Phylum Annelida
Class Polychaeta
Family Serpulidae
Common names: serpulid worms
Overview
Serpulidae is a large, mostly marine, family of sedentary polychaetes inhabiting calcareous tubes. They are characterised by a branchial crown which is a feather-like feeding and respiratory structure comprising radioles (branches) that are attached basally to a lobe surrounding the mouth. The body is distinctly separated into thoracic and abdominal regions and possesses a thoracic membrane (a thin fold extending from the dorsal part of the collar to the ventral side of the posterior thorax), although its development varies between species. A modified radiole (primary branch of the branchial crown) that serves as a tube plug (operculum) when a worm withdraws into its tube, is generally present, but is absent in some species or is fragile and often missing in preserved specimens. Setae may be smooth and simple (capillaries) or hook-like with a dentate (toothed) tip (uncini). All serpulids build hard tubes of crystalline calcium carbonate and a mucopolysaccharide matrix using calcium glands located on the collar. Serpulids are often very brightly coloured with distinctive eye spots however, colour is rapidly lost in preserved specimens.
Distribution and diversity
Serpulidae is an almost totally marine family comprising over 400 species in 80 genera worldwide, with around 90 species and 36 genera known from Australian waters. Only one species, Marifugia cavatica, truly inhabits freshwater, occurring in ground waters of the Dinaric karst across Bosnia and Herzegovina, Croatia and Slovenia to north-eastern Italy. Five other serpulid species, comprising the genus Ficopomatus, are found in brackish habitats worldwide. Two cosmopolitan Ficopomatus species occur in Australia: F. uschakovi and F. enigmaticus (a cryptogenic species whose origin is unclear).
Life cycle
Serpulidae reproduce both sexually and asexually, and many are capable of both. Asexual reproduction occurs by budding of the posterior end of the worm (paratomy). In sexual reproduction, fertilisation is external, either with sperm and eggs broadcast freely in the water or released into the water of the tube. The larvae of some species are planktotrophic (feed on plankton) or lecithotrophic (generally do not feed, relying on yolk in egg). Others are known to brood larvae either freely in the tube, in calcareous brooding pouches outside the tube, attached to the branchial crown or in pouches in the thoracic membrane. Reproduction in Ficopomatus enigmaticus (broadcast spawning and a pelagic larva) is limited to periods of higher salinity; otherwise freshwater populations are maintained by recruitment of osmoregulating adults from more saline waters.
Feeding
It is thought that serpulids are suspension feeders using their crown of tentacles (which are homologous to palps of other polychaetes), but there have been few studies of feeding in the family.
Ecology
The vast majority of serpulids are marine, occurring widely from tropical to polar regions and from the intertidal to the deep sea and are almost always associated with hard substrates, especially rock, but may also occur attached to piers, mollusc shells, the carapaces of decapod crustaceans, seagrasses, algae and jetsam. The European Marifugia cavatica, unique in being the world's only described freshwater serpulid, inhabits subterranean freshwater in caves. Ficopomatus occur in brackish habitats with fluctuating salinities, such as coastal lakes, lagoons and estuaries, attached to shells, rocks and decomposing leaves.
Ficopomatus sp.
Image credit: � Andrew Bould, used with permission.
Collector: Rob Morecroft
