Lacuna vincta (Montagu,1803)
Synonyms: Turbo vinctus Montagu,1803; Epheria vincta (Montagu,1803); Lacuna divaricata (Fabricius, 1780).
Current taxonomy: World Register of Marine Species
www.marinespecies.org/aphia.php?p=taxdetails&id=140170
Vernacular: Banded chink shell, Northern Lacuna; Gwichiad agennog rhesog (Welsh); Scheefhorentje (Dutch); Båndtegnet grubesnegl (Danish); Tarestilksnegl (Norwegian); Bandad lagunsnäcka (Swedish); Gebänderte Grübchenschnecke (German); Lacune commune de l’Atlantique (French).

GLOSSARY BELOW
Shell Description
The shell grows up to 10 mm high, or slightly more in northern Scotland and further north 01 Lacuna vincta . It is a spring breeding annual, so the maximum size is usually only found in winter and spring. In the Menai Strait in North Wales, the usual height range is 1mm to 3 mm in July 02 Lacuna vincta , and 3 mm to 6 mm in August 03 Lacuna vincta . The well developed spire is about 50% of adult shell height 01 Lacuna vincta and about 40% of shell height when 3 mm high 04 Lacuna vincta Juveniles less than 3 mm high have small spires of about 30% shell height; so they can be confused with L. parva 02 Lacuna vincta . The apex is fairly sharp, the whorls rounded and the sutures distinct. Very fine spiral lines may be faintly discernible on dead shells when the thin periostracum is worn off 01 Lacuna vincta . Multiple, possibly diurnal, fine, prosocline growth lines 05 Lacuna vincta are often visible on both live and dead shells. One face of the hollow columella is missing, exposing a long columellar groove (lacuna or chink) leading to the umbilicus 06 Lacuna vincta. . The aperture is about 60% of shell height on 3 mm high shells 04 Lacuna vincta , and about 50% when 10 mm high 01 Lacuna vincta . The outer (palatal) lip is curved, except fairly straight at the base where it also everts to make a slight spout 07 Lacuna vincta . The outer lip turns and continues up the abapertural side of the columellar groove 07 Lacuna vincta . The columellar lip is wide, white, slightly curved and forms the adapertural edge of the columellar groove 06 Lacuna vincta. . The parietal lip is a whitish glaze on the body whorl 06 Lacuna vincta. . The adapical angle is about 90° 05 Lacuna vincta . The operculum is a transparent, pale, horn-coloured, ovoid, rapidly expanding spiral 08 Lacuna vincta . The thin periostracum usually extends beyond the aperture-lip flic.kr/p/gTke96 . The ground colour of the shell is white. Its brightness is often dimmed, or it is tinted yellowish, by the translucent periostracum, or it is tinted green by the body within 07 Lacuna vincta . The body whorl has four light-brown to dark-brown spiral bands. The basal two pass into the aperture and are easily overlooked if the base of the shell is not examined 09 Lacuna vincta . The two adapical bands continue onto the next whorl, becoming less distinct on subsequent whorls, and usually indistinguishable on the two most apical whorls. The bands sometimes coalesce into two or three broad ones flic.kr/p/gTk9JW , or fuse to make an all-brown shell but, even then, the form of four bands can often be discerned in good lighting 05 Lacuna vincta . The periostracum often dims the colour of the bands 10 Lacuna vincta .

