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

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Mother of Pearl 2

Mother of pearl decorative inlay on a 16th century Japanese coffer

Mother of Pearl from tropical seashells decorates this fabulous Kyoto Japanese coffer made for the European market around the end of the 16th century and beginning of the 17th century. The pieces of rainbow-hued iridescent shell are held in place by gilded copper rivets on a black and gold lacquered wood base (On display in the Victoria and Albert Museum, London; FE.33-1983).

Mother of pearl decorative inlay on a 16th century Japanese coffer

Mother of pearl decorative inlay on a 16th century Japanese coffer

Mother of pearl decorative inlay on a 16th century Japanese coffer

Mother of pearl decorative inlay on a 16th century Japanese coffer

Mother of pearl decorative inlay on a 16th century Japanese coffer

Mother of pearl decorative inlay on a 16th century Japanese coffer

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Mother of Pearl 1

Ornamental iridescent veneer of mother-of pearl on an 18th century  bureau-bookcase

Mother of pearl is a wonderful iridescent material that is frequently used for artistic purposes. It comes from the inner surface of certain shells, sometimes gastropods like the Button Top Shell, and other times from bivalves such as the Freshwater Pearl Mussel. The inner or nacreous layer of certain shells is composed of crystals which are arranged in layers that reflect light in an attractive way. The colours reflected, and the intensity of the sheen, depend on the type of shell from which it has been obtained and also on the quality of light to which it is exposed. The same piece of mother of pearl can look different in different lights.

The photographs here show the details of the decorative veneer on a bureau-bookcase probably made in Mexico between 1780 and 1820. This is one of many fine items of antique furniture displayed in the Victoria and Albert Museum in London. The veneer is composed of about 7,000 individual pieces of shell, each piece from a separate individual shell (most likely freshwater mussel), and each one having taken about 40 minutes to prepare and shape. The shape of every shimmering piece is highlighted to great effect by a very narrow border of contrasting dark wood.

Ornamental iridescent veneer of mother-of pearl on an 18th century  bureau-bookcase

Ornamental iridescent veneer of mother-of pearl on an 18th century  bureau-bookcase

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

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

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Sea Creatures in St Fin Barre’s Cathedral

Mosaic of a lobster

In front of the altar of St Fin Barre’s Cathedral in Cork City, Ireland, is a wonderful mosaic floor made by craftsmen from Udine in the north-east of Italy, using marble from the Pyrenees. The mosaic represents a vision of heaven as described by St Matthew, likening it to a net that has been cast into the sea gathering every kind of creature. Here are a few photographs of the sea creatures depicted.

Mosaic fish

Mosaic fish

Mosaic seashell

Mosaic fish

The mosaic floor before the altar in St Fin Barre's Cathedral

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

At Dogs Bay

Dogs Bay in Connemara has a wonderful white sandy beach composed of the tiny shells of microscopic one-celled creatures that live mostly on the mud of the ocean bed. These animals are called Foraminifera. When they die, millions upon millions of their calcium skeletons, bearing many chambers and holes, and not visible to the naked eye, wash ashore to form this unusual sand. This is such a rare occurrence that Dogs Bay beach is the only one composed of foraminifera in the northern hemisphere.

The bedrock of the land around this wonderful white sandy shore is made up of volcanic rocks including granite that has many different colour forms and patterns due to the different mineral crystals that it contains – if you get up really close to see it. The granite outcrops on the shores often have a rounded surface where ice sheets or glaciers passing over them have ground them smooth. The waterside rocks form attachments for a variety of seaweeds, along with many seashore creatures, particularly gastropod molluscs like periwinkles and limpets, whose brightly-coloured empty shells accumulate at the base of boulders low down in the intertidal zone.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Striped shells from Studland

Striped seashells on a plate

Pictures of some seashells in a dish on my windowsill. I picked them up on the strandline at Studland Bay when I last visited because I liked the striped patterns. I think the concentric darker bands reflect the slower winter growth of the living mollusc while buried in deeper, mainly oxygen-poor, sediments offshore. This is where anaerobic bacteria thrive and their sulphur-rich waste products stain objects black.

