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Biogeography of polychaete worms (Annelida) of the world

Joko Pamungkas*, Christopher J. Glasby, Mark J. Costello

*Corresponding author:

ABSTRACT: The global biogeography of polychaete worms has never been assessed previously. In the present study, we studied the world distribution patterns of polychaetes based on datasets obtained from the Global Biodiversity Information Facility, the Ocean Biogeographic Information System and the authors’ recently published checklist of Indonesian polychaete species. Polychaete biogeographic regions were visualized using ‘Infomap Bioregions’, and the latitudinal species richness gradient of the animals was examined using three metrics, i.e. alpha, gamma and estimated species richness (the last metric was adjusted for sampling bias). We identified 11 major polychaete biogeographic regions. The North Atlantic, Australia and Indonesia were the top three species-rich biogeographic regions in the world. The total polychaete species was higher in the southern hemisphere (about 2100 species, 67 families) than in the northern one (about 1800 species, 75 families) despite significantly more data in the latter (over 500,000 records compared to over 26,000 records). Contrary to the classical idea of a unimodal distribution pattern, the latitudinal gradient of polychaetes was generally bimodal with a pronounced dip north of the Equator (15oN). We suggest the slightly higher peak of species richness in the southern (30oS) than northern (60oN) hemispheres reflects higher southern endemicities. These patterns are unlikely to be due to sampling bias but rather a natural phenomenon, and we found them most significantly correlated with sea temperature.