Body Description
The translucent white flesh is often stippled grey or aquamarine 11 Lacuna vincta . The snout can form a horseshoe-shape or the ventral gap can close to form a cylinder or open into a shallow curve 12 Lacuna vincta . It is yellow or orange, sometimes with aquamarine blotches. Its tip is deeply wrinkled when closed into cylinder. The cephalic tentacles are long, slender and translucent whitish. They, taper to a blunt tip. They are almost smooth 13 Lacuna vincta , but wrinkled when contracted 14Lv 14 Lacuna vincta . Setae are reported on the tentacles by Forbes & Hanley (1853), and shown in line drawing in Fretter & Graham (1962), but are not visible on these macro images. The tentacles are sometimes faintly tinted yellowish or greenish, especially when contracted 15 Lacuna vincta . There is a black eye on a short bulge at the base of each cephalic tentacle flic.kr/p/gTkdGz . The bulge may be tinted aquamarine 17 Lacuna vincta or yellowish. Behind the tentacles, the head shows pink internally with long narrow white “V” dorsally 17 Lacuna vincta . It may be blotched aquamarine. Behind the head, the body is translucent white showing yellow internally, and the surface is sometimes faintly tinted aquamarine 18 Lacuna vincta . The mantle-edge is yellowish. The interior of the mantle cavity is whitish, often with a dense aquamarine 19 Lacuna vincta and/or grey stipple. The mantle is translucent showing the bands on the shell above 20 Lacuna vincta . The ctenidium in the mantle cavity is whitish or tinted as the mantle 21 Lacuna vincta . The foot has a mesopodial groove between its anterior and posterior parts which is sometimes visible on the side of the foot 15 Lacuna vincta and 17 Lacuna vincta . When contracted, the foot forms a figure of eight 22 Lacuna vincta and stops short of the snout. When extended, the foot in front of the mesopodial groove elongates well beyond the snout and retains its well rounded propodium 23 Lacuna vincta and 24 Lacuna vincta . The white dorsal surface of the foot is often distinct from the body above when the latter is grey, yellow or aquamarine 18 Lacuna vincta . The sole is translucent white 22 Lacuna vincta and may be tinted like the body above it 16 Lacuna vincta . The slight medial groove on the sole is seen most easily when the foot is extended 23 Lacuna vincta &Lv 25 Lacuna vincta . A distinct flat metapodial tentacle emerges at each side from the rear of the opercular disc below the operculum 22 Lacuna vincta and sometimes curve upwards 11 Lacuna vincta .

Key identification features
Lacuna vincta
1) Columellar groove (“lacuna” or “chink”) leading to umbilicus 06 Lacuna vincta. .
2) Maximum height about 10 mm. Well developed spire about 50% of adult shell height 01 Lacuna vincta ; about 40% of shell height when 3 mm high 04 Lacuna vincta , but juveniles less than 3 mm high have small spires of about 30% shell height, which can be confused with L. parva02 Lacuna vincta .
3) On apertural-view, the aperture occupies about 50% of area on juveniles 06 Lacuna vincta. and about 30% on full grown adults 01 Lacuna vincta .
4) Body whorl has four brown spiral bands, basal pair easily overlooked if base of shell not examined 09 Lacuna vincta .
5) Body whitish with grey; may also have yellow, orange or aquamarine parts 18 Lacuna vincta .
6) Found on Laminaria and, especially juveniles, on small red weeds. Also on Zostera and sometimes on fucoids.

Similar species
Lacuna parva (da Costa, 1778)
1) Columellar groove (“lacuna” or “chink) leading to umbilicus 26 Lacuna vincta COMPARE Lacuna parva .
2) Usual maximum height 4 mm; sometimes 6 mm. Spire 30% to 40% of shell height. 26 Lacuna vincta COMPARE Lacuna parva , 27 Lacuna vincta COMPARE Lacuna parva , & 29 Lacuna vincta COMPARE Lacuna parva .
3) On apertural-view images, aperture occupies about 50% of area 26 Lacuna vincta COMPARE Lacuna parva .
4) Body whorl has three brown spiral bands, basal band 1 easily overlooked if base of shell not examined fig.28 28 Lacuna vincta COMPARE Lacuna parva . Band 2 often wider than bands 1 and 3. Some shells are uniform white 29 Lacuna vincta COMPARE Lacuna parva or brown with no bands.
5) Body translucent white, often stippled grey. No other colours except yellowish snout, and viscera showing through 30 Lacuna vincta COMPARE Lacuna parva .
6) Found mainly, especially when young, on small red weeds. Sometimes on fucoids.

