinctive larval, pupal, and adult stages. They are also called the Holometabola, referring to the "complete metamorphosis" of the insects in this group.

Insect Drawings at Illinois This is a page within the University of Illinois, Department of Entomology WEB site. It contains a collection of 34 (as of 2/1/95) original line drawings mainly covering the major insect orders. Some are of individual families and species and their life cycles. Each drawing also has a pointer to a corresponding site in the Tree of Life at the University of Arizona.

Some of the drawings at the University of Illinois have errors or are misleading. For example the termite drawing also contains a series of ant pictures. The original purpose was probably to contrast the metamorphosis of the termites (incomplete) with that of ants (complete). The errors are discussed in an errata section.

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Last updated Dec. 30, 2000