Biology/Natural History: Species is omnivorius but prefers encrusting bryozoans. Extends its mantle extremely when it encounters a seastar predator (such as Pycnopidia, Leptasterias, Pisaster, or Orthasterias) so that the shell is largely covered and the seastar has no place to grab onto the shell. Often contains a symbiotic polychaete worm Arctonoe vittata (picture) in its mantle cavity which may bite the seastar as well. Diodora's blood contains hemocyanin, has a low pH (7.1) and no Bohr effect.

Shell is caplike, like a limpet and up to 7 cm long. The apex of the shell has a round or broadly oval anal opening which is about 1/10 the length of the shell. Animal's mantle, when the animal is alive, covers only the very margin of the shell if at all (shell is nearly entirely exposed). Shell is often gray or gray-brown and sculptured with coarse radial ribs (picture), may have black and white radiating stripes (picture).

The Rough Keyhole Limpet can be found anywhere in coastal regions from Afognak, Alaska, to Baja Calafornia. It is found primarily in low intertidal areas, and has been seen up to 40 feet subtidally in the south (Morris et al. 1980).

Biogeographic Regions: pacific ocean (Native )

Geographical Range: Afognak Island, Alaska to Camalu, Baja California.

This gastropod has a unique and diagnostic hole in the apex of its shell (about 1/10 the shell length, and slightly anterior to the center) which functions as an exhalant opening. Water is drawn up under the shell from the forward end and over the gills, where it is then forced out of the hole. Because the limpet anus lies near the gills, (a result of the torsion process) this method of respiration is essential in maintaining mantle cavity sanitation, as Diodora aspera is constantly receiving clean, oxygen rich seawater. Other limpets lack this unique flow-through system, but have developed different methods to seperate clean incurrent seawater from waste-laden excurrent flow.

 The Keyhole Limpet can reach lengths of up to 70 mm. Its shell is thick and has a triangular shape in profile. This organism has coarse exterior, with numerous rough radial ribs (every forth rib larger) crossed by concentric threads, creating somewhat of a lattice effect. The shell color is greyish white, with brownish rays radiating from the apex. The interior of Diodora aspera is white and the edge of the shell is crenulate (Morris et al. 1980).

How to Distinguish from Similar Species: In Puncturella and Fissurella species the dorsal hole is an elongated slit. Megathura crenulata (the giant keyhole limpet) lives farther south, grows much larger, and the mantle covers much to all of the shell when the animal is alive.

The Keyhole Limpet clings tenaciously on and under large rocks in the sub to low intertidal. They can also be found on large kelp stipes. Their strong foot allows them to thrive in some intertidal areas where turbulent wave action is prevalent.

Aquatic Biomes: coastal

Known from seamounts and knolls

Depth range based on 47 specimens in 1 taxon.
Water temperature and chemistry ranges based on 41 samples.

Environmental ranges
  Depth range (m): -0.5 - 49.65
  Temperature range (°C): 9.215 - 10.345
  Nitrate (umol/L): 5.634 - 7.622
  Salinity (PPS): 31.235 - 32.111
  Oxygen (ml/l): 6.534 - 6.794
  Phosphate (umol/l): 0.883 - 1.030
  Silicate (umol/l): 12.975 - 20.289

Graphical representation

Depth range (m): -0.5 - 49.65

Temperature range (°C): 9.215 - 10.345

Nitrate (umol/L): 5.634 - 7.622

Salinity (PPS): 31.235 - 32.111

Oxygen (ml/l): 6.534 - 6.794

Phosphate (umol/l): 0.883 - 1.030

Silicate (umol/l): 12.975 - 20.289
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Depth Range: Low intertidal to subtidal

Habitat: Common in rocky areas all along the coast

This particular limpet is an omnivorous grazer. It feeds by scraping rocks with its radula. Various bryozoans are its food of choice, but it also consumes algae, as well as some sponge species (Morton 1958).

Keyhole limpets have seperate sexes, and sexually ripe individuals can be found during any season of the year. Eggs and sperm are released into the water in mass quantities and larval settlement ensues (Sanders 1998).

Adhesion occurs in varying conditions: keyhole limpet
 

The body of keyhole limpets attaches to tidal zone substrates in varying conditions via a dual mode attachment mechanism, using either suction or glue-like adhesion.

       
  "The attachment mechanism used by limpets (Lottia) in the rocky, wave-swept intertidal zone of California was determined during high tide and low tide. The two mechanisms that limpets are known to use, suction and glue-like adhesion, were distinguished by measuring the limpets' attachment forces in shear and by staining for glue-like residues where the limpets had been attached. The results show that approximately equals 73% of limpets at high tide use suction, while the rest use glue-like adhesion. Conversely, approximately equals 75% of limpets at low tide use glue-like adhesion, while the rest use suction. The normal tenacity of limpets was also measured at high and low tide. The mean tenacity at high tide was significantly less than that at low tide. From these data it was estimated that the mean tenacity of glue-like adhesion is approximately equals 0.23 MN/sq m and the mean tenacity of suction adhesion is approximately equals 0.09 MN/sq m. It is hypothesized that the cycle of alternating attachment mechanisms is linked to the limpets foraging cycles." (Smith 1992:205)

"Naturally, nothing precludes an organism from using some combination of adhesive mechanisms; and determining relative contributions can be sticky…limpets use suction mainly when they need mobility, relying on glue rather than continuous muscular effort for longer term attachment (Ellem, Furst, and Zimmerman 2002). They don't, though, use Stefan adhesion (Smith 1992)." (Vogel 2003:429)
  Learn more about this functional adaptation.

Limpets play a key role in the intertidal ecosystems where they thrive. As algeal grazers, they help maintain the delicate and complex balance essential for such a diverse group of organisms to survive. They clear rocks of algae, allowing space for other organisms such as Mytilus (mussel) and Chthalamus (barnacle) species to attach to the substrate. Additionally, they are an important food source for the keystone predator Pisaster Ochraceus (seastar).

The Keyhole limpet has an extremely unique feature associated with its blood. The blue respiratory pigment, hemocyanin, shows no change in its affinity for oxygen when pH levels are altered. In studying this feature, scientists are working to determine how this respiratory pigment differs from our own from a molecular structure standpoint. In this manner, this organism may help provide new information in defining the structure and function of human blood components (Morris et al. 1980).