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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.  
table

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

Lottia 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

 

 

 

Lottia 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.  
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On Mussels:  Lottia pelta, L. digitalis, L. austrodigitalis, L. paradigitalis, L. asmi, L. gigantea     
L. 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.
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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.
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On EgregiaLottia incessa, L. pelta   
Both species live on the broad flat stipes of the feather boa kelp, Egregia menziesii.
     L. 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.
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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.  
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On Corallines:  Lottia instabilis, L. pelta   
L. 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.
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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

1 Simison, 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: 8 October 2009