Symbiotic polychaetes revisited: an update of the known species and relationships (1998 – 2017)

Abstract

Here we consider the growing knowledge on symbiotic polychaetes since this particular group of worms, and their relationships with their hosts, were reviewed by Martin & Britayev (1998). The current number of symbiotic polychaetes (excluding myzostomids) reported has almost doubled since 1998 (618 versus 373 species) and are now known to be involved in 1626 relationships (966 in 1998), representing 245 and 660 newly reported species and relationships, respectively. Overall, 490 (292 in 1998) species involved in 1229 (713 in 1998) relationships are commensals, and 128 (81 in 1998) involved in 397 (253 in 1998) relationships are parasitic. New commensal and parasitic species and/ or relationships have been respectively reported for eight (Chaetopteridae, Siboglinidae, Fabriciidae, Aphroditidae, Orbiniidae, Pholoididae, Scalibregmatidae, Sigalionidae) and five (Fabriciidae, Typhloscolecidae, Phyllodocidae, Polynoidae, Hesionidae, Serpulidae) polychaete families. Three additional taxa (cephalopod molluscs, gorgonocephalid ophiuroids and ascidian tunicates) are now known to harbour commensal polychaetes, and a further three taxa (decapod crustaceans, chaetognaths and brachiopods) are now known to host parasitic polychaetes. Here we discuss, family by family, the main characteristics and nature of symbiotic polychaetes and their relationships. We conclude that some of the biases identified in 1998 are still uncorrected. Despite the noticeable increase of taxonomic studies describing new species and reporting new relationships, there is still a lack of ecological and biological studies, either descriptive or experimental (e.g. based on behavioural observations of living organisms), addressing the actual nature of the associations. We have also identified that most studies are restricted to a specialised academic world. The next logical step would be to transfer this knowledge to non-specialised audiences. In other words, to contribute to the preservation of our seas, it is our duty to raise awareness of the potential ecological and economic impacts of these symbiotic associations and to allow other eyes to enjoy the intrinsic beauty of symbiotic worms.