Fossil Facts > Worm Tubes
Not uncommon to find worm tubes adhering to ammonite shells. They need a solid base to attach tubes, on a soft muddy sea floor a shell is a suitable substrate. At Lyme it was noticed that worm tubes seemed to specifically grow on keel of the ammonite shell (pic with red line).
On examination some tubes could be seen between the earlier coils of the ammonite. Ammonite shells are solid – only way the worm could have got there was if it was growing on a living ammonite. It’s thought these worms lived on keel of outer coil of the ammonite (see diagram).
As the ammonite grew and lengthened its shell the worm also extended its tube to maintain its position. The worm fed by filter feeding, partly using the currents formed by the movement of the ammonites shell. The ammonite also kept the worm above the sea floor.
At Lyme, deeper water could often be lacking in oxygen. The most similar thing alive today is a Christmas tree worm. A consequence of this is that as the ammonite grew and added a coil to its shell, it started to grow over the back of the worms tube.
Sometimes the ammonite had an even worse problem as several worms could grow on one ammonite. This caused the ammonite to produce a distorted shell.
Distorted ammonites are not uncommon, and it should be said there are other potential causes of such distortion such as damage to the shell-producing mantle.
The ones in the images all seem likely to be worm caused.
It would be great to end with “and they all lived happily ever after”, but unfortunately that was often not the case…
The worm is a parasite and caused harm to the ammonite in several ways. An ammonite was more likely to die if it had a heavy infestation of encrusting worms.