Intermediate valve v from 29 mm long chiton. LWS. Isle of Lewis, Scotland. April 2018. Leg. D.M. McKay & S.Taylor.
The lateral area (1) is very slightly raised and separated from the central area (2) by a shallow, unobtrusive, diagonal depression (3 to 3).
Canals permeate the tegmentum and terminate on its dorsal surface on a minute stipple of caps. (Visible in this magnified image of a cleaned valve, but surface seems smooth to naked eye; at least 3X magnification and cleaned valve needed).
Aesthetes (sensory tissue) fill the canals and perform as sensory organs on the dorsal surface of valves.

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