Keyhole Limpet (Panamic Keyhole Limpet)
Phylum: Mollusca, Class: Gastropoda, Order: Lepetellida, Family: Fissurellidae, Genus: Fissurella, Species: Fissurella microtrema · Fissurellidae (Keyhole Limpet family) · Gastropod (univalve); Cap-shaped/Conical shell with a natural apical perforation (hole) at the top.
Species
Fissurella microtrema (90% confidence based on Cabo location and radiating ribs)
Shell Type
Gastropod (univalve); Cap-shaped/Conical shell with a natural apical perforation (hole) at the top.
Family
Fissurellidae (Keyhole Limpet family)
Size
Approximately 15-20mm in length. This is a small specimen; adults of this species typically range from 15mm to 35mm.
Color & Pattern
Cream to light tan base color with hints of brownish-orange radiating streaks. The interior appears white or grayish with a faint muscle scar. The colors are somewhat weathered but retain natural pigmentation.
Rarity
Common beach find in the Cabo region, though intact specimens with sharp sculpture are less common due to the high wave action of the Southern Baja coastline.
Habitat
Found in the intertidal and shallow subtidal zones, typically clinging to the underside of rocks or in crevices in high-energy rocky reef environments.
Geographic Range
Panamic Province: Eastern Pacific from the Gulf of California (including Cabo San Lucas) south to Peru.
Description
A small, low conical shell with a characteristic 'keyhole' opening at the apex. The surface is sculpted with fine, numerous radiating ribs and concentric growth lines that create a slightly beaded or roughened texture. The margin (edge) is slightly crenulated or scalloped following the rib pattern.
Key Features
The most diagnostic feature is the oval apical hole which serves as an exit for water and waste. The low profile and the specific radiating rib structure help identify it as a member of the Fissurella genus.
Collector Value
Low monetary value ($1-$5) due to its abundance and worn condition. However, it is a classic 'representative' specimen for any regional Cabo collection or educational display.
Condition Notes
Fair to Good. There is significant beach-worn erosion on the ribs and edges. The apical hole is slightly chipped and the colors are somewhat faded by sun exposure and sand abrasion. Collectibility grade: Fair.
Interesting Facts
Unlike 'true' limpets, keyhole limpets have a hole that acts as a chimney for their waste. They have a strong muscular foot that allows them to suction onto rocks so tightly they can withstand heavy Pacific surf. In some cultures, larger species are used for food.
Ecological Role
They are grazers that scrape algae and detritus from rock surfaces using a specialized tongue-like organ called a radula, helping to clear space for other organisms on the reef.
Similar Species
Fissurella rugosa (more coarsely ribbed) and Diodora inequalis (the hole is positioned more toward the front rather than central apex).
Beach Finding Tips
Search the rocky tide pools at low tide around areas like Playa Chileno or the rocky outcrops near the Arch. Look for small, stone-like bumps on the undersides of loose rocks.
Notes
Cabo