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The Common whelks appearance
The common whelk is one of the largest snails
in European waters, an adult snail can be up to 11cm long and 7cm wide.
The shell has a yellow-brown colour, while the body is grey-white with black
patches. The body consists mainly of an intestinal sack and a creeping
sole known as a foot. The anterior of the foot passes over into the
head with a pair of eye furnished tentacles.
The eyes are relatively primitive and can probably only discern between
varying light intensities. The anterior of the head extends into a siphon,
also known as the proboscis. At the end of the siphon the mouth is situated
and surrounded by muscles that control the jaws that hold the food and the
rasp tongue that dismember it. Because of the trunk like siphon, the whelk
is able to reach food that is protected by a shell. By pushing its siphon
between the two shell halves, the whelk can eat a mussels soft parts from
the inside.
In the foot and the head, the main parts of the nervous and
digestive system are found. On the posterior of the foot, the so-called
operculum is found, a hard plate
that functions as a lid to the shell which the snail pulls into place. The
intestinal sack, which is covered by the shell, contains the remainder of
the digestive system, ovary/testicles, heart and the kidney. Here, a so-called
mantle hole is situated and where the gills are found aswell as an opening
for the anus, kidney and reproductive organs.
The common whelk has only one sex, with either a testicle or
an ovary which takes up a large area of the intestinal sack. The calcareous
shell is secreted from glands on certain parts of the body. the calcareous
secretion is deposited partly to increase the thickness of the shell, and
partly to increase the shell size around the opening. The characteristic
whorl shape of the shell is a result of that the glands at the outer edge
secrete calcareous material quicker than the glands along the inner edge.
Shell growth varies during the year and gives rise to apparent areas of
growth.
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