A Hermit Crab from Rhossili

Seashell with a secret. Common Whelk shell (Buccinum undatum) in which a Hermit Crab (Pagurus bernhardus) is living on Burry Holms, Rhossili, Gower, South Wales (1)

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!

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales(2)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (3)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (4)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (5)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (6)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (7)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (8)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (9)

Hermit Crab (Pagurus bernhardus) emerging from a Common Whelk shell (Buccinum undatum) at Burry Holms, Rhossili, Gower, South Wales (10)

Revision of a post first published 13 September 2009

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Funny flotsam fish

Funny flotsam fishing lure in a bowl of whelk shells on my window sill (1) 

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.

The head of the fish-shaped fishing lure with a big googly eye - found on the strandline at Whiteford Sands, Gower, West Glamorgan (2)

The painted fish scales on the body of the fishing lure washed up at Whiteford Sands, Gower, West Glamorgan (3)

The wibbly-wobbly fish-shaped fishing lure where it was found among the mussel shells on the strandline at Whiteford Sands, Gower, West Glamorgan (4)  

Revision of a post first published 10 January 2010

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Growth line patterns in whelk shells

 Growth lines in the Common Whelk shell: Common Whelk shell, Buccinum undatum Linnaeus, showing growth lines and attached calcareous worm tubes - Lateral view (1)

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.

Gastropod shell growth lines: Shell of the Common Whelk (Buccinum undatum Linnaeus) showing growth lines - End-on view (2)

Whelk shell detail: Close-up detail of the pattern on a Common Whelk shell (Buccinum undatum Linnaeus) showing the striations intersected at right angles by the growth lines (3)

Regrowth in a damaged whelk shell: Shell of a Common Whelk (Buccinum undatum Linnaeus) showing growth lines and healing after damage to the shell aperture margin (4)

Colour banding and growth lines in common whelk shell: Shell of a Common Whelk (Buccinum undatum Linnaeus) showing growth lines, striations, ribs, and natural colour banding (5)

Growth and healing marks in a whelk shell: Close-up detail of the pattern on the body whorl of a Common Whelk shell (Buccinum undatum Linnaeus) showing regular growth lines and 'scarring' episodes crossing the even ridges and grooves known as striations (6)

Common Whelk shell: The shell of a Common Whelk shell (Buccinum undatum Linnaeus) showing the apex, spire, and body whorl with natural ornamentation of ribs, striations, and growth lines (7)

Close-up image of the spire texture in a young common whelk shell: The spire of a Common Whelk shell (Buccinum undatum Linnaeus) showing the coarse thick ribs, fine ridges and grooves, and growth lines freshly revealed from beneath the brown papery periostracum layer (8)

Macro photograph of shell pattern and texture in a Common Whelk: Detail of the pattern made by growth lines, striations, and colour bands on the body whorl of a Common Whelk shell (Buccinum undatum Linnaeus) (9)

Gastropod periostracum remants on young whelk shell: Growth line patterns on a Common Whelk shell (Buccinum undatum Linnaeus) still partially covered with the thin brown horny periostracum (10)

Empty Common Whelk shell (Buccinum undatum Linnaeus) showing growth lines, ornamentation, and natural brown colouring (11)

Macro photograph texture of worn whelk shell: Detail of the pattern and texture on a worn Common Whelk shell (Buccinum undatum L.) (12)

Revision of a post first published 7 April 2010

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Parts of the shell – Common Whelk

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

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The Common Whelk (1)

Common Whelk: Pink shelled living specimen of Common Whelk, Buccinum undatum Linnaeus, on rocks at Burry Holms, Rhossili, Gower, South Wales, U.K. (1)

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.

Whelk shell with pattern of growth lines: Brown and cream coloured empty Common Whelk shell, Buccinum undatum L., showing the pattern of growth lines, from Rhossili Bay, Gower, South Wales, U.K. (2)

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.

Different coloured Whelk shells on a sandy beach: A group of white, orange and dark blue empty Common Whelk shells, Buccinum undatum L., on Whiteford Sands, Gower, South Wales, U.K. (3)

Revision of a post first published 7 July 2009

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Common Whelk shells with barnacles attached

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. 

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Common Whelk shells from Swansea Bay

 

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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Starfish riding a Common Whelk

On New Year’s Eve a couple of years ago, winter storms had stirred up the seabed offshore, dredging up all the marine invertebrates like Razor Shells, Common Starfish, Brittle Stars, Spiny Cockles, Common Whelks, and much more. These were lifted up by the waves and tossed high on the shore with a lot of debris and empty shells in abundance. Some of the animals struggled to survive and others profited from the feeding opportunity provided by the mass stranding. All were mixed up together – the dead and the quick. Maybe the starfish were just searching for firm substrates but a lot seemed to home-in on the roaming and predatory whelks – attaching themselves firmly to the shells and seeming to hitch a ride on the large gastropods.

 

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Black Whelk shells from Whiteford

These empty shells of the Common Whelk, Buccinum undatum L., were originally lying randomly on the sandy strandline at Whiteford in Gower. I photographed this arrangement on a layer of fine beach gravel because I liked the complementary colours and contrasting textures. The natural sculpturing of growth lines, ridges, and grooves on the whorls of this gastropod mollusc shell are emphasised by the dark hues. In natural sunlight the black staining looked almost navy blue. The dark colour has been acquired by a period of burial deep in the beach sediments.

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