Length 8.6 mm when live. Eight overlapping, thin, fragile, white or cream valves stained with black manganese and rust coloured ferrous deposits.
1: No lateral insertion plates or slits.
2: Tegmentum layer eroded from central area of head valve on this old specimen, exposing underlying ungranulated articulamentum layer.
Articulamentum projects beyond tegmentum as apophyses to underlie next valve, triangular on intermediate valves (3), but rounded trapezoidal on tail valve viii (4).
Llŷn, North Wales. March 2016.

KEY ID FEATURES BELOW

Key identification features
Leptochiton cancellatus
1: Small; maximum length 9mm. Valves whitish or cream, often stained in patches or streaks with black manganese and/or rust coloured ferrous deposits. No lateral insertion plates or slits. a 02 Leptochiton cancellatus
2: Only at LWS and sublittorally. All round Britain. Probably overlooked.
3: Narrow whitish girdle has no pattern, may be stained with rust coloured ferrous, and/or blackish manganese, deposits. Dorsal girdle scales squarish with rolled tip. a 09 Leptochiton cancellatus .
4: Arch of valves is moderately high smooth curve with no sign of a keel. Elevation of arch valves iv & v; height/width 39% (Kaas&Belle), but illustrated specimen 46%. a 05 Leptochiton cancellatus .
5: No posterior beak on intermediate valves. a 04 Leptochiton cancellatus .
6: Cancellated by closely packed, almost touching, oval granules in chainlike lines running radially on valves i & viii, and on lateral areas of valves ii to vii (sometimes obsolete on lateral areas) . Lines Longitudinal on central areas of valves ii to vii. a 09 Leptochiton cancellatus .
7: Sole whitish pink centrally, becoming reddish pink towards periphery. a 10 Leptochiton cancellatus .
8: Ctenidia close to anus at posterior (merobranch) a 10 Leptochiton cancellatus .
9: Tail valve shorter than on L. sarsi; length 45% of width in life position ( 51% on illustrated specimen) a 06 Leptochiton cancellatus .
10: Mucro slightly swollen and to posterior of centre of extracted valve viii (part of anterior concealed on live specimens) a 06 Leptochiton cancellatus . Postmucronal slope entirely concave a 07 Leptochiton cancellatus .

Similar species
*or ** indicate principal distinguishing features.
Lepidochitona cinerea (Linnaeus, 1767). flic.kr/s/aHsk7KqLr3
1*: Maximum length 28mm. Valves diversly coloured and patterned, including whitish resembling Leptochiton cancellatus a 12 Leptochiton cancellatus album COMPARISON Lepidochitona cinerea. . Lateral insertion plates separated by single slit on each end of valves ii to vii.
2: Midshore level and below. All round Britain. Commonest littoral chiton.
3**: Girdle has a unique (in N.W. Europe) lozenge pattern a 13 Leptochiton cancellatus album COMPARISON Lepidochitona cinerea. , but sometimes indistinct, especially on whitish specimens which are easily confused with Leptochiton cancellatus a 14 Leptochiton cancellatus album COMPARISON Lepidochitona cinerea .
4*: Arch of valves is keeled a 15 Leptochiton cancellatus album. COMPARISON L. scabridus & Lepidochitona cinerea. .
5*: Distinct posterior beak on intermediate valves a 12 Leptochiton cancellatus album COMPARISON Lepidochitona cinerea. .
6: Dorsal surface of valves has densely packed rounded granules, not in straight lines.
7: Sole pinkish white to orange pink, usually with grey viscera showing centrally.
8*: Usually 16 to19 ctenidia each side for whole length of foot (holobranch).

