Nemertina
Geographic patterns

The 97 species of bathypelagic nemertines at present recognised (Gibson, 1995) have mostly been found in off-shore deeper oceanic waters; none has yet been found in shallow bays or in semi-landlocked seas such as the Mediterranean or North Sea, although several individuals have been recovered from nearer-shore locations such as the submarine canyon occurring off Monterey Bay, California (Coe, 1954a) or close to Bermuda (Coe, 1935, 1936).

Ne 3 (Locations in the South Atlantic from where pelagic nemertines have been collected).
The North Atlantic, with representatives from 26 out of the 40 genera (65%), has been investigated more frequently than any oceanic region; 30% of the known species are also known only from the North Atlantic (Ne table1a , Ne table1b), largely due to the publications of Joubin (1906), Brinkmann (1917a, b), Coe (1935, 1936, 1945) and Van der Spoel (1985). North Pacific records, principally by Coe (1926, 1954a) and Korotkevich (1955a), indicate that although the number of genera is less than for the North Atlantic, with only 21 (52.5%) represented, the number of species indigenous to the North Pacific is identical at 30% (Table 1). Collections in the South Pacific and Indian Ocean have yielded 25% and 22.5% of the genera respectively, with similar numbers of indigenous species (9 from the South Pacific, 8 from the Indian Ocean) (Table 1) known only from one or the other region. Many of the bathypelagic nemertines reported from these two oceans are from Antarctic latitudes (Brinkmann, 1920; Wheeler, 1934, 1940; Korotkevich, 1960, 1963, 1964; O'Sullivan, 1983). Representatives of only 6 genera (15%) and 11 species have so far been recovered from the South Atlantic (Ne 3) (Wheeler, 1934; Coe, 1946; Friedrich, 1969b), whilst only a single species and genus is known from the Arctic Ocean (Korotkevich, 1977b) (Ne table1a , Ne table1b).

By far the greater number of bathypelagic species (80%) are known from only one oceanic area (Ne table1a , Ne table1b). Coe (1945, 1946, 1954a, b) argued that, as a consequence of the circulation of deep oceanic currents, pelagic nemertines may over a long period of time be expected to drift from one part of the world to another and thus possess wide zoogeographic distributions. The recorded data on these animals does not, however, support Coe's hypothesis; very few species are known from more than a single oceanic region (Ne table1a , Ne table1b) and of the 6 (6.2%) the most widespread form appears to be Pelagonemertes rollestoni. Van der Spoel (1983) believes that there are comparatively few planktonic taxa with a widespread zoogeographic distribution and other authors, such as Van der Spoel and Heyman (1983), have shown that significant proportions of the bathypelagic fauna from one oceanic area or another relate to endemic taxa. With so many of the pelagic nemertines known from only single or, at best, a small number of specimens, identifications of conspecific forms from widely separated geographic regions, such as Dinonemertes investigatoris from the North Atlantic and Indian Ocean, must be open to uncertainty. Among all the reported bathypelagic nemertines one species, Nectonemertes mirabilis, appears to be by far the most common and abundant (Coe, 1954a). More than 400 specimens of this species have now been collected; Brinkmann (1917a), for example, reported a total of 117 individuals collected by expeditions in the North Atlantic, Coe (1945) listed 44 specimens from the Bermuda area and Van der Spoel (1985) found 248 examples in collections made by the AMNAPE cruises.