The operculum has a straight columellar-parietal edge (1). Palatal edge is curved (2) except for a straight basal section (3) which, with the columellar-parietal edge, forms a wedge which fits into the siphonal canal. The outer face (right), made of conchiolin produced by the opercular groove, has a marginal nucleus (4) with many fine, surrounding, concentric growth lines. The inner face (left) has a non-marginal, excentric nucleus (5) surrounded by broad, concentric, bands of adventitious conchiolin produced by a ring of gland cells in the opercular disc. The inner face has an area of rougher texture (6) where the columellar muscle attaches to it. The edge of the attachment area is visible as a curved groove (7) unaligned with either growth lines or adventitious bands.
Portland Harbour, Dorset, England, April 2012.
: flic.kr/p/2op3qCC
Sets of OTHER SPECIES:
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