The anal opening is always on a sclerotized shield. The most basic of such shields is an anal shield—which bears only the opening, the 3 circumanal setaecircumanal setae:
in Mesostigmata, the three setae (postanal and pair of peranal) setae surrounding the anal opening.
(2 pa and an unpaired po), and other circumanal structures such as the cribrumcribrum:
the spiculate area posterior to and often lateral to the anal opening on the shield bearing the anal opening and circumanal setae in Mesostigmata.. If the anal shield is expanded such that some of the ventral setaeventral setae:
in the Lindquist-Evans system used in the Mesostigmata, the ventral region has up to three longitudinal rows (Jv, Zv, Lv) with 1-5 transverse row designations.
(JV, ZV series) are captured, then the shield is called ventrianal. The shape of the ventrianal shieldventrianal shield:
in Mesostigmata, a ventral shield bearing the anal opening, circum anal setae, and one or more pairs of ventral setae or pores (lyrifissures) [see anal shield]; maybe rather narrow or very broad and covering most of the gaster. and the size of the anal opening (fluid-feeding predators have small openings, particulate-feeding omnivores have large openings) are sometimes useful in identification.
Author: David E. Walter
Content last updated Sept. 2006, unless indicated otherwise
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