| Dog whelk | |
|---|---|
 | |
| A group of liveNucella lapillus on thebarnacles which they eat. | |
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| Nucella lapillus shells | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Subclass: | Caenogastropoda |
| Order: | Neogastropoda |
| Family: | Muricidae |
| Genus: | Nucella |
| Species: | N. lapillus |
| Binomial name | |
| Nucella lapillus | |
| Synonyms[1] | |
Buccinum filosaGmelin, 1791 | |
Thedog whelk,dogwhelk, orAtlantic dogwinkle (Nucella lapillus) is aspecies ofpredatorysea snail, acarnivorous marinegastropod in the familyMuricidae, the rock snails.
Nucella lapillus was originally described byCarl Linnaeus in his landmark 175810th edition ofSystema Naturae asBuccinum lapillus (thebasionym).
This species is found around the coasts of Europe and in the northern westAtlantic coast of North America. It also can be found inestuarine waters along theAtlantic coasts. This species prefers rocky shores, where it eatsmussels andacorn barnacles.[2]
The dog whelk shell is small and rounded with a pointedspire and a short, straightsiphonal canal (a groove on the underside of the shell) and a deep anal canal. The overall shell shape varies quite widely according to the degree of exposure towave action of the shore on which a particular population lives but thebody whorl (the largest section of the shell where the majority of thevisceral mass is located) is usually around 3/4 of the total length of the shell.[3] Theaperture is usually crenulated in mature dog whelks, less often in juveniles.[4]
The shell surface can be fairly smooth interrupted only with growth lines, or when the snail is living in more sheltered areas the shell surface can be somewhat rough and lamellose. The surface is spirally corded. The outer lip is dentate and ridged within. Thecolumella is smooth.
The external shell colour is usually a whitish grey, but can be a wide variety of orange, yellow, brown, black, or banded with any combination of these colours. They can even, occasionally, be green, blue, or pink.
The dog whelk lives on rocky shores, and in estuarine conditions. Climatically it lives between the 0 °C and 20 °Cisotherms.[citation needed]
Wave action tends to confine the dog whelk to more sheltered shores, however, this can be counteracted, both byadaptations to tolerate it such as the shell and muscular foot, and by the avoidance of direct exposure to wave action afforded by making use of shelteredmicrohabitats in rocky crevices.[citation needed] The preferredsubstrate material of the dog whelk is solidrock and notsand, which adds to its problems at lower levels on the shore whereweathering is likely to have reduced the stability of theseabed.[citation needed]Water loss byevaporation has to be tolerated (by means of theoperculum which holds water in and prevents its escape asvapour), or avoided (by moving into water or a shaded area).[citation needed]
The peak in dog whelkpopulation density is approximately coincidental with the mid-tidal zone. It lives in the middle shore. In general it can be said that at high vertical heights on the shoreline the dog whelk is most threatened bybiotic factors such as predation from birds andinterspecific competition for food, butabiotic factors are the primary concern, creating a harsh environment in which it is difficult to survive.[citation needed] At low vertical heights it is biotic factors, such as predation from crabs andintraspecific competition, which cause problems. The upper limit of the range in which the dog whelk is generally found is approximately coincidental with the mean high waterneap tide line, and the lower limit of the range is approximately coincidental with the mean low waterneap tide line, so that the vast majority of dog whelks are found on the mid-tidal zone.[citation needed]
Tidal pools and comparable microhabitats extend the vertical range oforganisms such as the dog whelk as they provide a more constant environment, but they are prone to increasedsalinity because evaporation concentrates dissolved substances. This can createtoxic conditions for many species.[citation needed]
The dog whelk can only survive out of water for a limited period, as it will gradually becomedesiccated and die.Metabolic processes within cells take place in solution, and a decrease in water content makes it impossible for the organism to function properly. In experiments it has been shown that 50% of dog whelks die at 40 °C. The dog whelk has toexcrete ammonia directly into water, as it does not have the adaptation possessed by many upper shore species which would allow it to produceuric acid for excretion without loss of water. When kept emersed for seven days at a temperature of 18 °C, 100% of dog whelks die, in contrast to manyperiwinkle species which can lose even more water than the dog whelk (i.e. more than 37% of their total body mass) but survive as a result of their ability to excrete toxic waste products more efficiently.[citation needed]
Itsadaptations include a modifiedradula (a toothedchitinous structure) to bore holes in theshells ofprey, complemented by anorgan on the foot which secretes a shell-softening chemical. When a hole has been formedparalysing chemicals anddigestive enzymes are secreted inside the shell to break the soft body down into a 'soup' which can be sucked out with theproboscis. The plates of barnacles can be pushed apart with the proboscis, and the entire individual is eaten in about a day, although larger animals such as mussels may take up to a week todigest.