Hayward (1994) says of this deeper sandy layer:

Below the boundary the black sand is essentially anoxic; free oxygen is totally absent, and the microfauna must survive through anaerobic processes. Bacteria still thrive but in the absence of oxygen use fermentation, or other chemosynthetic processes, to break down organic compounds. Many bacteria reduce sulphate, nitrate or carbonate ions to produce hydrogen sulphide. ammonia or methane, which give black sand the same unpleasant smell as sticky estuarine muds. The hydrogen sulphide reacts with iron in the sand to give black iron sulphides; as these are gradually carried to the surface by burrowing animals they are oxidised to ferric oxide, which imparts the yellow colour characteristic of the upper layers.

REFERENCE

Hayward, Peter J. (1994) Animals of sandy shores, Naturalists’ Handbooks 21, Richmond Publishing, page 10, ISBN 0 85546 293 0

A heap of striped bivalve shells

Close-up of striped seashells from Studland

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Ringstead Bay Fossil Bivalve – Ctenostreon proboscideum

Most of the examples of this fossil bivalve, Ctenostreon proboscideum, were partial specimens embedded in the rocks at Ringstead Bay in Dorset, England. However, the large strongly-ribbed shell is unmistakable and easily recognised in the many boulders on the beach at the west end of the bay – at least they were easily seen when the pebbles had all been washed away after the storms. The photographs in the gallery above show Ctenostreon shells as they were found on the beach last week. The boulders had fallen from the Ringstead Coral Bed which is a narrow layer,  packed with fossils, of no more than 30 centimetres depth, and which can be seen in short lengths in the vertical section through the strata at the top of the beach.

The almost complete fossil specimen shown with the blue background (photographed at home) was found many years ago after similar severe weather. You can see that the two valves are still together and the space between them filled with marly limestone material, indicating that the original animal was already dead, with the two shells gaping open, when it was buried under new sediments.

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Common Piddocks – rock-boring molluscs

Common Piddock dorsal view

Here are some close-up photographs of the Common Piddock – Pholas dactylus Linnaeus (Mollusca; Bivalvia; Pholadacea; Pholadidae) showing details that are important for its specific identification. The specimen in the first three images still has the dead animal within the shells. This is one that I collected from those I found at Monmouth Beach in Lyme Regis (see the previous post) where a slab of shale, complete with the rock-boring molluscs still inside the burrows, had been thrown up on the shore by stormy seas. The empty shell shown in images 4 – 8 is a beach-worn specimen picked up on Knoll Beach at Studland a few weeks ago.

Although the length of the shell of the Common Piddock can be up to 15 – 24 cm or 6 inches, the examples shown here are smaller – with an  actual size of shell for the Monmouth Beach specimen of 50mm, and 108 mm in the shell from Knoll Beach.

Full details of the shell characters used for identification can be found in the references given below. This bivalve mollusc bores into sand, peat, marl, wood, shale, slate, chalk, limestone, red sandstone, schists, firm clays, and even thick old oyster shells, from low on the seashore to depths of a few fathoms. It occurs in The British Isles from Kent along the south and south-west coasts, including South Wales, and as far south as the Atlantic coast of Morocco. Of particular interest is the phenomena of phosphorescence or luminescence exhibited by the living animal which has has bioluminescent properties and glows with a blue-green light in the dark.

