Limpet Characteristics

The table below contains information on the typical form of each species. Species are arranged according to intertidal zone from high to low. Variants of several species occur in specialized microhabitats, which are treated separately below. Limpets are highly variable, so expect to find specimens that do not conform neatly to the characters listed here. See references for further detailed discussion.

In the table below: size measurement is maximum length; apex of the shell is located at the indicated proportion of shell length from the anterior end; profile refers to the lateral silhouette (height relative to length); anterior slope (viewed from the side) is convex if it bulges outward, concave if it is dished; interior of the shell is divided into the margin, intermediate area, and central area as indicated at right.

Species	Shell shape & apex (fraction from front)	Shell Sculpture	Shell Margin	Shell Exterior Color/Pattern	Shell Interior Color/Patterns	Side of Foot	Head & Tentacles	Habitat
Lottia gigantea	aperture oval, 90 mm, apex <.10, profile low, anterior slope concave to straight	broad rounded ribs or eroded smooth	slightly wavy	brown w. white checkering or radiating rays	margin & intermediate black to brown, central w. owl-shape outlined by muscle scar	solid black	solid black	high to mid zone, wave-swept areas; also on mussels
Lottia digitalis (rock form) (other forms)	aperture oval, 30 mm, apex <.20, profile medium, anterior slope concave	posterior radial ribs, round in x-sec; interspaces ~convex & not dark	posterior scalloped, anterior smooth	brown to olive w. white chevrons or checkered markings	margin brown & white, intermediate white, central irregular dk. brown	white	white	high to mid zone (esp. vert. faces); also others
Lottia austrodigitalis (rock form) (other forms)	aperture oval, 30 mm, apex <.20, profile medium, anterior slope convex	posterior radial ribs indistinct or square in x-sec, sometimes beaded; interspaces flat	posterior sometimes scalloped, anterior smooth	brown to olive w. white chevrons or checkered markings	margin brown & white, intermediate white, central irregular dk. brown	white	white	high to mid zone, (esp. vert. faces); also others
Lottia scabra	aperture oval, 35 mm, apex <.25, profile medium to low, anterior slope straight	radial ribs all around, triangular in x-sec, interspaces dark	scalloped all around	white to brown w. checkered markings	margin & intermediate white, central w. dull white callus & irreg. brown lines or spots	pale with dark speckles	dorsal side of head w. dk speckles	high to mid zone, on rocks (horizontal)
Lottia paradigitalis ¹	aperture oval, 20 mm, apex .30, profile med., anterior slope straight to concave	fine concentric growth lines; sometimes fine radial riblets	smooth	gray-green w. white speckles or w. white rays bifurcating at margin; apex white	margin narrow; rest of interior white (no pigmented central area)	white	white	high-mid zone interface; also mussel shells
Species	Shell shape & apex (fraction from front)	Shell Sculpture	Shell Margin	Shell Exterior Color/Pattern	Shell Interior Color/Patterns	Side of Foot	Head & Tentacles	Habitat
