Just a Common Whelk Shell (4)

Posted on August 19, 2014 by winderjssc

Empty Common Whelk shell with calcareous tubes attached

This empty Common Whelk shell, picked up on the beach, is mostly covered with the calcareous tubes of a marine polychaete worm called Pomatoceros triqueter, also known as “German writing”. The tubes are a frequent sight on rocks at the beach and also on objects such as pebbles and driftwood. The tubes attached to the outer surface of the shell may have been made while the whelk was still alive and moving about. Those within the mouth of the empty shell were definitely attached after the gastropod mollusc had died and its flesh had been removed from the shell.

Organisms that live on the outside of other creatures in this way are known as epibionts. Usually epibionts are neither parasites that occupy a rather one-sided relationship with the host where they rely on it for nutrients and frequently damage it; nor symbionts where both organisms depend on each other in a mutually beneficial relationship; but maybe they could be called commensals in that the host is not damaged by the attached organism but merely provides a surface of attachment, and both organisms share the same environment.

The images below show the distinct patterns where calcareous tubes of Pomatoceros triqueter have been attached (but now removed) on a pebble at Chesil Cove in Dorset; also some in situ shots of Pomatoceros tubes attached to low shore rocks, along with the sand-grain tubes of the Honeycomb Worm (Sabellaria alveolata), at Mewslade Bay in Gower.

Calcareous and sandgrain tubes of marine worms on rocks at low tide

Pattern of marks where the calcareous tubes of Pomatoceros were once attached to a pebble

Just a Common Whelk Shell (3)

Posted on July 12, 2014 by winderjssc

Whelk shell with an encrustation of mostly acorn barnacles – some complete with all plates and in other areas only the basal plate remains

Acorn Barnacles (Cirripedia) settle on almost anything in the sea or on the seashore. These images show the empty shell of a Common Whelk (Buccinum undatum) that I picked up on the beach at Rhossili on the Gower Peninsula in South Wales – it has proved to be an ideal substrate for them.

The outer surface of the shell is almost entirely covered with barnacles. The majority are intact with the lateral and also the terminal plates. Many specimens are mature but there are juveniles too. In one area, the barnacles have been knocked off but you can still see the basal plates by which they were attached. Some barnacles may have been living on this common British seashell while it was still alive. However, it is equally possible that the shell became colonised by barnacles once it was empty. The few calcareous tubes of marine worms which are stuck on the inner surface of the aperture or mouth of the shell would have settled there once the whelk flesh had disappeared.

The close-up shots reveal the details of the structure of the barnacles, made up generally from six fixed lateral plates overlapping each other to form the shell for the animal, with four articulating terminal plates forming the lid to the chamber. The whole barnacle shell is in this instance securely attached to the whelk shell by a basal plate that often remains in place even when the barnacle becomes detached. Not all species of barnacle have a basal plate.

The macro-photographs also show the intricate pattern and texture of the whelk shell surface with a regular criss-crossing of ridges. This gives an almost lattice-like effect where the growth lines intersect with the natural ornamentation or sculpturing of the shell. In close-up, it is also possible to see small areas of the colonial microscopic animals called Bryozoa or Sea Mats (resembling fragments of lace) which are clinging to the bases of some of the barnacle shells.

Macro-photograph of growth lines and natural sculpturing on a whelk shell

Close-up image of pattern and texture in a barnacle-encrusted whelk shell

Whelk shell with mature and juvenile barnacles attached

Close-up image of growth lines and natural sculpturing in a barnacle-encrusted whelk shell

Apertural view of epibiont encrustation hard parts on a Common Whelk shell

Whelk shell with barnacles attached to the outside and calcareous tubes inside

Just a Common Whelk Shell (2)

Posted on July 2, 2014 by winderjssc

Close-up, even the most common seashell picked up on the beach has a wealth of detail in its colour, pattern, and texture that tell the story of what it is and the life it has led, stage by stage: the shape and form, the size, the inherent sculpturing, the fine growth lines, breaks, scarring, and staining. Unusually, this Common Whelk shell (Buccinum undatum) has no attached epibiont organisms like barnacles or sea mats, or evidence of boring organisms like marine worms and sponges. Its black and orange staining show that it has spent some time buried in the sand near the top of the boundary from 5 – 15 cm deep that is a gradation between the anoxic black sediment where mostly only anaerobic bacteria thrive – and the yellow sand above which has enough free oxygen to support the life of immense populations of micro-organisms and to decompose their waste products.

