Supernumerary

Definition

Present in excess of the normal or typical number; describing structures, segments, or appendages that exceed the standard count for the taxon. In arthropods, supernumerary structures arise through developmental anomalies, regeneration, or genetic variation and are distinguished from serial homologues or normal polypody by their irregular occurrence and non-repeating pattern.

Etymology

Latin supernumerarius, from super- (above, beyond) + numerus (number), originally referring to extra soldiers beyond the standard legion count.

Example

A tarantula with a supernumerary tarsus on one leg, or a beetle larva bearing an extra pair of spiracles on an abnormal segment, represents a developmental departure from the fixed segmental plan typical of the order.

Synonyms

• accessory
• supplementary

Related Terms

• aberrant
• teratology
• polypody
• Regeneration
• homeotic
• ectopic

Usage Notes

Contrasts with 'rudimentary' or 'vestigial' (reduced below typical number). In taxonomy, supernumerary teeth, vertebrae, or leg segments must be distinguished from normal intraspecific variation; entomologists typically record such anomalies as teratological specimens. The term implies abnormality rather than meristic variation within normal range. Not used for standard additional structures in polypodous groups (e.g., the many legs of a centipede are not 'supernumerary').