Lottia persona	oval, 50 mm, apex central (overhangs), profile medium-high, anterior slope straight or concave	fine regular riblets	smooth	dark green-black w. fine white checkering, apex erodes to brown	margin narrow solid dk. brown, intermediate white, central irreg. brown	white	white	high to mid zones, shaded sites; nocturnal
Lottia pelta (rock form)	aperture narrows at front, 40 mm, apex .30, profile medium- high, slope convex all around	broad ribs, often knobby; shell sometimes smooth or eroded	shallow scalloping or smooth	brown, green, black background w. checkered or peripheral bands/rays of white	margin narrow, solid brown or banded; intermediate white, central area irreg. dk. brown or white	white	white	upper mid to low zones; also others
Lottia limatula	aperture oval, 45 mm, apex <.30, profile low to medium, anterior slope straight or convex	radiating radial ribs each w. fine scales (rough to touch)	fine saw-tooth edge	yellow to green-brown, dark mottling / checkered white angular spots	margin narrow solid white or banded brown, intermediate white, central white w. irreg. brown	solid black or broad black lines	dorsal side of head black	mid to low zones
Lottia scutum	aperture wide oval, 60 mm, apex .30 & rounded, profile low to medium, anterior slope convex	smooth or with fine radiating riblets	smooth	brown or green with white spots or lines, highly variable	margin brown or banded, intermediate white w. brown streaks, central irreg. dk. brown	white	tentacles golden brown	mid to low zones
Lottia fenestrata	aperture nearly circular, 30 mm, apex .30, profile medium, anterior slope straight	fine concentric lines; apex often eroded to brown w. lighter area around it	smooth	gray or brown w. fine white speckles or gray w. radial white markings	margin dark, intermediate white suffused w. brown; central dk. brown.; muscle scar evident	white	white	mid to low zones; bare rock in sand or mud
Species	Shell shape & apex (fraction from front)	Shell Sculpture	Shell Margin	Shell Exterior Color/Pattern	Shell Interior Color/Patterns	Side of Foot	Head & Tentacles	Habitat
Lottia instabilis (kelp form) (other forms)	aperture oblong, 30 mm, apex .30, profile high, anterior slope convex; sides parallel	smooth; faint radial ribbing at margin	smooth, curves up at front & back	red-brown to yellow (varies w. habitat)	margin & intermediate bluish-white; central irreg. brown	white	white	low zone, on stipes of kelp
Lottia asmi (turban snail form)	aperture oval-round, 10 mm, apex .50, profile high, anterior slope straight	smooth; faint radial riblets at margin	smooth	black to gray-black	all gray-black	white	white	mid to low zone, shells of turban snails, mussels
Discurria incessa (Egregia form)	elongate oval, 20 mm, apex .30, profile high, anterior slope straight, sides parallel	smooth; fine radial riblets & concentric growth lines	smooth	dark brown w. darker apex	all dark brown	white	dorsal mantle edge darkly pigmented	low zone, on feather boa kelp Egregia
"Lottia" paleacea	aperture oblong, 10 mm, apex .25, profile high, anterior slope concave, sides parallel	very fine rounded radial ribs	smooth	yellowish to dk. brown	margin & intermed. white; central area w. brown spot	white	white	low zone; on blades of surf grass
Acmaea mitra	aperture round, 30 mm, apex subcentral, profile high; anterior slope convex	smooth	smooth	shell white but often covered w. encrusting pink coralline algae	all white	white	white	low intertidal to subtidal, on encrusting corallines

