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).
Other Physical Features: ectothermic ; bilateral symmetry
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
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 )
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).
Recent studies suggest that this animal's unique apical opening is not only associated with sanitation, but also plays an important role in inducing passive flow through the mantle cavity. In studies where the keyhole of Diodora aspera was blocked (either naturally or experimentally) no evidence of damage to the mantle cavity or associated organs was found. In these experimental trials, water entered ventro-posteriorly with respect to the gill tips, and exited over the head region (near the anus). The apical opening proved unnecessary as a means of waste removal. Researchers did find however, that the keyhole played an essential role in allowing water to flow passively through the mantle cavity. Thus, it is thought that this function of the apical opening may have been just as significant as its role in sanitation in terms of limpet evolution (Voltzow et al. 1995).
The polychaete Arctonoe vittata is an extremely common commensal organism found within the mantle cavity of the Keyhole Limpet. The worm, sometimes as long or longer than the limpet itself, often bites predatory seastars that attach themselves to its host, causing them to retreat (Morton 1958).
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).
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).
Diodora aspera, also known as the rough keyhole limpet, is a species of sea snail, a marine gastropod mollusk in the family Fissurellidae, the keyhole limpets.[1] Although similar in appearance to a common limpet, it has a hole near the apex of its shell, and is only distantly related. It often has a scaled polychaete worm Arctonoe vittata living inside its shell as a commensal. In the event that it is attacked by a starfish, it extends flaps of mantle to defend itself, and the worm also helps drive the predator away.
Diodora aspera has a cone-shaped shell growing to a length of about 7 cm (2.8 in). Near the apex is an aperture about one tenth of the length of the shell, which is used for respiration and the elimination of waste. There is a broad foot which exerts suction on the rock surface, and the mantle is large enough to cover the margin of the shell. The surface of the shell is sculptured with coarse ribs and is usually greyish-brown or grey, often with dark and pale radiating bands of colour.[2] The margin of the shell is crenulate and the interior is white.[3]
This species is native to the northeastern Pacific Ocean from Alaska to Mexico. It occurs in the lower part of the intertidal zone and the shallow sub-littoral, down to about 12 m (40 ft). It typically clings to the lower part and underside of rocks, but is sometimes found on the holdfasts and stalks of kelp. When the tide is out and it is exposed, it tends to always attach itself to the same spot, where its shell neatly fits the contours of the rock.[4]
When the tide comes in, this keyhole limpet crawls around, scraping bryozoans and algae off the rock surface with its radula. Certain species of sponges are also consumed. The sexes are separate and individuals with ripe gonads occur throughout the year. The eggs and sperm are shed into the sea where fertilisation takes place, and the larvae settle on the sea bed.[3]
This keyhole limpet is host to the ectoparasitic copepod Anthessius nortoni.[1] The scaled polychaete worm Arctonoe vittata acts as a commensal to D. aspera, living between the foot and the shell. This worm is relatively large, growing to a length of up to 10 cm (4 in), and may need to bend in order to fit. The worm is a predator, but does not attack its host, instead searching for prey to target as the limpet moves around. It is however willing to defend its host if a predacious starfish approaches, by biting at its tube feet.[5]
The keyhole limpet is also able to defend itself against attacks by starfish. On the approach of certain species of starfish, it swiftly extends and folds its mantle upwards to cover the shell, while another flap of mantle descends to cover the foot. At the same time, the inhalent syphon is extended through the aperture and covers the apex of the shell. As a result of these defensive actions, the starfish is unable to get a grip on the limpet shell with its tube feet; it is also possible that there is some chemical deterrent present in the mantle. At any rate, the starfish desists, and the limpet lowers its mantle after about twenty minutes. Not all starfish elicit this response, which is likely to be mediated by some chemical cue.[6]
Diodora aspera, also known as the rough keyhole limpet, is a species of sea snail, a marine gastropod mollusk in the family Fissurellidae, the keyhole limpets. Although similar in appearance to a common limpet, it has a hole near the apex of its shell, and is only distantly related. It often has a scaled polychaete worm Arctonoe vittata living inside its shell as a commensal. In the event that it is attacked by a starfish, it extends flaps of mantle to defend itself, and the worm also helps drive the predator away.
