A census of deep-water sipunculans (Sipuncula)

摘要

The Sipuncula, or peanut worms, are a small taxon of lophotrochozoan worms that live mostly in warm shallow waters, but little is known about the diversity and distribution of this group in the deeper parts of the ocean (& 2000 m). To address this point, all existing information from the scientific literature on deep-water sipunculans was retrieved, and a census was organised in several data matrices by species and by geographic and bathymetric distribution. From this data, deep-water sipunculan fauna were found to include representatives of 4 families, 10 genera, 51 species and 3 subspecies. Geographical range maps for all the censused species were created. The most ubiquitous species are Nephasoma diaphanes (Gerould, 1913); Phascolion lutense Selenka, 1885; Golfingia muricaudata (Southern, 1913); Apionsoma murinae (Cutler, 1969), G. margaritacea (Sars, 1851) and Onchnesoma magnibathum Cutler, 1969. By contrast, 18 species of various genera in the dataset are considered to be extremely rare, with only one previous record. No endemic species have been detected on the sea bottoms investigated to date. With regard to vertical distribution, most deep-water sipunculans were collected at depths ranging from 2500 to 3000 m, whereas there were fewer ultra-abyssal and hadal records (& 6500 m). This also applies to the deepest depths investigated (& 7000 m), where only three isolated records of three different species (N. diaphanes, P. lutense and P. pacificum Murina, 1957) were found. By relating species richness to depth, a significant linear regression was found, with lower richness values at greater depths. Finally, attempts to relate the species richness values to latitudinal or longitudinal gradients have as yet proved unsuccessful. The conclusion drawn from this census is that sipunculan fauna down to a depth of 2000 m is characterised as remarkably sensitive to bathymetry, with the lowest species richness values recorded in the deeper bottoms.