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Specialized Habitats & the Limpets That Live There. | back to top |

Limpet	Gooseneck Barnacles	Mussels	Turban Snails	kelp stipes	Egregia	corallines
Lottia gigantea		X
Lottia digitalis	X	X
Lottia austrodigitalis	X	X
Lottia paradigitalis		X
Lottia pelta	X	X	X	X	X	X
Lottia asmi		X	X
Discurria incessa					X
Lottia instabilis			X	X		X

On Gooseneck Barnacles: Lottia digitalis, L. austrodigitalis Small individuals (<10 mm) of both species live on opercular plates of gooseneck barnacles, Pollicipes polymerus. Shell profiles resemble rock forms, but lack ridges or ribs. Shell color is white or buff with irregular dark brown-black chevrons, which provides excellent camouflage. Species are virtually indistinguishable without molecular sequence data. \| back to table \|
On Mussels: Lottia pelta, L. digitalis, L. austrodigitalis, L. paradigitalis, L. asmi, L. gigantea Lottia pelta on mussels is small (5-25 mm), mostly solid gray to blue-black (much like a mussel shell), with tip of apex near front third of shell (very tip often white with narrow dark brown area around it), a moderate-to-high shell profile, straight anterior slope, and with very fine radial riblets instead of strong radial ridges of its rock form. The interior of the shell is the same as for the rock form. L. digitalis, L. austrodigitalis, and L. paradigitalis on mussels are <10 mm, usually dark but with white radial markings around margins of larger individuals (these are absent on L. pelta). Apex farther forward than L. pelta or L. asmi. Shell surface rough & lacks radial sculpturing. Distinguishing among these 3 in the field is difficult (see interior characteristics, above). L. asmi is usually <8 mm, has a centrally-located apex & a tall profile much as L. pelta. Interior of its shell is black rather than white with a brown central area as in L. pelta. L. gigantea on mussels is <25 mm, narrower, dark gray to black with concentric growth lines; side of foot & head black. \| back to table \|
On Turban Snails: Lottia asmi, L. pelta, L. instabilis, Garnotia adundunca Lottia asmi is small (10 mm), gray-black with a subcentral apex and tall profile. L. pelta here is similar to its mussel form in shape, size, & color. In some locations, L. pelta may be more common on turban snail shells than Lottia asmi which is typically considered to be the "turban snail limpet." L. pelta can be distinguished from L. asmi by its somewhat lower shell profile and a white interior of its shell (compared to gray-black for L. asmi). Lottia instabilis is small, tan to red-brown with white markings; sides of shell parallel. Garnotia adunca is not a true limpet but can be the most abundant hitchhiker on snails shell, especially lower on the shore & subtidally. It can be distinguished from the others by the distinct posteriorly directed hook of its apex. \| back to table \|
On Egregia: Discurria incessa, L. pelta Both species live on the broad flat stipes of the feather boa kelp, Egregia menziesii. Discurria incessa is elongate (20 mm) w. ~parallel sides, dark brown with a darker apex near front third of shell, a high shell profile & a straight anterior slope. L. pelta is small (5-15 mm), brown with white triangular markings, apex near front third of shell and a lower profile than its rock form; anterior slope tends to be concave, shell narrows at anterior, has fine radial riblets & concentric lines but no large radiating ridges. Apex of L. incessa is somewhat taller than L. pelta, its anterior slope is straighter, and the sides of its shell are more parallel than L. pelta. The most dependable shell character is the color of the interior: L. pelta is blue-white with an irregular brown spot in the central area; L. incessa is brown throughout. \| back to table \|
On Kelp Stipes: Lottia instabilis, L. pelta When living on round stipes of Laminaria & other low-shore kelps, shells of both species grow to fit the circumference of the alga, giving the aperture a saddle shape. Except for shape of aperture, L. pelta is similar to its Egregia form in size, shape and color. Lottia instabilis tends to be larger (~20 mm), shell tan to reddish-brown with white markings, parallel sides, and a higher profile than L. pelta; sculpturing is fine evenly-spaced incised radial grooves. Interior color patterns of both spp. similar. \| back to table \|
On Corallines: Lottia instabilis, L. pelta Lottia instabilis (formerly L. ochracea) here is elongate-oval to 30 mm, checkered w. oval white spots over brown or solid yellowish, buff to red-brown; low to medium profile, anterior slope concave; shell with threadlike radial riblets. Recent molecular evidence indicates the coralline form of L. pelta is a new undescribed species rather than a variant. \| back to table \|

References
Lindberg, D.R. 2007. Patellogastropoda. Pages 753-761 in J.T. Carlton, ed. The Light & Smith manual: intertidal invertebrates from Oregon to central California. Univ. Calif. Press, Berkeley, CA [ the most up to date summary of limpet name changes & taxonomic status ]

Other references but with older species names include:
Morris, R.H., D.P. Abbott, & E.C. Haderlie. 1980. Intertidal invertebrates of California. Stanford Univ. Press, Stanford. CA
Lindberg, D.R. 1981. Invertebrates of the San Francisco Bay estuary system: Acmaeidae. Boxwood Press, Pacific Grove, CA

¹Simison, W.B. and D.R. Lindberg. 2003. On the identity of Lottia strigatella (Carpenter, 1864) (Patellogastropoda: Lottiidae). Veliger 46:1-19.
[ documents that L. paradigitalis (northern) & L. strigatella (southern) are separate species. ]

Page created by J.M. Watanabe
All images copyright James Watanabe unless otherwise indicated
Contact: watanabe_at_stanford_dot_edu Last update: 13 June 2018

