Antranig Basman, Charlie Gibbs, Donna Gibbs, Scott Gilmore, Andy Lamb, Andrew Simon
August 7th, 2023
Galiano Island’s horseshoe worm diversity
‘Phoronida’ is the plural form of the phylum’s type genus Phoronis, likely derived from the Latin ‘Phoronis’ (the last name of the mythical Io, priestess of Argos).
Phoronida (horseshoe worms) are a small phylum of soft-bodied filter-feeding marine animals that form upright tubes of chiton to support their bodies. Worldwide the phylum includes two genera, comprising 13 recognised species. Six species are reported for the Northeast Pacific (Carlton 2007), of which one species is known locally: Phoronis ijimai.
Phoronids are called “horseshoe worms” because the top of their worm-like body contains rows of ciliated tentacles forming a horseshoe shape. This is the lophophore—the feeding organ they share in common with the Brachiopoda, Bryozoa and Entoprocta.
The horseshoe worm Phoronis ijimai – Photograph by Karolle Wall
Community science contributions
Since the Biodiversity Galiano project began in 2016, our community has documented 1 phoronid species in the waters around Galiano Island, confirming all known historical records and adding no new species to the list.
Phoronids are benthic organisms that occur at depths ranging from the intertidal zone to about 400 m of depth in all oceans and seas throughout the world, except the Antarctic seas. Their larvae are pelagic and feed on plankton, sometimes comprising a large proportion of zooplanktonic biomass. Of the six species reported for the region, it is uncertain which may be expected to occur around Galiano Island, though Phoronopsis harmeri has been reported nearby from the Saanich Inlet (RBCM 976-01136-010). Collections are sparse for this understudied phylum and much doubt surrounds the taxonomy and distributional ecology of the regional fauna. Keys are based on fully developed larval stages, so investigations into this phylum generally entail raising larvae to advanced stages so that they can be reliably compared to illustrations for identification. Even then, their determination is usually based on internal anatomy, which often can only be gleaned by examining microscopically thin sections. Given the challenges associated with this group, most collections at the Royal British Columbia Museum remain unidentified.
Top community contributions to our knowledge of Galiano Island’s bryozoan diversity
Here, you can browse photos of mammal species commonly documented around Galiano Island, as well as recent observations, most favourited observations, and top observers, based on iNaturalist data. Please help contribute to the growing record of the island bryozoan diversity by submitting your observations to the Biodiversity Galiano iNaturalist project.