Dicondylia

Definition

A clade of insects comprising all living species except the jumping bristletails (Archaeognatha), united by the derived trait of dicondylic mandibles—mandibles attached to the head capsule by two articulatory condyles (hinges) rather than the single condyle (monocondylic) characteristic of the earliest insect lineages. The clade includes the wingless silverfish and allies (Zygentoma, sometimes termed 'basal Dicondylia') and the winged insects (Pterygota). Despite the name, Archaeognatha do possess two mandibular condyles, though their structure differs from the 'true' dicondylic condition of Dicondylia.

Etymology

From Greek dikondylos ('two-jointed' or 'two-knobbed'), referring to the paired condyles of the mandibular articulation.

Example

A firebrat (Thermobia domestica, order Zygentoma) is a representative of basal Dicondylia, whereas a honey bee (Apis mellifera, order Hymenoptera) belongs to the derived Pterygota—both are Dicondylia, but only the bee has wings.

Related Terms

• Archaeognatha
• Monocondylia
• Zygentoma
• Pterygota
• dicondylic
• Mandible
• Condyle
• Thysanura

Usage Notes

The term is primarily morphological in origin but used cladistically. Some sources treat Dicondylia as a subclass with Zygentoma as its sole order; others use it informally for the clade uniting Zygentoma + Pterygota. The monocondylic mandible is hypothetical for insects—Archaeognatha are not truly monocondylic—so Dicondylia marks a structural divergence rather than a simple presence/absence character. Contrast with 'Monocondylia,' sometimes used for Archaeognatha alone.