Feeding only occurs when conditions are conducive to such an activity, and during these times the dog whelk consumes large quantities of food so that thegut is always kept as full as possible. This allows shelter until more food is required, whenforaging resumes. Ifwaves are large or there is an excessive risk of water loss the dog whelk will remain inactive in sheltered locations for long periods.[citation needed]
Mussels have developed a defensive strategy of tethering and immobilising with byssus threads any dog whelks invading their beds, leading to the whelks' starvation.[5]
Nucella lapillus's feeding activity is suppressed on brighter moonlight nights, in order to minimize predation risks. High-intensity ALAN levels reversed the pattern. In fact,N. lapillus would more likely forage when Artificial Light At Night (ALAN) intensities range from 10 to 50 lx, which are way higher than lunar brightness. This allows dog whelks to easily exclude predation risk.[6]
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Predators of the dog whelk include various species ofcrabs andbirds. Protection againstpredation from crabs which attempt to pull the soft body out through the shellaperture can be afforded by growingteeth around the edge of the aperture.[citation needed] Many predators cannot smash the strong shell of an adult dog whelk, butjuveniles are vulnerable to attack from many predatory species.[citation needed]Eider ducks and various other birds simply swallow the entire body with its shell, whileoystercatchers and variouscrustaceans are often capable of crushing or breaking the shells.[citation needed] In the winter they endure more predation frompurple sandpipers and similarwading birds, but in the summer crabs represent a greater threat. In general, the dog whelk can be thought of as being vulnerable to birds when emersed, and to crabs when immersed.[citation needed]
The dog-whelk can be used to produce red-purple and violet dyes,[7] like its Mediterranean relations the spiny dye-murexBolinus brandaris, the banded dye-murexHexaplex trunculus and the rock-shellStramonita haemastoma which provided thered-purple and violet colours that the Ancient World valued so highly.[8]Bede mentions that in Britain "whelks are abundant, and a beautiful scarlet dye is extracted from them which remains unfaded by sunshine or rain; indeed, the older the cloth, the more beautiful its colour."[9]
In Ireland, on the island ofInishkea North, Co. Mayo, archaeologists found a whelk-dyeing workshop, dated to the 7th century AD, complete with a small, presumed vat, and a pile of broken-open dog-whelk shells.[10] Unfortunately, no such workshop is known from Britain for the early medieval period. However, a double-checked trace of bromine, indicating the presence of whelk-dye, has been found on one page of an Anglo-Saxon book known as theBarberini Gospels. This manuscript dates to the late 8th or early 9th century AD, and the whelk dye occurs as a background panel to white lettering at the beginning of St John's gospel. Efforts have also been made to find whelk dye on surviving fragments of Anglo-Saxon textiles, but the chemical analyses so far carried out have proved negative for bromine.[11]
AnAnglo-Saxon account of the accession ceremony ofAldfrith of Northumbria involved whelk-dyed cloth, although this may simply be a poetic echo of Roman ceremonies. Another example involves an account of valuable textiles brought to England byWilfrid of Ripon.[12]
