Limpets - cap-shaped snails

Lottia gigantea Sowerby, 1834
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Owl limpet; apex near front, height low, anterior slope concave; 90 mm long, brown & white markings but often  eroded; side of foot gray, sole orange or yellow. Small form lives on mussels, somewhat more elongate, <25 mm & dark blue-black w. concentric growth lines. Side of foot & head solid black.

Common, especially on vertical faces in wave-swept areas; high & mid-intertidal; territorial browser on algal films; grows slowly & may live for decades.

Geogr. Range: Washington to Baja
Synonyms:
Similar species: see table

Image: on owl limpet's back L. scabra  (2 at rt.); gooseneck barnacle form of L. digitalis or L. austrodigitalis at left.

Lottia digitalis (Rathke, 1833)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Apex near front, sometimes overhangs; height moderate, anterior slope concave; to 30 mm long; may have radial ribs (round x-sec) on posterior but not anterior; brown to dark olive w. white checkering; shell characters highly variable.

Northern species. Abundant, high to mid-intertidal zones, exposed & protected outer coast; in Monterey occurs more frequently on Pollicipes than on rock; also on mussels shells.

Geogr. Range: Aleutian Islands, Alaska to Pt. Conception
Synonyms: Collisella digitalis, Acmaea digitalis
Similar species: L. austrodigitalis is nearly identical; see table

Lottia austrodigitalis (Murphy, 1978)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Apex near front, height moderate, anterior slope concave; to 30 mm long; radial ribs not pronounced on posterior (when present, square in x-sec, often beaded); brown to olive w. white checkering; shell highly variable.

Southern species. Abundant, on rock (in Monterey), high to mid-intertidal zones; exposed & protected outer coast; also on plates of Pollicipes & on mussel shells.

Geogr. Range: Pt. Conception to northern Baja; southern Monterey Bay
Synonyms: Collisella austrodigitalis
Similar species: L. digitalis is nearly identical but in Monterey its goose barnacle form is more frequent; see table

Image: mostly L. austrodigitalis; possible L. digitalis just left of center facing downward.

Lottia scabra (Gould, 1846)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Conspicuous radial ribs (triangular x-sec) with darker- pigmented interspaces & margin scalloped all around; to 35 mm long; side of foot & head white with black speckles; apex at front quarter of shell; height low to moderate, anterior slope straight; shell mottled tan, gray, white.

Abundant, high to upper mid-intertidal zone on horizontal surfaces, exposed & protected outer coast. Homes to specific site at low tide; also lives on Lottia gigantea.

Geogr. Range: Cape Arago, OR to southern Baja
Synonyms: Collisella scabra, Macckintockia scabra, Acmaea scabra
Similar species: L. digitalis & L. austrodigitalis lack black speckles on side of foot & anterior ribs on shell; see table.

Lottia paradigitalis (Fritchman, 1960)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Small limpet to 20 mm long; fine concentric lines, rarely with radial riblets; apex at front third of shell & often eroded white; height moderate; anterior slope straight;  gray-green with white speckling or blue-gray with white rays bifurcating at margin, but color highly variable; interior all white.

Common, on rocks, top of mid intertidal zone, exposed to protected outer coast.

Geogr. Range: Alaska to Pt. Conception
Synonyms: Collisella paradigitalis  (C. borealis & L. strigitella were formerly considered the same spp., but all are now sep. spp.)
Similar species: see table; L. digitalis & L. austrodigitalis have dark brown central areas on interior of shell.

Lottia pelta (Rathke, 1833)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Shield limpet; shell narrows toward anterior end; apex at front third to sub-central, height moderate to tall; anterior slope convex; to 45 mm long; shallow ribs (oft. eroded) or smooth; color highly variable: brown, green, to black with white checkering or peripheral rays (see notes).  

Abundant, high to low intertidal zones, exposed to protected outer coast. 4-5 dif. forms (rock, mussel, kelp, turban snail, coralline) which are probably dif. spp..

Geogr. Range: Aleutian Islands, Alaska to Baja
Synonyms: Collisella pelta, Acmaea pelta
Similar species: see table

Lottia persona (Rathke, 1833)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Large (to 50 mm), moderately tall; dark olive-green with fine white speckles; apex at front third of shell sometimes overhanging & eroded dark brown; height moderate; anterior slope straight to concave; fine radial riblets (often eroded).

Common, but cryptic; high to mid-intertidal zones, protected outer coast; in crevices, caves, under overhangs; nocturnal.

