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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Miscellaneous Seashells

Black-lined Periwinkle Seashells

Black-lined Periwinkle seashells (Littorina nigrolineata)

Banded Wedge seashells

Banded Wedge seashells (Donax vittatus)

Turban Top seashells

Top Shells (Gibbula spp.)

Variegated Scallop seashells

Small Scallop  seashells (Chlamys sp.)

Dog Whelk Seashells

Dog Whelk seashells (Nucella lapillus)

Common Cockle seashells

Common Cockle seashells (Cerastoderma edule)

Netted Dog Whelk seashells

Netted Dog Whelk seashells (Hinia reticulata)

Small Scallop seashells and Manila Clam

Small Scallop seashells (Chlamys sp) and Manila Clam

Common Whelk seashells

Common Whelk seashells (Buccinum undatum)


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Common Winkle


Seashore Creatures: Molluscs: Gastropods: 

Common Winkle Littorina littorea (Linnaeus)

  • This has a small, squat and robust spired shell upto 30mm high.
  • The rounded shape and the thick shell protect the animal from damage caused by the force of the waves and rolling around when they are dislodged from rocks.
  • The animal can withdraw into the shell and shut itself inside with a horny lid or operculum to stop it being dried out when it is exposed to the air at low tide. 
  • Seems to have a smooth surface but actually has numerous fine spiral ridges around the whorls which are more obvious in younger shells.
  • The final identifying characteristic for the species is the way the outer lip of the aperture joins the last body whorl at a tangent.
  • The shell is usually a dark grey-brown colour but it can be paler at the pointed spire end and the colour gets paler as the winkle grows older (as you can see in the photograph at the top of this page).
  • In the shells of younger winkles there may be red, orange or white colour in the grooves between the fine ridges (this can be seen in the photograph at the top of the Post for 11th February 2009).
  • The head tentacles have many cross-wise black stripes.
  • Winkles live on the upper (intertidal) shore down to the shallow sublittoral (underwater) zone.
  • They are herbivores that love weedy shores and are found in greater numbers on more sheltered beaches.

For more information about the common winkle see the Marine Life Information Network:

Book references to common winkle include:

  • Barrett, J. and Yonge C. M. (1958 but reprinted many times) Collins Pocket Guide to the Seas Shore, Collins, ISBN 0 0 219321 3, page 135.
  • Gibson, C. (2008) Pocket Nature Seashore, Dorling Kindersley, ISBN 978 1 4053 2862 3, page 116.
  • Graham, A. (1971) British Prosobranch and Other Operculate Gastropod Molluscs, Keys and notes for the identification of the species, Synopses of the British Fauna No. 2, The Linnaean Society of London, Academic Press, ISBN 0-12-294850-5, page 53 & 58.
  • Hayward, P. J.  and Ryland J. S. (1995) Handbook of the Marine Fauna of North-West Europe, , Oxford University Press, ISBN 0 19 854055 8 (Pbk), page 512.
  • Hayward, P., Nelson-Smith, A. and Shields, C. (1996) Sea shore of Britain and Europe, Collins Pocket Guide, , ISBN 0 00 21995, page 188.  



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Strandline Seashells in situ

Common British seashells on the strandline

These pictures show natural accumulations of common British seashells on the strandline at Rhossili, Gower, South Wales. They are photographed as found – in situ. The images have a usefulness and significance despite the fact that that they are neither technically brilliant photographs nor what you might call picture postcard shots. They probably wouldn’t win any prizes for beauty or be worthy of framing on the wall.

The pictures show nature as it really is – without re-arrangement, clever angles, or just the right lighting. Their function is to inform rather than visually please. They are a way of recording something both situational and ephemeral, something that may only last a few hours until the next tide, something that may not occur in the same way again for months, if ever. From these jumbled up assortments of shells it is possible, for example, to compile a species list of marine molluscs that until recently lived in the area, not just the shore on which they were deposited, but including a geographically wider variety of habitat substrates, water depths, and degrees of exposure, that have been scoured by the waves, currents and tides.

In the instance of the pictures posted here, the random selections of shells do not represent death assemblages (mass mortalities) which often occur on this and other beaches. Actually, many of the shells, particularly the more robust ones like oysters and limpets, may be decades or even centuries old; the more fragile shells (like those of Banded Wedge Shells) readily break up in a very short time. Thicker, older shells have become incorporated with more delicate shells, from recently dead organisms, all the shells undergoing a cycle of burial and release from the sediments, a process which over time leads to more and more breakages, infestation damage, and burial staining, and general abrasion that leads to the eventual destruction of the shells and incorporation into the finer beach sediments.