Lacuna pallidula (da Costa, 1778)
1) Columellar groove (“lacuna” or “chink) leading to umbilicus 31 Lacuna vincta COMPARE Lacuna pallidula but sometimes sealed over 32 Lacuna vincta COMPARE Lacuna pallidula .
2) Maximum heights female 12 mm, male 6 mm. Hardly any of the spire protrudes beyond the body whorl 31 Lacuna vincta COMPARE Lacuna pallidula and 33 Lacuna vincta COMPARE Lacuna pallidula .
3) Very large ‘D’ shape aperture occupies about 75% of area in apertural view 31 Lacuna vincta COMPARE Lacuna pallidula and 32 Lacuna vincta COMPARE Lacuna pallidula .
4) Shell greenish-yellow with no spiral bands 32 Lacuna vincta COMPARE Lacuna pallidula and 33 Lacuna vincta COMPARE Lacuna pallidula .
5) Body white 32 Lacuna vincta COMPARE Lacuna pallidula , sometimes yellowish or pinkish; no grey stipple.
6) Found mainly on Fucus serratus and sometimes on Laminaria.

Lacuna crassior (Montagu, 1803)
1) Wide white columellar shelf, but usually no groove or umbilicus 34 Lacuna vincta COMPARE Lacuna crassior ; sometimes small ones present.
2) Distinct spire about 50% of mature shell height, about 45% when younger 36 Lacuna vincta COMPARE Lacuna crassior .
3) Aperture occupies about 30% of area in apertural view 34 Lacuna vincta COMPARE Lacuna crassior .
4) Shell when live, translucent, yellowish-brown spire, brownish-white body whorl and thick periostracum raised in distinct transverse (costal) ridges 35 Lacuna vincta COMPARE Lacuna crassior . Dead dry shell, dull yellowish-brown if periostracum retained 36 Lacuna vincta COMPARE Lacuna crassior , yellowish white with faint spiral lines if periostracum worn off.
5) Body translucent whitish 35 Lacuna vincta COMPARE Lacuna crassior .
6) A rare species which often associates with the bryozoan Alcyonidium diaphanum.

Cingula trifasciata (J. Adams, 1800)
1) No umbilicus or columellar groove 37 Lacuna vincta COMPARE Cingula trifasciata .
2) High, conical spire with almost straight sided profile.
Maximum height 4.3 mm. In winter L. vincta are bigger than C. trifasciata but in summer they are a similar size to, or smaller than, adult C. trifasciata 38 Lacuna vincta COMPARE Cingula semifasciata .
3) Aperture occupies about 25% of area in apertural view 37 Lacuna vincta COMPARE Cingula trifasciata .
4) Usually three brown or red-brown spiral bands on body whorl 37 Lacuna vincta COMPARE Cingula trifasciata .
5) Body translucent whitish stippled with opaque white 39 Lacuna vincta COMPARE Cingula trifasciata .
6) Usually found in silt under stones or in crevices.

Barleeia unifasciata (Montagu, 1803).
1) No umbilicus or columellar groove 40 Lacuna vincta COMPARE Barleeia unifasciata .
2) Well developed spire height about 60% of shell height.
Maximum height 3 mm. In winter L. vincta are bigger than B. unifasciata but in summer the smallest juvenile L. vincta may be a similar height to adult B. unifasciata40 Lacuna vincta COMPARE Barleeia unifasciata .
3) Aperture occupies about 25% of area in apertural view 40 Lacuna vincta COMPARE Barleeia unifasciata .
4) Usually all red-brown or with a single wide red-brown spiral band on body whorl 40 Lacuna vincta COMPARE Barleeia unifasciata ; occasionally band splits into two.
5) Body and foot translucent whitish, operculum black-ruby 41 Lacuna vincta COMPARE Barleeia unifasciata . Head light-brown to black-brown; patch behind eyes and line along tentacles bright yellow 42 Lacuna vincta COMPARE Barleeia unifasciata .
6) Found under stones or in fine red weed, especially Corallina.

