''Diodora aspera'', also known as the rough keyhole limpet, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a marine

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Fissurellidae, the keyhole limpets. Although similar in appearance to a

common limpet ''Patella vulgata'', common name the common limpet or common European limpet is a species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often ...

, it has a hole near the apex of its shell, and is only distantly related. It often has a scaled polychaete worm ''

Arctonoe vittata ''Arctonoe vittata'' is a species of scaled polychaete worms commonly known as a "scale worm". This species often lives as a commensal of another marine animal. Description At least thirty pairs of elytra, scale-like modifications to the dorsal ...

'' living inside its shell as a commensal. In the event that it is attacked by a

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

, it extends flaps of

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

to defend itself, and the worm also helps drive the

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

away.

Description

''Diodora aspera'' has a cone-shaped shell growing to a length of about . 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. The margin of the shell is crenulate and the interior is white.

Distribution

This species is native to the northeastern Pacific Ocean from

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

. It occurs in the lower part of the intertidal zone and the shallow sub-littoral, down to about . 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.

Ecology

When the tide comes in, this keyhole limpet crawls around, scraping

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

ns and

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

off the rock surface with its

radula The radula (, ; plural radulae or radulas) is an anatomical structure used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food ...

. 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. This keyhole limpet is host to the ectoparasitic

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

'' Anthessius nortoni''. The scaled polychaete worm ''

'' 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 , 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

approaches, by biting at its

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on britt ...

. 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.

References

* Turgeon, D., Quinn, J. F., Bogan, A. E., Coan, E. V., Hochberg, F. G., Lyons, W. G., Mikkelsen, P. M., Neves, R. J., Roper, C. F. E., Rosenberg, G., Roth, B., Scheltema, A., Thompson, F. G., Vecchione, M., Williams, J. D. (1998). Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks. 2nd ed. American Fisheries Society Special Publication, 26. American Fisheries Society: Bethesda, MD (USA). ISBN 1-888569-01-8. IX, 526 + cd-rom pp.

External links

*
Gould A.A. (1846). Descriptions of new shells, collected by the United States Exploring Expedition. Proceedings of the Boston Society of Natural History. 2:
{{Taxonbar, from=Q3168571 Fissurellidae Molluscs of the Pacific Ocean Taxa named by Martin Rathke Gastropods described in 1833