Buddy,

As you recall, annulus is “little ring” etymologically.

And for the biologically inclined:

5 (a) of fungi : a membranous or fleshy ring that surrounds the stipe of certain agarics after the expansion of the pileus : the remnant of the veil (b) of a moss : an elastic ring of cells between the operculum and the mouth of the capsule (c) of a fern : a line of cells partly or entirely surrounding the sporangium and each having inner tangential and radial walls thickened and outer wall thin and by its contraction bringing about rupture of the sporangium and assisting in spore discharge (d) : the fleshy rim of the corolla in some asclepiads (as of the genus Stapelia) (e) : the calyxlike whorl at the base of the strobilus of some horsetails (genus Equisetum)
6 (a) : one of the ringlike but not truly segmented parts of the body of some annelids (as leeches) (b) : ANNUAL RING 2

(cribbed from Webster’s)

Jamie Irons