Food for the bubble shell Hydatina physis?

Dear Ian,
Years ago I looked at the stomach contents of H. physis from various localities around the world, as well as other related species, and in all cases the worm remains were easily identified as belonging to the Cirratulinae, a subfamily of the Cirratulinidae. Over the years I have checked the odd stomach and again have only found similar worms, suggesting they are fairly specific feeders.

However as Marphysa would be a lot easier to collect, I guess anything is worth a go. I remember keeping a new Zealand species of worm-eating aglajid, Melanochlamys cylindrica, alive in aquaria for many months on worms that it could not possibly feed on in nature. Species of Melanochlamys feed by rapidly sucking in polychaete worms much like sucking in a long piece of spaghetti. I often found them stuck head down in coralline algae turf, one end of a eunicid or nereid worm in their mouth and the other end desperately trying to escape into a crack or burrow. Collecting nereid worms for them to eat was a time consuming task so on one occasion I decided to test them on Sabellaria kaiparaensis, a worm which builds a tube from sandgrains and clusters in large colonies forming sandy reefs on the shore. Large numbers of worms could be quickly extracted by breaking off sections of the reefs. I would then freeze them in conveniently sized 'ice-blocks' and throw a block into the aquarium every few days where it would melt. The worms would thaw out and the aglajids would eat them with great enthusiasm. It seems in that case the aglajids were eating certain worms on the shore, not so much from choice, but because they were able to catch them.

It is possible with Hydatina that it eats cirratulid worms because they are relatively easy to catch in the areas in which it lives. If so then perhaps it would eat other types of worms if they were offered. To have any chance of success though, I suspect they would have to be freshly dead, as alive they would probably move to fast for Hydatina.

For those with no idea about polychaete worms, cirratulids have no head appendages but have long thread-like tentacles along most of the body but especially around the head. They live in crevices, empty burrows or under rocks partially embedded in the sand or mud. They live surrounded by a 'coccoon' of debris, and they extend their tentacles out like the head tentacles of terebellid worms, to collect food particles. On the other hand, eunicid worms like Marphysa, although living in burrows, are quite active worms emerging either partially or fully from their burrow to feed on carrion, or in some cases, algae.

Ian, if your enquirer has any success with Marphysa, I would be interested to hear about it. Collecting cirratulinid worms would probably be quite difficult and require quite extensive environmental disturbance, turning embedded rocks and digging and scraping around to find them.

Best wishes,
Bill Rudman.