On Gooseneck Barnacles: Lottia digitalis, L. austrodigitalis Small individuals (<10 mm) of both species live on opercular plates of gooseneck barnacles, Pollicipes polymerus. Shell profiles resemble rock forms, but lack ridges or ribs. Shell color is white or buff with irregular dark brown-black chevrons, which provides excellent camouflage. Species are virtually indistinguishable without molecular sequence data. \| back to table \|
On Mussels: Lottia pelta, L. digitalis, L. austrodigitalis, L. paradigitalis, L. asmi, L. gigantea Lottia pelta on mussels is small (5-25 mm), mostly solid gray to blue-black (much like a mussel shell), with tip of apex near front third of shell (very tip often white with narrow dark brown area around it), a moderate-to-high shell profile, straight anterior slope, and with very fine radial riblets instead of strong radial ridges of its rock form. The interior of the shell is the same as for the rock form. L. digitalis, L. austrodigitalis, and L. paradigitalis on mussels are <10 mm, usually dark but with white radial markings around margins of larger individuals (these are absent on L. pelta). Apex farther forward than L. pelta or L. asmi. Shell surface rough & lacks radial sculpturing. Distinguishing among these 3 in the field is difficult (see interior characteristics, above). L. asmi is usually <8 mm, has a centrally-located apex & a tall profile much as L. pelta. Interior of its shell is black rather than white with a brown central area as in L. pelta. L. gigantea on mussels is <25 mm, narrower, dark gray to black with concentric growth lines; side of foot & head black. \| back to table \|
On Turban Snails: Lottia asmi, L. pelta, L. instabilis, Garnotia adundunca Lottia asmi is small (10 mm), gray-black with a subcentral apex and tall profile. L. pelta here is similar to its mussel form in shape, size, & color. In some locations, L. pelta may be more common on turban snail shells than Lottia asmi which is typically considered to be the "turban snail limpet." L. pelta can be distinguished from L. asmi by its somewhat lower shell profile and a white interior of its shell (compared to gray-black for L. asmi). Lottia instabilis is small, tan to red-brown with white markings; sides of shell parallel. Garnotia adunca is not a true limpet but can be the most abundant hitchhiker on snails shell, especially lower on the shore & subtidally. It can be distinguished from the others by the distinct posteriorly directed hook of its apex. \| back to table \|
On Egregia: Discurria incessa, L. pelta Both species live on the broad flat stipes of the feather boa kelp, Egregia menziesii. Discurria incessa is elongate (20 mm) w. ~parallel sides, dark brown with a darker apex near front third of shell, a high shell profile & a straight anterior slope. L. pelta is small (5-15 mm), brown with white triangular markings, apex near front third of shell and a lower profile than its rock form; anterior slope tends to be concave, shell narrows at anterior, has fine radial riblets & concentric lines but no large radiating ridges. Apex of L. incessa is somewhat taller than L. pelta, its anterior slope is straighter, and the sides of its shell are more parallel than L. pelta. The most dependable shell character is the color of the interior: L. pelta is blue-white with an irregular brown spot in the central area; L. incessa is brown throughout. \| back to table \|
On Kelp Stipes: Lottia instabilis, L. pelta When living on round stipes of Laminaria & other low-shore kelps, shells of both species grow to fit the circumference of the alga, giving the aperture a saddle shape. Except for shape of aperture, L. pelta is similar to its Egregia form in size, shape and color. Lottia instabilis tends to be larger (~20 mm), shell tan to reddish-brown with white markings, parallel sides, and a higher profile than L. pelta; sculpturing is fine evenly-spaced incised radial grooves. Interior color patterns of both spp. similar. \| back to table \|
On Corallines: Lottia instabilis, L. pelta Lottia instabilis (formerly L. ochracea) here is elongate-oval to 30 mm, checkered w. oval white spots over brown or solid yellowish, buff to red-brown; low to medium profile, anterior slope concave; shell with threadlike radial riblets. Recent molecular evidence indicates the coralline form of L. pelta is a new undescribed species rather than a variant. \| back to table \|