This kind of temporary strandline deposit of shells and shell fragments could provide insights into the origins and processes involved in the formation of fossil shell assemblages. It could potentially provide clues to past and changing environments. It might allow understanding and interpretation of archaeological deposits of shells. It is not possible to know every way in which the information might turn out to be useful. So I have recorded it for posterity and future science investigations – just in case.


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Just a Common Whelk Shell

Common Whelk Shell (1) - Empty shell of the common British marine gastropod mollusc - Buccinum undatum (Linnaeus).

Many seashells, like that of the Common Whelk Buccinum undatum (Linnaeus), show a lot of individual variation in size, shape, growth line patterns, colour, encrustation, and general wear and tear.  That’s what makes the shells so interesting and attractive to look at – even if they do not feature bright colours and exotic designs.

So this marks the first in an occasional series of postings – each showing an individual shell from various different view points to demonstrate macroscopic variability in appearance within different species of common British seashells.

Clicking on a photograph will enlarge the image so you can see the details.

Click here for more information and illustrations on whelks and whelk shells in Jessica’s Nature Blog.


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Arrangements of Seashells

Arrangement of Seashells 1 - Mostly small variegated scallop shells with a Manila Clam, top shells, and sea glass, in a bowl of water - common British seashells.

I really like to look at shells and have them around me. I often discover the odd shell in my pocket as a souvenir of a trip to the beach. Sometimes I will collect empty shells in larger numbers where this is permitted. The pictures in this post show different assortments and arrangements of common British seashells that have decorated my home from time to time over the last couple of years.

There are many posts on Jessica’s Nature Blog about seashells – sometimes just showing pretty pictures (like here) but often also describing their identifying features and other information. Click here if you would like to browse through more than 60 SEASHELL POSTS.


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Parts of the shell – Common Cockle

Blue bowl of cockle shells on my sunny window sill

This is a bowl of different kinds of cockle shells on my window sill. Seashells seem to have a universal appeal. Like me, many people cannot resist picking up empty shells from the seashore and taking them home as a seaside souvenir. Shells come in all sorts of shapes and sizes. It is the details of the structure that provide the clues to the identity of the shell – that tell you not only what type of creature it is, and its life habits, but also give it its scientific name – one that is unique to that particular species.

Size, shape, colour, and texture all contribute to species identification in marine molluscs. Each part of the seashell has a particular name. Differences in the characteristics of the different parts can be used to distinguish between one species and another.

 In this post, I am describing the some of the features of a common British bivalved shell, using as an example the basic outer parts of the Common Cockle shell – Cerastoderma edule (Linnaeus) – which are labelled in the photographs shown below. [In later posts I will explain more details about the exterior of cockle shells and then the inside of them].

Cockles are one of the best known members of the group of molluscs known as Bivalvia, also called Lamellibranchia and Pelecypoda. The soft body of the animal is enclosed by two hard calcareous valves or shells. All bivalves are aquatic (marine, brackish, and freshwater), with a structure that is an adaptation to living in softer sediments like mud or sand, but also can be modified for boring into harder solid substrates like clay, wood and stone.

We are told in British Bivalve Seashells by Norman Tebble (published by The British Museum (Natural History) 1966, ISBN 0 11 491401 X) that the shell of the common edible cockle is solid and the two halves or valves of the shell are similar in shape and sculpture (equivalve). However, the shape of the valves themselves differs from the front end (anterior) to the back end (posterior) on either side of the beak and umbo (the oldest part of the shell found in a dorsal or top position near the hinge). The valve itself is therefore asymmetrical or inequilateral. The beaks are in front of the mid-line.

The outline of the shell is broadly oval, with a continuous curve around the anterior edge or margin at all stages of growth; while the posterior margin of the shell becomes less curved as the cockle ages. The shell is a naturally a dirty white, pale yellow or brown in colour and some staining can occur from the sediments in which it buries. Cockles are marketed at about 1 inch (2.5 cm) long but they can actually grow much larger – up to 2″ (5 cm).

The ligament is a band of fibres in the hinge between the two valves. In the cockle, the ligament is a prominent dark brown, arched band. It acts to pull apart the two valves. The animal inside the shell actively contracts its adductor muscles to keep the valves shut. If these adductor muscles relax, then the springy properties of the ligament automatically pull the shells apart and open the shell. Another name for the external ligament is tensilium.

The outer surface of each valve has 22 – 28 radiating ribs, each with numerous scale-like spines. There are numerous fine irregular concentric lines and more pronounced concentric rings which represent shell growth increments on shorter and longer time-scales respectively.

Click here for more photographs and information about cockles.

[In an earlier post I explained some of the parts of a typical gastropod shell using the Common Whelk – Buccinum undatum Linnaeus.]

Common Cockle - anterior view

Common Cockle - dorsal view

Common Cockle - posterior view


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