Black Limpet, Volcano Limpet
Phylum: Mollusca, Class: Gastropoda, Order: Lepetellida, Family: Fissurellidae, Genus: Fissurella, Species: volcano · Fissurellidae (Keyhole Limpet family) · Gastropod (univalve); whole shell; conical/tent-shaped with an apical opening (keyhole).
Species
Fissurella volcano (Confidence level: 90%)
Shell Type
Gastropod (univalve); whole shell; conical/tent-shaped with an apical opening (keyhole).
Family
Fissurellidae (Keyhole Limpet family)
Size
Approximately 0.75 to 1.25 inches (20-30mm). This is a standard adult size for the species, which typically caps at about 40mm.
Color & Pattern
External coloration features a base of grayish-white with distinct dark brown or burgundy-purple radial streaks and ribs. The apex is worn to a lighter tone. Internal surface is usually smooth and milky white with a polished appearance around the central 'keyhole'.
Rarity
Common; frequently found on rocky shorelines and washed up on beaches in the Cabo and Baja regions.
Habitat
Found in the intertidal zone, specifically adhering to rocks in areas with high wave energy. They are marine gastropods that prefer rocky substrates where they can graze on algae.
Geographic Range
Eastern Pacific coastline, ranging from Northern California (Bodega Bay) down to Baja California (Cabo San Lucas) and the Gulf of California.
Description
A sturdy, volcano-shaped shell with a small, elongated oval opening at the peak. The exterior is heavily sculpted with numerous fine radial ribs that extend from the apex to the margin. The margin is slightly crenulated due to the ribs. It has a low-profile, aerodynamic shape designed to withstand heavy surf.
Key Features
The most diagnostic feature is the 'keyhole' (apical pore) at the summit, which functions for waste expulsion and respiration. The volcano-like profile and radiating dark purple-brown stripes provide the specific ID.
Collector Value
Minimal monetary value (typically $1-$5 USD) due to its commonality, but highly desirable for regional biodiversity collections and educational sets because of its unique morphology.
Condition Notes
The specimen shows some minor erosion on the radial ribs and apex, likely from natural wave action. Color remains vibrant. Condition Grade: Good to Fine, typical for a beach-collected specimen.
Interesting Facts
Unlike most snails, keyhole limpets have two gills. The 'keyhole' allows water to flow in under the shell edge and exit through the top, carrying away metabolic waste. They have a strong homing instinct, often returning to the exact same 'scar' or spot on a rock after feeding.
Ecological Role
Primary consumer/herbivore; they graze on microfilm algae, helping to maintain the balance of the rocky intertidal ecosystem. They serve as a food source for crabs, sea stars, and shorebirds.
Similar Species
Fissurella nigrocincta (smaller, different banding) and Lucapina sowerbii (fleshy mantle covers more of the shell). Distinguishable by the Volcano Limpet's specific radial staining and size.
Beach Finding Tips
Search during low tide among tide pools and rocky outcrops. They are often found in the drift line near rocky headlands. Look for small 'volcano' shapes amongst shell hash.
Notes
Cabo