Tonicella marmorea on left, animal length 29 mm, leg. S. Taylor & D. W. McKay, Lewis 2018.
Boreochiton ruber on right, at same scale, animal length 14.5 mm, leg. P. Lightfoot, N. Yorkshire, 2014.
1: dorsal surface of girdle (perinotum) on T. marmorea has widely spaced, minute granules/ spicules. Usually escape notice in photographs.
2: dorsal surface of girdle (perinotum) on B. ruber has club-shaped spicules with densely-packed, touching heads giving a mealy appearance.
3: marginal fringe of spicules can often be detected on B. ruber but difficult to see on T. marmorea.

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