A Hermit Crab from Rhossili

Posted on November 24, 2011 by winderjssc

This sea shell has a secret. It is the new home of a Hermit Crab, Pagurus bernhardus (Linnaeus). He is very shy. I had to wait very patiently for him to come out of his shell – and then he nearly ran into the lens of the camera!

Revision of a post first published 13 September 2009

COPYRIGHT JESSICA WINDER 2011

Funny flotsam fish

Posted on August 30, 2011 by winderjssc

This funny, flippy-floppy silicone rubber fishing lure was found on the strandline at Whiteford Sands. It’s very realistic. It has great googly eyes and even the scales are painted on the body. It feels wet and sticky and wobbles when you pick it up. Originally it was lying amongst empty dark blue mussel shells on the wet sand. I couldn’t resist picking it up and taking it home. Now it resides in the bright blue bowl of beach-combed shells on my window sill.

Revision of a post first published 10 January 2010

COPYRIGHT JESSICA WINDER 2011

Growth line patterns in whelk shells

Posted on May 15, 2011 by winderjssc

Yesterday I talked about the basic structure of a whelk shell and described a few of its characteristic parts. Today, the photographs illustrate those points in a number of different whelk shells.

The textures and patterns of gastropod mollusc shells, like those belonging to the Common Whelk (Buccinum undatum L.), are very different from those found in bivalved shells described in earlier posts. The pictures in this post show the variations and intricate details of the ridges, furrows, and grooves of the striations – crossed by diagonal broad ribs and fine growth lines in whelk shells – resulting in a slightly chequered or reticulated pattern on the smaller scale as well as the more obvious one typified by parallel ridges. There is evidence for breakages and repair in some specimens. Older, larger shells have seemingly experienced minor damage to the outer lip and mantle edge that has contributed to thick ridges parallel to the aperture.

You can also see the remains of a selection of the marine organisms that commonly attach themselves to the outer surface of the shells. The encrustations include the sinuous calcareous tubes of marine polychaete worms such as Pomatoceros triqueter; lace-like layers of seamat or Bryozoa; and empty acorn barnacle shells. The brown, hairy, paper-like coating on some specimens is the outermost layer of the shell – the periostracum. This is present on younger, smaller shells but soon wears away when the mollusc reaches maturity.

The most distinct sculpturing or ornamentation on the shells is seen in the young specimens, especially where the protective periostracum has just peeled away. Older, more worn shells, tend to lose the crisp, glossy outer surface and look slightly furry in close up – due no doubt to the disintegration of the shell crystal structure.

Revision of a post first published 7 April 2010

COPYRIGHT JESSICA WINDER 2011

Parts of the shell – Common Whelk

Posted on May 14, 2011 by winderjssc

It is useful to know a few simple terms that describe the different parts of seashells. This special terminology defines the particular features of a shell that distinguish one species from another. It also helps to know these words in order to understand accounts of the development of the creatures, their biology and life history.

I am starting with a few names of basic parts in a gastropod mollusc shell. The example illustrated is the Common Whelk – Buccinum undatum Linnaeus. A gastropod shell is like a long, tapering tube or cone that has been coiled up. The top of the coiled shell, where the diameter of the tube is at its smallest, is called the apex of the shell.

Each complete turn of the shell tube, each coil, is known as a whorl. The areas where the whorls touch and join each other are called sutures. As the living animal grows, the diameter of its shell increases. Most of the body of the animal is housed in the last large whorl, the body whorl, leading to the mouth or aperture of the shell. Typically the snail can protrude from the aperture or withdraw into it. The whorls above the body whorl are termed the spire. The spire can be short and squat (like in a Necklace Shell) or drawn out to form a point (as in the Common Whelk).

The flesh of the animal is covered by a layer of tissue called the mantle. The mantle makes the shell. The shell is made up of three layers. The inner and middle layers of shell are composed of calcium carbonate crystals arranged on a framework of an organic, protein-like material called conchyolin.

The smooth inner or nacreous layer of the shell is continually secreted by the overall surface of the mantle with which it is in continuous contact. In some species of mollusc this is a layer of iridescent ‘mother of pearl’. The thin sheets of crystalline calcite that make up this inner layer lie more or less parallel to the surface. The inner layer grows in thickness throughout the life of the animal.

Around the aperture, the edges of the mantle produce the middle layer of the shell which comprises crystals of aragonite lying at right angles to the surface. This layer stops getting bigger when the mollusc becomes adult.

The outermost layer of the shell is the periostracum. This is also formed by the edge of the mantle and stops growing on sexual maturity. It has no calcium carbonate crystals and is entirely made of conchyolin. It is thin and easily worn away and rarely seen in mature gastropods.

