Muscles controlling valve movement. Orkney, Scotland. February 2015. Leg. P. Lightfoot per J. Porter.
Four sets of muscles articulate individual valves to conform closely to uneven rock surface:
1: attachment points of pair of lateral muscles that connect the foot to each end of the valves, one on each side of the slit. (Muscles removed, visible on 38 Tonicella marmorea and 50 Tonicella marmorea )
2: pair of straight muscles pass along the jugum, attaching to the anterior margin of the jugal sinus of each valve and to the body wall under the previous valve.
3: on each side of a valve an oblique muscle is attached to the jugal sinus close to the straight muscle and travels anteriorly outwards under the diagonal line that separates the lateral area of the tegmentum from its central area. The anterior end of the muscle attaches to the body wall under the preceding valve on which it leaves a comma shaped scar (see 03 Tonicella marmorea .)
4: The transverse muscle consists of dorso-ventral fibres connecting the apophyses of one valve to the underside of the preceding valve. Muscle colour is often the same as that of the jugal tract; white, yellow or pink (see 52 Tonicella marmorea ).
See also images 38 Tonicella marmorea , & 50 Tonicella marmorea .
51 Tonicella marmorea