Leptochiton asellus (Gmelin, 1791)
1*: Maximum size 18mm X 10mm. Valves whitish, sometimes with distinct black longitudinal lines a 16 Leptochiton cancellatus album COMPARISON L. asellus. or general staining by black or rust coloured mineral deposits a 17 Leptochiton cancellatus album COMPARISON L. asellus. . . No lateral insertion plates or slits.
2: Only at LWS and sublittorally. All round Britain, probably commonest sublittoral chiton.
3: Whitish girdle has no pattern, may be stained with rust coloured ferrous, and/or blackish manganese, deposits. Dorsal girdle scales elongate, bluntly pointed a 18 Leptochiton cancellatus album COMPARISON L. asellus. .
4**: Arch of valves is quite high with distinct keel* and straight* side slopes a 18 Leptochiton cancellatus album COMPARISON L. asellus. . (Elevation of arch valves iv & v; height/width 36%)
5: Often a slight beak on intermediate valves, especially valves ii & iii.
6: Roughly oval granules in slightly disjointed lines, oriented as on L. cancellatus
7: Sole whitish pink centrally, becoming reddish pink towards periphery.
8: Eight to thirteen ctenidia in posterior half of pallial groove (merobranch).
9: Tail valve length less than 50% of width in life position.
10: Mucro not swollen and slightly to anterior of centre of valve viii.

Leptochiton scabridus (Jeffreys, 1880).
18.a 18.2 Leptochiton cancellatus album COMPARISON L. scabridus.
1: Small; maximum size 8mm X 4mm. Valves whitish to dull orange, sometimes with staining by black or rust coloured mineral deposits. No lateral insertion plates or slit.
2*: Only at LWS and sublittorally. Rare, only SW England, Channel Islands & Brittany.
3: Narrow whitish girdle has no pattern, may be stained with rust coloured ferrous, and/or blackish manganese, deposits.
4: Arch of valves is a smooth curve with very slight indication of carina, lower in profile than on L. cancellatus.
5: No posterior beak on intermediate valves, but anterior of valve ii tends to be angulated.
6*: Rows of raised, round granules on valves, oriented as on L. cancellatus, but coarser. Compare at nature22.com/estran22/mollusques/polyplacodentale/chitons…
7*: Whole sole strikingly bright red. 18.a 18.1 Leptochiton cancellatus album COMPARISON Leptochiton scabridus
8: Ctenidia confined to posterior half (merobranch).
9: Tail valve length about 55% of width in life position.
10: Mucro swollen and near centre of valve viii. Postmucronal slope entirely concave.

Leptochiton sarsi Kaas, 1981
Very similar and closely related to L. cancellatus. All Scandinavian specimens previously recorded as L. cancellatus that were examined by Kaas (1981) were considered by him to be L. sarsi. No British records on NBN, but one from Guernsey (1922) and others from Mediterranean (Dell’Angelo et al, 2009), so, if these correctly identified, possibilty that L. sarsi may be in British waters unrecognised.
1: Maximum size 10mm X 5mm.
2*: Western Sweden to northern Norway at depths 40m to 700m.
3: Narrow girdle. Dorsal scales elongate, conical.
4: Arch of valves is high and rounded to slightly keeled. Elevation of arch of valves iv & v; height/width 48%.
6*: Valve granules coarser than on L. cancellatus with wider gaps between them. Granule lines not radial on valves i & viii or lateral areas of valves ii to vii. Lines longitudinal on central areas of valves ii to vii; spaced wider than on L. cancellatus so fewer rows (12 rows match width of an apophysis, about 16 on L. cancellatus). a 19 Leptochiton cancellatus album COMPARISON L. sarsi. & a 20 Leptochiton cancellatus album COMPARISON L. sarsi. .
9: Tail valve long, length 60% of width.
10*: Mucro on tail valve viii not swollen and postioned slightly to anterior of centre. Postmucronal slope concave only to immediate posterior of mucro; changes to straight or slightly convex further to posterior a 07 Leptochiton cancellatus .

Leptochiton rugatus Carpenter in Pilsbury, 1892
All Pacific specimens previously recorded as L. cancellatus that were examined by Ferreira (1979) were considered by him to be L. rugatus. It has a quite different radula.