Click on photo to enlarge. Scale line in photo equals 1cm unless otherwise specified.
* Species which are commonly encountered on the beach.
San Juan Islands, WA
photographed in an aquarium
Arago, OR, with commensal worm
Neah Bay, WA, intertidalFissurellidea bimaculata (Dall, 1871)Two-Spot Keyhole Limpet
intertidal to 33m size to 50mm
northern Mexico to southern Alaska
is infrequently seen intertidally. The shell is much smaller than
actual animal. The dead shell can sometimes be found
washed up among rocks. The living animal can be difficult to spot among the sponges and tunicates where it hides.
(previous name - Megatebennus bimaculatus)
Diodora aspera (Rathke, 1833)
Rough Keyhole Limpet *
intertidal to 40m size to 76mm
Nicaragua to northern Alaska
is commonly found intertidally. It is far larger than any of the other
local keyhole limpets. The keyhole is round and large compared to the
other species, which exhibit more of an elongated slit opening. The
shell may be uniformly white in color or striped in black, although the
shell is frequently encrusted with other marine life. The animal often shares its shell with a commensal worm, Arctonoe vittata, which helps act as a defensive mechanism, biting its attacker.
Cranopsis multistriata (Dall, 1914)
intertidal to 91m northern Mexico to northern Alaska size to 20mm
This is not commonly seen intertidally. It has smaller and more closely spaced ribs than C. cucullata. The basal edge is smooth. The interior structure behind the slit forms a semi-circle.
(previous name - Puncturella multistriata)
San Juan Islands, WA
Oak Bay, WA, very low intertidalPuncturella galeata (Gould, 1846)
19 - 137m southern California to
northern Alaska size to 20mm
Normally found only subtidally. It was extremely unusual to find the above specimen
intertidally. This species can look very much like some of the other keyhole limpets.
It can be distinguished by the interior structure behind the slit. It exhibits both a
straight shelf and a semi-circular structure.
Puncturella cooperi Carpenter, 1864
subtidal to ? size to 10mm
southern California to southern Alaska
This is found subtidally and is very rare to see.
The height is nearly equal to the length. The
interior structure behind the slit is straight.
This page last revised: 2-7-2016
Comparison of similar species
Scelidotoma bella (Gabb, 1865)
subtidal, 10 to at least 50m size to 75mm
southern California to Ketchikan, Alaska
is only found subtidally and then very rarely. It has
regular radial ribs and a small slit on the anterior side. The
apex curves toward the posterior.
(previous names - Hemitoma bella)
Whiskey Creek Beach, WA
Anacortes, WA, intertidal