Habits and ecology
L. vincta feeds on algae, including Laminaria, Fucus, Zostera, Ceramium, Phycodrys rubens03 Lacuna vincta , Polysiphonia, Cryptopleura ramosa43 Lacuna vincta and Chordaria at LWS on rocky shores (and sandy ones where Zostera grows) and to about 35 m depth, varying with light penetration sufficient to sustain food-algae. It is absent from shores where turbidity prevents algal growth at LWS. Usually, juveniles feed on smaller, softer algal species, moving onto the larger tougher Laminaria when adult 44 Lacuna vincta . When large numbers are involved, frequent in northern Britain, great amounts of alga may be destroyed by them, including the severing of tough Laminaria stipes 45 Lacuna vincta ; often in combination with Patella pellucida which may make the initial breach. Other species with weaker radulae sometimes avail themselves of the breaches made by L. vincta and P. pellucida44 Lacuna vincta .
It can live in brackish water with salinity greater than 12 ‰. It travels with a jerky bipedal stepping motion, lifting alternately right and left sides of the foot on either side of a central groove 23 Lacuna vincta . An opaque, anterior pedal gland 25 Lacuna vincta secretes lubricating mucus from the bilaminate edge of the propodium as it travels. Glands on either side of the sole also exude secretions. Security against being swept away, and help with vertical movement among weed, is provided by a string of mucus secreted by the posterior pedal gland. At the approach of a predatory Asterias rubens, L. vincta wave their sensory tentacles vigorously, perhaps to maximize the detection of its odour (external videos) flic.kr/p/29evCJH & 48 Lacuna vincta . They also rotate their shells rapidly which probably hinders the tube feet of the A. rubens from getting a firm grip. The instant a L. vincta is touched by a tube foot, it releases its grip of the weed to let itself fall and escape. The rapid tumbling fall suggests that in an emergency it makes a last ditch free-fall without pausing to produce a mucus string. It breeds from January to May in Britain. Spawn is deposited in distinctive gelatinous rings, usually white or yellow, occasionally green or pink, containing 1000 to 1200 ova 46 Lacuna vincta . After 2 to 3 weeks, the ova swell and burst releasing veliger larvae which form a common constituent of the plankton. All adults die after breeding, so only juveniles are found in summer 02 Lacuna vincta .

Distribution and status
L. vincta is a boreal species found in the north-west and north-east Atlantic and in the north east Pacific from the Arctic to Brittany, New England (USA) and northern California. GBIF map www.gbif.org/species/2301175 It is found all around Britain and Ireland where conditions permit growth of food-algae. It is commonest in the north; southern England is nearly the southern limit of its distribution in Europe. NBN UK distribution map species.nbnatlas.org/species/NBNSYS0000175977
Acknowledgements
I thank George Brown and Chris Rickard for use of their informative images and videos, and Russell Wyeth for helpful discussion.

References and links
Callomon, P. 2019. Standard views for imaging mollusk shells. American Malacological Society. www.researchgate.net/publication/331044326_Standard_views…

Forbes, E. & Hanley S. 1849-53. A history of the British mollusca and their shells. vol. 3 (1853), London, van Voorst. archive.org/details/historyofbritish03forbe/page/62/mode/1up

Fretter, V. and Graham, A. 1962. British prosobranch molluscs. London, Ray Society.

