Just a Common Whelk Shell (4)

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.

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Just a Common Whelk Shell (3)

Lots of barnacles on a whelk shell

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

Barnacle encrustation on a whelk shell

Whelk shell with mature and juvenile barnacles attached

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

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

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Just a Common Whelk Shell (2)

Study of a Common Whelk shell

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.

Detail of growth lines and pattern in a Common Whelk shell

Study of a Common Whelk shell

Close-up image of seashell texture

Study of a Common Whelk shell

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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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