Earlier posts on Jessica’s Nature Blog that refer to the holes in rocks and pebbles made by piddocks and other seashore creatures include:

Rocks with holes made by Piddocks – Part 1

Beach Stones with Holes at Worms Head Causeway

Peat ‘pebbles’ with piddock holes

Pebbles with holes made by boring sponges

Pebbles with holes made by tube worms

Pebbles with holes made by sea creatures

Driftwood with holes made by Gribbles & Shipworms

Benjamin & the pebble full of holes

Shells with holes made by boring bivalves

A rocky beach near Portland Bill

REFERENCES

Tebble, Norman (1966) British Bivalve Seashells – A Handbook for Identification, published for the Royal Scottish Museum by HMSO – Edinburgh, 2nd Edition 1976, ISBn 0 11 491401 X, pp 175 – 180. [Out of print but now available on CD from Pisces Conservation Ltd.]

Hayward, P. J., & Ryland, J. S. (Eds.) (1995) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, 1998 reprint, ISBN 0 19 854055 8 (Pbk), pp 619 – 622. Still in print and available from Amazon and other booksellers.

MarLIN about Pholas dactylus

Wikipedia about Pholas dactylus

World Register of Marine Species about Pholas dactylus

Marine Species Identification Portal – about Pholas dactylus

Common Piddock right side view

Common Piddock ventral view

Common Piddock exterior view left valve

Common Piddock exterior view left valve

Common Piddock anterior end left valve

Common Piddock interior view left valve

Common Piddock shell showing umbonal reflection

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved

Rocks with holes made by Piddocks – Part 1

It is common to find pebbles and rocks which have holes in them when you walk on the seashore. These holes are frequently the result of various marine invertebrates that have burrowed into the rock. The larger, nearly round, holes about a centimetre or so across are often made by bivalved molluscs called Piddocks – these have a special shells and processes for mechanically boring into the rock.

Most commonly, you find stones, or shells, or bedrock, with holes – but the inhabitants have long disappeared. Other times, you glimpse the shell within the burrow but removing it is very difficult to do without totally destroying the shell. If you are really lucky, then you might spot a colony of living piddocks in their burrows at the lowest point of the tide where they will be sporadically squirting water out of their protruding siphons.

In any event, it is quite difficult to see all the details of the shells and thereby identify the creatures to species. Shells that occasionally get washed up on the beach may be abraded and worn, and vital parts for identification are always missing. So, I was delighted last Sunday to see slabs of broken shale, complete with piddocks in burrows (albeit dead specimens), washed up on the shingle of Monmouth Beach in Lyme Regis which is in Dorset, England.

This provided a wonderful opportunity to see what these boring bivalve molluscs and their shells really look like and observe the particular shell features that adapt the organism for this strange lifestyle – but which are normally missing from beach worn specimens on the strand-line.

As far as I can make out, all the specimens that I photographed on the beach were the Common Piddock (Pholas dactylus). I took a few home to clean them up and photograph them in better conditions. The light at the time was very poor, winds were very strong making it a problem to keep the camera still, and the air was laden with salty moisture that persistently misted the camera lens. I’ll show the photographs I took at home in the next post. Meanwhile this post will focus on the piddock shells in situ.

The shell of the Common Piddock is elongate, roughly elliptical and can grow up to 150 mm long – although the specimens I saw were a lot smaller. The anterior (front end) of the shell has a strange beaked appearance and surrounds a permanent pedal gape through which the muscular foot can be extended. The surface sculpturing at the front end of the shells consists of many short, sharp spines that develop at the junctions where the concentric ridges of the valves intersect with the radiating ribs. The spines enable the mollusc to use the shell like a rasp to file away the rock (or shell, or wood, or peat) as it bores down and creates its personalised living accommodation within the protective confines of the substrate.

This boring mechanism is aided by several extra features of the shell – accessory plates on the outside and a long curved process called the apophysis on the inside. The external accessory plates are the paired protoplax, the paired mesoplax, and the single metaplax. Rhythmic contractions of the muscles attached to these plates, and to the apophysis, enable the mollusc to perform a twisting action that aids the drilling process. The whole procedure is further enhanced by a forcing outwards of the two valves against the rock walls using hydrostatic pressure (sucking water in through the siphon and holding it  temporarily to create pressure).

COPYRIGHT JESSICA WINDER 2014

All Rights Reserved