Lottia pelta, the Shield Limpet                                                                         | main limpet page | limpet table | SeaNet home |

Lottia pelta is one of the most variable and widely distributed of intertidal limpets in Monterey Bay.  There are several variants that live in specific microhabitats (rock, mussels, turban snails, Egregia, other kelps), each with different shell characteristics (an additional coralline form of L. pelta has since been determined to be an undescribed species based on molecular evidence).  Individuals may change microhabitat with age (size), which is accompanied by corresponding changes in color and shell architecture.  Molecular evidence suggests these variants are different enough to be considered separate species.  To complicate matters further, similar morphs of other polytypic species (e.g. Lottia instabilis) co-occur with L. pelta in some of these microhabitats.

Rock form of Lottia pelta
Lottia pelta typically lives on rocky substrate, ranging from the high intertidal where there is little algal cover to very low on the shore.  The rock form has a high shell profile with a subcentral apex and prominent (though often eroded) radial ribs, with or without bumpy nodules.  Shell color varies from light brown to gray-black with various radial white markings. The aperture is usually narrower toward the anterior end.  The interior of the shell has a narrow dark brown margin, sometimes with white marks corresponding to exterior shell colors.  The intermediate area is shiny blue-white almost like porcelain and the central area has an irregular brown stain (which is sometimes absent). The side & sole of the foot and the cephalic tentacles on the head lack pigmentation.  The variety of color patterns and degree of ribbing can be seen in the rock forms below.

Other abundant rock-dwelling mid-shore limpets in Monterey are Lottia limatula and L. scutum.  Lottia pelta can be distinguished from both by its taller profile & radial ribs.  L. limatula is flatter than L. pelta and its radial ribs are finer and have tiny scaly teeth, giving the shell a distinct rough feel.  The side of its foot and top of its head are black while those of L. pelta are white.  L. scutum is flat and usually smooth or with very fine non-scaly radiating riblets.  Its apex is  rounded than L. pelta and more central than that of L. limatula.  The tentacles on its head are golden brown, unlike any other limpet in Monterey.

Higher on the shore, L. scabra also has prominent radiating ribs, but its shell is flatter than L. pelta and its apex closer to the front.  The side of the foot and head of L. scabra have speckles of black pigment (not ~solid black like L. limatula) while those of L. pelta are white.          | back to top |

     A sample of rock-dwelling forms of Lottia pelta
Lottia pelta

Mussel form of Lottia pelta     
The mussel form is smaller (5-25 mm), typically has a moderately high shell profile with the apex near the front third of the shell.  It lacks strong radial ridges of the rock form and instead has very fine radial riblets.  Shell color is brown or gray to blue-black (much like the mussel shells on which it lives) apex often white surrounded by narrow brown area. The aperture narrows slightly toward the anterior end. The interior of the shell is the same as for the rock form.   Other limpets living on mussel shells include Lottia asmi, L. digitalis, L. austrodigitalis, and L. paradigitalis.  Shells of the latter 3 spp. are usually <10 mm, often heavily eroded, and the apex is farther forward than L. pelta.  L. asmi has a somewhat more centrally-located apex & the interior of its shell is black rather than white with a brown central area.
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Turban snail form of Lottia pelta    
Similar to mussel form in shape, size, & color.  In some locations, this form may be more common on turban snail shells than Lottia asmi which is 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).
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Egregia form of Lottia pelta   
Small (5-15 mm) with apex near front third of shell and a lower profile than the rock form.  The anterior slope of the shell tends to be concave, compared to straight or convex for other forms of L. pelta. The shell has fine radial riblets & concentric lines but not large radiating ridges. Shell color brown with white triangular markings. Lottia incessa  also lives on Egregia and is brown.  Its apex is somewhat taller than L. pelta, its anterior slope is straighter, and the sides of its shell are more often 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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Kelp form of Lottia pelta   
Similar to Egregia form in size, shape and color.  When living on round stipes of Laminaria & other low-shore kelps, the shell grows to fit the circumference of the alga, giving the aperture a saddle shape.  Lottia instabils also occurs on low-shore kelps; it tends to be larger (~20 mm), has a higher shell profile & has fine evenly-spaced incised radial grooves.  Interior color patterns are similar in the two spp. making them difficult to distinguish.  
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Coralline form of Lottia pelta   
Recent molecular evidence indicates this form is a new undescribed species rather than a variant  form of L. pelta.
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Page created by J.M. Watanabe
All images copyright James Watanabe unless otherwise indicated

Contact:  watanabe_at_stanford_dot_edu                                                                                                                                   Last  update: 10 October 2009