Stones with holes made by Wrinkled Rock Borers (& other seashore creatures)

Scroll down to content

Beach stone with holes made by seashore creatures at Charmouth, Dorset, England.

Beach stones with holes in them excite the curiosity of most people. How did the holes get into the rock? There is no single answer but in many cases the holes in pebbles and beach stones have been made by various seashore creatures including several types of bivalve molluscs, marine worms, and sponges. The same creatures can also make holes in thick old seashells. There are  several earlier posts on Jessica’s Nature Blog describing how the holes are made, by piddocks, for example Pholas dactylus, sponges such as Cliona celata, and polychaete worms like Polydora ciliata and Polydora hoplura. Frequently, there is evidence for more than one type of organism occupying the same stone.

One of the bivalve molluscs that creates holes in stones and thick oyster shells is the Wrinkled Rock Borer Hiatella arctica (Linnaeus). Like the piddock, this species can actively excavate a burrow in soft stone for shelter and protection although unlike the piddock it can attach itself by byssus threads to the outside of solid objects or in cracks and crevices. However, once embedded in the stone it can no longer exit the burrow but obtains all it needs for sustaining life via the tunnel connecting it to the outside world. Wrinkled Rock Borers are smaller than piddocks, measuring no more than 3.8 cms in length when mature. The valves of the shell are thick and robust with distinct furrows, and the leading edges exposed to view in the burrow are rough and straight edged (truncate). Tebble (1966) says that it is not possible to distinguish between the different species of Hiatella in British waters but the descriptions apply to all the species ever recorded here. Hiatella arctica is common around the British Isles from the lower regions of the shore to considerable depths…… It has a wide geographical distribution in the northern hemisphere from the Arctic south through the Atlantic, Mediterranean and Pacific, but the particular limits of its occurrence are not known. It is almost impossible to remove empty Hiatella shells from the excavated holes without breaking them.

Hiatella holes in rock can be secondarily occupied by a similar but smaller bivalved mollusc called Irus irus (Linnaeus). This grows to about 2.5 cms in length. The protruding frill-like concentric ridges on the shell can be very distorted in shape if the shell is occupying a burrow that is too small to allow normal growth. I am not able to discount the possibility that it is Irus shells occupying Hiatella burrows in some of the beach stones illustrated here. Irus (also known as Notirus irus) occurs from low in the littoral zone to a few fathoms.

REFERENCES

Tebble, N (1966) British Bivalve Shells: A Handbook for Identification, published for the Royal Scottish Museum by HMSO, Second Edition 1976, [Hiatella p172-173 & Plate 7h; Notirus p124-125 & Plate 7g].

Hunter, W. R. (1949), The Structure and Behaviour of ‘Hiatella gallicana@ (lamarrck) and ‘H. arctica’ (L.), with special reference to the Boring Habit. Proc. Roy. Soc. Edin. B, 63 III (19): 271-289, 12 figs.

11 Replies to “Stones with holes made by Wrinkled Rock Borers (& other seashore creatures)”

  1. Some years ago, while taking a workshop with a primary school class in weaving, I asked the children if there was anything they could think of that they wouldn’t be able to weave with. One of them said stones. I was quite pleased to be able to produce some examples of stones with holes in from the beach at Lyme Regis. The holes allowed them to be suspended or attached easily to the weaving if not actually woven into the work. Would the stones at Lyme Regis have holes for the same reason as those above?

  2. Stones with holes in them are very common around our coasts, and I have seen beach stones at Lyme Regis with the large regular holes that are made by piddocks.

  3. Lovely informative post, Jessica, and I’ll link it to my own site, as you are much more knowledgeable about the various species of rock-boring mollusc than I am! You found some terrific examples! There is a perpetual fascination for stones with a hole in them. I love them myself (might have, erm, one or two in my coat pocket!) 😀

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s

%d bloggers like this: