Definition

A median, usually posteriorly projecting structure arising from the tenth abdominal tergite in certain insects; homologous with the dorsal part of the eleventh abdominal segment in more basal hexapods. In Odonata it forms a small triangular plate between the cerci, while in Archaeognatha (bristletails) it is greatly elongated as a central caudal filament, often longer than the paired lateral cerci and paraprocts.

Etymology

Greek epi- (upon, above) + proktos (anus)

Example

In the sea bristletail Petrobius maritimus, the epiproct appears as the longest of the three tail filaments, flanked by the shorter paired cerci.

Related Terms

• cercus
• paraproct
• abdominal segment
• tergite
• pygopod
• Archaeognatha
• Odonata
• caudal filament

Usage Notes

The epiproct is distinguished from the cerci by its median (unpaired) origin and from the paraprocts (ventral appendages of segment 11) by its dorsal position. Presence and form vary markedly across insect orders: reduced or absent in most Neoptera, conspicuous in basal lineages. Not to be confused with the subgenital plate or other genital structures. In some literature, particularly older texts, the term may be used more loosely for any median terminal appendage.