Most monogynaspids have an anal opening with a
pair of anterior valves and an unpaired posteriorposterior:
the back part of the body or towards that region in comparison, e.g., 'posterior to'.
valve.
Some have only the anterior pair of valves, but
only in Zerconidae will the anal valves have setae after the larval stagestage:
a distinct developmental form, e.g., the egg, larval, nymphal and adult stages. Since mite instars are usually morphologically distinct, they are also stages (and see stase). Some authors, however, insist that instar should be apolysis to apolysis and stage ecdysis to ecdysis. Since apolysis can be a discontinuous process and, in any case, is difficult to determine, in practice the difference between a stage and an instar is abstract and of importance only if you have a contentious referee.
A few groups of Mesostigmata have evolved the ability to ingest fungal hyphae and spores. These particulate-feeders have enlarged anal openings that allow the passage of solid waste. A good clue to this adaptation is the presence of fungal material in the guts of the animal (not to be confused with adhering spores, etc.).
Author: David E. Walter
Content last updated Sept. 2006, unless indicated otherwise
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