Calcareous worm tubes on Flat Oyster shells

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P1090452aBlog1 Calcareous tubes made by marine worms, like Pomatoceros species, on specimens of archaeological oyster shells (1). 

Calcareous tubes are one of the most common types of encrustation on shells, stones, and flotsam at the seashore. These are made by small marine worms of the Serpulidae family. Unlike the the Polydora type marine worms mentioned in earlier posts, which create burrows and tunnels in the actual matrix of shells and stones, adult worms such as Pomatoceros triqueter and Hydroides norvegica cement the chalky tubes they occupy onto the surface of the substrate.

Pomatoceros is one of the types of organism frequently responsible for worm tubes on seashore objects in the UK. The tube has a distinct almost triangular cross-section. Along the length of the tube is a clear sharp ridge or keel. There is a single central one in Pomatoceros triqueter (Linnaeus) but in P. lamarcki (Quatrefages)  there are two vestigial longitudinal ridges laterally placed on each side of the median keel. The tubes can be found as single and scattered specimens, or as tangled knots and heaps with the tubes in various orientations.

The Pomatoceros tubes zig-zag across the surface of the shell. From a distance it looks as if someone has been scribbling with a white marker. The vague resemblance of the tubes to Gothic writing script has given them the common name of “German Writing” .

Another type of distinctly-shaped chalky tube is made by the worm Hydroides norvegica (Gunnerus) or other species in that genus.  [I have found these tubes less frequently than Pomatoceros and only have the photograph above to illustrate them in this posting]. These tubes are circular in cross-section (contrasting with the triangular shape in Pomatoceros). There is no keel and the tube is un-ornamented except for the visible growth lines. The tubes are irregularly coiled in one plane or occur in masses of tubes lying parallel to each other and with the openings all facing the same direction.

The photographs in this posting show a variety of these calcareous tubes on European Flat Oyster shells – Ostrea edulis Linnaeus – from a selection of UK locations. The ones in the top picture are on archaeological shells. Some of the recent or modern specimens (shown below) were found on the seashore and others were dredged fresh and alive from natural deep water oyster beds.

For more information about European Flat Oyster shells in Jessica’s Nature Blog, search in the OYSTER VARIATIONS category. 

Calcareous tubes of the marine worm genus Pomatoceros encrusting the outer surface of a modern Flat Oyster shell from a Gower beach, West Glamorgan, UK (2)  

Calcareous tubes of the marine worm genus Pomatoceros encrusting the inner surface of a modern Flat Oyster shell from a Gower beach, West Glamorgan, UK (3)

P1160821Blog4 Detail of encrusting calcareous tubes of the marine worm genus Pomatoceros on the surface of a modern Flat Oyster shell from a Gower beach, West Glamorgan, UK (4)

P1060824Blog5 Calcareous tubes of the marine worm genus Pomatoceros cemented to the inner surface of a modern burial-blackened European Flat Oyster shell from Rhossili, Gower, West Glamorgan. UK (5) 

P1060825Blog6 Detail of calcareous tubes of the marine worm genus Pomatoceros cemented to the inner surface of a modern burial-blackened European Flat Oyster shell from Rhossili, Gower, West Glamorgan, UK (6)

P1090029Blog7 Calcareous tubes of the marine worm genus Pomatoceros cemented to the outer surface of a dredged modern European Flat Oyster shell from The Solent, Hampshire, UK (7) 

P1090032Blog8 Detail of calcareous tubes of the marine worm genus Pomatoceros cemented to the outer surface of a dredged modern European Flat Oyster shell from The Solent, Hampshire, UK (8) 

 

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