SYMBIOSIS BETWEEN SERPULID POLYCHAETES AND HYDROID CNIDARIANS: 187 MILLION YEARS OF BIOTIC INTERACTION

Embedment fossils – bioclaustrations – provide unequivocal evidence of biotic interactions in the geological past. Calcareous tubes of serpulid worms containing numerous tiny holes with raised rims have been known for almost 200 years. However, these bioclaustrations were not named formally until 1901 when Rovereto described examples infesting the serpulid Protula in the Pliocene of Italy and introduced the genus Protulophila. After studying the morphology of Protulophila in detail, including the network of zooids beneath the surface of the serpulid tubes, Scrutton (1975) inferred that Protulophila was a hydroid cnidarian. The discovery of modern examples of Protulophila in the Red Sea, Madagascar, Philippines, Indonesia, New Caledonia and New Zealand shows that Scrutton was correct. A molecular sequence obtained from a New Zealand sample shows the Protulophila animal is definitely a hydroid but cannot be matched any published sequences for either medusoid or free-living polypoid stages of these animals. The fossil record of Protulophila can be traced back to the Pliensbachian stage of the Early Jurassic. A wide diversity of fossil serpulid genera have been found infested by Protulophila, particularly in the Jurassic and Cretaceous of northern Europe. Ecological and evolutionary questions that can be asked of this symbiosis include: (1) how do the living symbionts interact and what advantages and disadvantages do they incur? (2) have infestation rates changed through time? (3) what evidence is there for species diversity among the Protulophila-producing hydroids? (4) have there been changes in habitat occupancy and biogeographical distribution through time?