Emarginate

Definition

Having a margin that is notched, indented, or cut away at a localized point, typically at the apex or midpoint, rather than evenly rounded or entire. In arthropod morphology, describes structures—commonly eyes, elytra, wings, tergites, or genital plates—with a shallow to deep V-shaped or U-shaped excision that does not reach the base. Distinguished from 'truncate' (appearing cut off straight) and 'sinuate' (wavy margin without a discrete notch).

Etymology

Latin emarginatus, from e- 'out' + marginare 'to mark with a margin', referring to the removal or cutting out of a marginal portion.

Example

The emarginate eyes of certain wolf spiders (Lycosidae) feature a distinct anterior indentation that accommodates the base of the chelicerae; in some ground beetles (Carabidae), the elytral apices are emarginate, leaving the terminal abdominal tergites partially exposed.

Synonyms

• notched
• indented

Related Terms

• sinuate
• Truncate
• entire
• emargination
• apex
• elytron
• compound eye

Usage Notes

In entomological descriptions, 'emarginate' is more specific than merely 'notched'—it implies a single, relatively symmetric indentation rather than irregular teeth or serrations. The term is absolute (a structure is or is not emarginate) but admits degrees: 'shallowly emarginate' versus 'deeply emarginate.' Contrast with 'bifid' or 'bifurcate,' where the structure is split into two distinct lobes rather than merely indented. In spider taxonomy, eye emargination is a diagnostic character at genus and species levels.