Graham, A. 1988. Molluscs: prosobranch and pyramidellid gastropods. Synopses of the British Fauna (New Series) no.2 (Second edition). Leiden, E.J.Brill/Dr. W. Backhuys. pp.662

Oliver, P.G., Morgenroth, H. & Salvador, A. 2017. Type specimens of Mollusca described by Col. George Montagu in the Royal Albert Memorial Museum & Art Gallery, Exeter and the Natural History Museum, London. Zoosystematics and Evolution. 93(2). pp.363-412
gbmolluscatypes.ac.uk/specimens/168

Jeffreys, J.G. 1862-69. British conchology. vol. 3 (1865). London, van Voorst. (As Lacuna divaricata); archive.org/details/britishconcholog03jeffr/page/346/mode…

Wyeth, R.C., 2019. Olfactory navigation in aquatic gastropods. Journal of Experimental Biology 222 (Suppl. 1): jeb185843. journals.biologists.com/jeb/article/222/Suppl_1/jeb185843…

Glossary
‰ = parts salt per thousand parts water (marine salinity 30‰ and above).
aperture = mouth of gastropod shell; outlet for head and foot.
apical = at the apex.
abapertural = away from the aperture.
abapical = away from the apex of the shell.
adapertural = towards the aperture.
adapical = towards the apex of the shell.
aquamarine = blue-green, sometime colour of sea.
chink = (see columellar groove).
columella = solid or hollow axial “little column” around which gastropod shell spirals; hidden inside shell, except on final whorl next to lower part of inner lip of aperture where hollow ones may end in an umbilicus or siphonal canal.

columellar = (adj.) of or near central axis of spiral gastropod,
columellar groove = groove where one face of hollow columella missing, leads to umbilicus. Also called “lacuna” or “chink.

columellar lip = lower (abapical) part of inner lip of aperture.
cephalic = (adj.) of the head.
costa = strong rib running across a whorl of a gastropod shell.
costae = strong ribs running across a whorl of a gastropod shell.
costal = (adj.) of, or positioned as, costa running across whorl of gastropod shell.
ctenidium = comb-like molluscan gill; usually an axis with a row of filaments either side.
ctenidia = (pl.) comb-like molluscan gills; usually an axis with a row of filaments either side.
diurnal = daily, of each day.
ELWS = extreme low water spring tide (usually near March and September equinoxes).
EHWS = extreme high water spring tide (usually near March and September equinoxes).
height = (of gastropod shells) distance from apex of spire to base of aperture.
lacuna = (see columellar groove).
LWS = low water spring tide, two periods of a few days each month when tide falls lowest.
mantle = sheet of tissue that secretes the shell and forms a cavity for the gill in most marine molluscs.
MHW = mean high water level.
MHWS = mean high water spring tide level (level reached by highest tides for a few days every fortnight, Pelvetia zone on rocky coasts).
MTL = mid tide level.
mesopodial = (adj.) of the middle section of the foot.
mesopodium = middle section of the foot.
metapodial = (adj.) on or of the metapodium (hind part of foot).
metapodium = hind part of the foot.
operculum = horny plate, sometimes calcareous, used to close shell aperture.

palatal lip = outer lip of gastropod aperture.
parietal lip = upper (adapical) part of inner lip of gastropod aperture that lies, often as a glaze, on surface of whorl.

periostracum = thin horny layer of chitinous material often coating shells.
periostracal flap = extension of periostracum as flexible flap beyond outer lip of gastropod aperture.

prosocline = (of aperture rim and growth lines) leaning forwards relative to the direction of shell growth.

plankton = animals and plants that drift in pelagic zone (main body of water).
propodial = at the front of the foot.
prosocline = (adj. of line or sculpture) obliquely across snail whorl with end nearest apex tilted towards aperture.

protoconch = apical whorls produced during embryonic and larval stages of gastropod; often different in form from other whorls.

radula = ribbon of chitinous teeth extruded on a tongue-like structure (odontophore) to rasp food.
seta = (pl. setae) a structure resembling a hair or a bristle.
spire height = distance from apex to adapical angle of aperture.
suture = groove or line where whorls adjoin.
umbilicus = cavity up axis of some gastropods. Sometimes open as a hole next to columellar lip of aperture or at apex if eroded.
veliger = shelled larva of marine gastropod or bivalve mollusc which swims by beating cilia of a velum (bilobed flap).
velum = bilobed flap on veliger larva, with beating cilia for swimming.