Annulus (or anulus), being the Latin and French for "ring", is a term used to describe various ring or circle shaped objects (or openings):

  • Annulus (entomology), an antennal unit in simple antennae, or a ring-like marking or structure surrounding a joint or segment.
  • Annulus (Herpetology), reference to too small an opening that can be a potential death trap for a reptile that can't pass through. The size difference of the two cylindrical forms (The body of the animal vs. the circumference of the opening).
  • Annulus (geology), the opening between an outer and inner cylindrical body, often used to describe the space between the well screen or drill pipe and the surface of the bore hole.
  • Annulus (anatomy) refers to several structures in human anatomy. The spelling "anulus" is preferred under Terminologia Anatomica, but both spellings are commonly found. Examples include:
  • Annulus (ichthyology), the annual rings that form in fish scales or bone sections
  • Annulus (mycology), the "ring" on a mushroom stem
  • Annulus (astronomy), the ring of light from the visible part of the photosphere seen at the greatest extent of an annular eclipse
  • Annulus (cosmology), the ring around the lens on which strong gravitationally lensed images of one source appear
  • Annulus (mathematics), a ring-shaped geometric figure
  • Annulus (firestop), the space in a penetration seal surrounding a penetrant, i.e. between a pipe or electrical conduit, or cable and a sleeve, with or without a firestop
  • Annulus (oil well), the tube shaped void between a pipe string and a surrounding pipe string or formation.
  • Annulus (microscopy), a circular opening "disk" below a specimen slide, required for Phase Contrast microscopy
  • Annular hurricane, a hurricane that is nearly symmetrical and takes longer to weaken than normal hurricanes.


Sharp, J. M., Jr., 1999, A Glossary of Hydrogeological Terms: The University of Texas, Austin, Texas

Principles of Contaminant Hydrogeology - Google Books Resultby Christopher M. Palmer - 1996 - Science - 256 pages

Schnirel, Brian - Leeway Corucia Research Center (LCRC), 2008 Watching for potential death traps The Official Discussion Board of the American Association of Zoo Keepers ... General discussion forum.

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