Flabellum

Definition

A fan-shaped anatomical structure. In arthropod morphology, specifically a flattened, fan-shaped distal expansion on the fifth walking legs (opisthosomal appendages) of horseshoe crabs (Xiphosura), used for pushing through sediment and assisting in locomotion. In cnidarian systematics, also a genus of deep-sea cup corals (Scleractinia, Flabellidae) with flabellate (fan-shaped) corallum morphology.

Etymology

Latin flabellum, diminutive of flabrum 'fan', from flare 'to blow'

Example

The flabellum of Limulus polyphemus bears a fringe of marginal setae that help the animal gain purchase on soft substrates while moving along the seafloor.

Synonyms

• fan (colloquial, non-technical)

Related Terms

• Xiphosura
• opisthosoma
• Telson
• book gills
• uropod
• corallum
• Scleractinia

Usage Notes

In arthropod contexts, 'flabellum' specifically denotes the fan-shaped leg modification in horseshoe crabs and should not be confused with the similarly named but structurally distinct flabellate antennae found in some insect groups (e.g., certain scarab beetles, where 'flabellate' describes lamellate clubbing). The term is homonymous with the cnidarian genus Flabellum, but these usages belong to separate disciplinary vocabularies. No singular/plural distinction is typically marked in anatomical descriptions; 'flabella' appears rarely.