|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.
|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).
|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.
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.
form of Lottia pelta
Recent molecular evidence indicates this form is a new undescribed species rather than a variant form of L. pelta.