MORE DETAILED ACCOUNT AT https://flic.kr/s/aHsjLcvd6b
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Relatively delicate shell up to about 10mm high. It has about 5 or 6 whorls with distinct sutures.
Key identification features
Lacuna vincta
1) Columellar groove (“lacuna” or “chink) leading to umbilicus 6Lv flic.kr/p/gTk3By .
2) Well developed spire about 20% of shell height; body whorl about 83% of shell height when 3mm high 4Lv flic.kr/p/gTkQmP , about 79% when 10mm high 1Lv flic.kr/p/gTkbej
3) Body whorl has four brown spiral bands, basal pair easily overlooked if base of shell not examined 9Lv flic.kr/p/gTkQcF .
4) Body whitish with grey; may also have yellow, orange, aquamarine or verdigris parts 18Lv flic.kr/p/gTk92o .
Similar species
Lacuna parva
1) Columellar groove (“lacuna” or “chink) leading to umbilicus flic.kr/p/gUSLhj .
2) Small spire; < 10% of shell height flic.kr/p/gUSLj3 .
3) Body whorl has three brown spiral bands, basal band easily overlooked if base of shell not examined flic.kr/p/gUSL2E Band 2 often wider than band 1 & 3. Some uniformly white flic.kr/p/gUSLj3 or brown with no bands.
4) Body translucent white, sprayed grey. No other colours except yellowish snout, and viscera showing through flic.kr/p/gUSLeU
Lacuna pallidula
1) Columellar groove (“lacuna” or “chink) leading to umbilicus flic.kr/p/gVXJHF .
2) Hardly any spire protrudes from body whorl; very large ‘D’ shape aperture flic.kr/p/gVWR5y .
3) Adult shell greenish-yellow flic.kr/p/gVXJGi ; juveniles yellow or whitish; no spiral bands.
4) Body white flic.kr/p/gVYn9Y, sometimes sprayed grey flic.kr/p/gVXJHF . Sometimes pink flic.kr/p/gVXJGi .
Lacuna crassior
1) Wide white columellar shelf, but usually no groove or umbilicus flic.kr/p/gW3C7X ; sometimes small ones present.
2) Distinct spire about 25% of adult shell height; body whorl about 75% of shell height flic.kr/p/gW3C7X .
3) Shell when live, translucent, yellowish-brown spire, brownish-white body whorl and thick periostracum raised in distinct transverse (costal) ridges Lc flic.kr/p/gW4tzx . Dead shell, dull yellowish-brown if periostracum retained flic.kr/p/gW3CbK , yellowish white with faint spiral lines if periostracum worn off www.aphotomarine.com/snail_lacuna_crassior_thick.html .
4) Body translucent whitish flic.kr/p/gW4tzx .
Cingula trifasciata
Height of shell less than 4.3mm. In winter all, or most, L. vincta are bigger than C. trifasciata https://flic.kr/p/2d4RKAH . In summer L. vincta are rarely bigger than adult C. trifasciata https://flic.kr/p/2cZuiUu .
2) Solid, long, conical spire with almost straight sided profile.
1) No umbilicus or chink. https://flic.kr/p/ftEPif
3) Usually three brown or red-brown spiral bands on body whorl https://flic.kr/p/ftEPfj (one at columella an incomplete turn https://flic.kr/p/ftEPif ).
Single small metapodial tentacle extends from under operculum https://flic.kr/p/ftEPcw .
In crevices or under stones with silt, not on algae.
Gregarious, all sizes found together.
Often near high water mark, but all other levels also, including pools near LWS.