The outer calcareous layer of the shell has patterns and textures that are typical of the species. Spiralling around the shell of the whelk, along the length of the ‘tube’ as it coils, is a series of narrow ridges and grooves called striations. Running diagonally across the striations, and curving right over each whorl, are thick ribs. On a much finer level, very fine growth lines loop the circumferance of the ‘ tube’ of the shell, and intersect the striations.

The next posting on Jessica’s Nature Blog will show photographs and detailed close-ups of the patterns and textures made by growth lines and sculpturings on the outer surfaces of Common Whelk shells. It will also further illustrate some of the features mentioned here.

Revision of a post first published 6 April 2010

The Common Whelk (1)

Posted on May 13, 2011 by winderjssc

A pink-shelled living specimen of Common Whelk, Buccinum undatum Linnaeus, washed onto the rocks of Burry Holms on Rhossili Bay, Gower, after stormy winter weather.

Until a couple of years ago, the only place where I had seen the meaty part of a Common Whelk was at the fishmongers. I had no idea that the living animal could be such a lovely creature. The specimen at the top of this post unexpectedly had a beautiful pink shell. Its living flesh was white with black irregular speckles – particularly concentrated at the head end. You can see the two horns or cephalic tentacles sticking out on each side of the head.

On the back of the large muscular white foot is the brown horny operculum which is the lid with which it seals itself inside the shell when it retreats. Protruding from the front end of the shell, just over the head, is the tubular siphon through which is takes in water.

Mostly, in the past, I have just found the empty shells on the beach. The colour can be quite variable. The close-up photograph above shows a fairly typical brown and cream coloured shell and it is possible to see some details of the shape and sculpturing of the shell. At a later date I will provide some specific details of how to accurately identify the shell. I will also talk a bit about the life history of the Common Whelk.

The picture below shows a group of empty shells in various colours from cream and white, to orange and a dark blue/black. These were found on Whiteford Sands in Gower.

Revision of a post first published 7 July 2009

Common Whelk shells with barnacles attached

Posted on January 31, 2010 by winderjssc

The shells of the Common Whelk, Buccinum undatum Linnaeus, are shown here with an encrustation of acorn barnacle shells. I often display the shells and other beachcombings I bring home from the seashore in bowls and baskets on my window sill; and these make suitable containers in which to photograph objects for the Jessica’s Nature Blog.

I particularly like dishes with glazes that remind me of the seashore; so I was delighted when I discovered the beautiful blue/green glazed terracotta platter that I have used for today’s photograph. It is made by a studio potter called Rosemarie James who uses layers of rich-coloured glazes to create a depth, richness and movement that is reminiscent of the sea, the sky, and natural forms along the Dorset coast. A perfect complement and frame to the natural shell forms.

Common Whelk shells from Swansea Bay

Posted on January 29, 2010 by winderjssc

The thousands of Common Whelk shells that I discovered on the sandy beach of Swansea Bay in the New Year were remarkably different from the ones I have previously picked up at Rhossili Bay and Whiteford Sands. The whelk shells were smaller here, about half the size of the Gower specimens. The shells were also thinner with many of them sporting broad brown spiral bands – as you can see from the photograph above. I think the Swansea shells were from younger animals. A few had been stained orange by burial in the sand and others had barnacles and calcareous worm tubes attached.

The whelk shells were found together with slipper limpet shells, mussels, cockles, necklace shells and razor clams. There were also many small delicately tinted pink and yellow bivalves such as tellins. Seashells were liberally scattered on the wet sand as well as occurring in thick accumulations on an almost continuous strandline high up the shore. This strandline was unusual in containing many twigs and leaves from the trees that border the bay – reflecting the residential and cultivated backdrop to the shore. While the influence of the port and heavy industries not too far away was shown by the large amount of water worn coal in the strandline. The dark oak leaves, black ‘pebbles’ of coal, and the multitudes of blue-black mussel shells gave the strandline its characteristic dark colour – against which the other bivalves and gastropods gleamed luminously in the bright, slanting winter sunshine.

Click here for more information about the Common Whelk (Buccinum undatum L.) in earlier postings in Jessica’s Nature Blog.

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Tag Archives: Common Whelk

Just a Common Whelk Shell (4)

Just a Common Whelk Shell (3)

Just a Common Whelk Shell (2)

A Hermit Crab from Rhossili

Funny flotsam fish

Growth line patterns in whelk shells

Parts of the shell – Common Whelk

The Common Whelk (1)

Common Whelk shells with barnacles attached

Common Whelk shells from Swansea Bay