Length 32 mm. Inset: enlarged valve viii. LWS. Isle of Lewis, Scotland. April 2018. Leg. D.W. McKay & S.Taylor
Apart from near-rectangular, distinct growth lines, dorsal surface of valves appears smooth to naked eye, but at over X3 (hand lens), numerous distinct small granules visible on cleaned, dry valve (see 18 Tonicella marmorea ). Granules usually not discernible in underwater images or on specimens before deposits and properiostracum removed, but debris or epiphytic growths may be mistaken for them.
Mucro (1): the steep postmucronal slope on valve viii is straight in lateral profile (2) .
The articulamentum insertion plates at the ends of the valves are embedded out of sight into the peripheral girdle. The cuticle on the dorsal surface of the girdle (‘perinotum’) appears leathery-smooth to the naked eye, but strong magnification shows a covering of very small spicules (see 40 Tonicella marmorea & 41 Tonicella marmorea ).
06 Tonicella marmorea