Geogr. Range: Alaska to Morro Bay, central Calif.
Synonyms: Notoacmaea persona, Tectura persona, Acmaea persona
Similar species: see table; L. pelta has similar profile, but has obvious ridges & different color pattern.

Lottia limatula (Carpenter, 1864)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

File limpet; side of foot & head black (unlike any other local limpet); shell to 45 mm long with distinctive fine scaly radiating ribs (often eroded) & finely serrate margin; apex at front third of shell, height low to moderate, anterior slope straight; shell yellow, white, greenish, with dk. mottling or white spots; .

Abundant, mid to low intertidal zones, protected outer coast.

Geogr. Range: central Oregon to southern Baja
Synonyms: Collisella limatula,  Acmaea limatula
Similar species: no other limpet has rough scaly radiating ribs on shell and black side of foot; see table

Lottia scutum (Rathke, 1833)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Plate limpet; head with golden tentacles; shell flat, broad to 60 mm long; smooth or with fine radiating riblets; apex at front third of shell, height low; anterior slope convex; color varies from tan, brown to gray-green; with checkered white spots or rays.

Abundant, mid to low intertidal zones, exposed & protected outer coast.

Geogr. Range: Bering Sea to Pt. Conception
Synonyms: Notoacmaea scutum, Acmaea scutum
Similar species: no other limpet has golden brown cephalic tentacles; see table.

Lottia fenestrata (Reeve, 1855)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Nearly circular to 30 mm long with fine concentric lines; apex at front third of shell, height moderate; anterior slope straight; gray, brown with fine white speckles or radial white markings; apex often brown with adjacent area lighter; interior bluish-white suffused with brown & dark central area.

Moderately common, on bare rock embedded in sand, mid to low intertidal zones, protected outer coast.

Geogr. Range: Alaska to Baja
Synonyms: Notoacmaea fenestrata, Acmaea fenestrata
Similar species: see table

Acmaea mitra Rathke, 1833
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Acmaeidae

Apex central, height tall (30 mm), anterior slope convex; lacks radial sculpture; to 35 mm long; white but often encrusted with coralline algae.

Common, on rocks with encrusting and erect coralline algae; low intertidal zone to subtidal; exposed & protected outer coast; browses on coralline algae.

Geogr. Range: Aleutian Islands, Alaska to Baja
Synonyms:
Similar species:  see table

Lottia asmi (Middendorf, 1847)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Apex at front third of shell to subcentral, height tall (.5x length), 10 mm long, anterior slope straight; exterior with very fine riblets, black to dark gray-brown; interior dark brown.

Lives most often on shells of turban snails, mussels, or goose barnacles; also on rock (flatter profile); mid to low intertidal zones, protected outer coast.

Geogr. Range: British Columbia to Baja
Synonyms: Collisella asmi, Acmaea asmi
Similar species: L. pelta & L. paradigitalis also occur on shells; see table

Discurria incessa (Hinds, 1842)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Narrow tall shell with ~parallel sides; apex at front third of shell, height tall, to 20 mm long, anterior slope straight; very fine riblets & concentric lines; color glossy brown. Dorsal mantle margin is dark.

Lives on stipes of Egregia menziesii, low intertidal zone exposed & protected outer coast

Geogr. Range: Alaska to central Baja
Synonyms: Discurria incessa, Acmaea incessa
Similar species: L. pelta also occurs on Egregia & looks similar; see table

Lottia instabilis (Gould, 1846)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Highly variable; apex at front third of shell, height tall; to 35 mm long, anterior slope convex; threadlike radial riblets, solid color (red-brown, yellowish, tan) or checkered oval white spots.

Lives on stipes of kelp, rock, corallines, or shells; low intertidal zone; 5 variants; kelp form has parallel sides raised at front & back so it rocks on flat surface. Form common on intertidal Chlorostoma funebralis has lower apex.

Geogr. Range: Aleutian Islands, Alaska to San Diego
Synonyms: Collisella ochracea, C. instabilis
Similar species: see table

"Lottia" paleacea (Gould, 1853)
Phylum Mollusca, Class Gastropoda, Subcl. Patellogastropoda, Family Lottidae

Shell oblong (3-4x longer than wide) to 10 mm long, height tall; anterior slope concave, sides of shell parallel; fine rounded radial ribs; yellowish to dk. brown.

On blades of surf grass; low intertidal zone, exposed & protected outer coast.  Molecular data indicate this spp. is more closely related to tropical lottiids than local temperate forms & probably belongs in another genus besides Lottia. 

Geogr. Range: Aleutian Islands, Alaska to San Diego
Synonyms: Notoacmaea paleacea, Tectura paleacea
Similar species: see table