Biological diversity, or biodiversity, is the variety of life: the different plants, animals and micro-organisms, their genes and the ecosystems of which they are a part.   For the importance of biodiversity and its study, please read this essay by E.O. Wilson.

Nematomorph Diversity

To date, approximately 300 species of nematomorphs have been described. The majority occur in freshwater and five species live in the sea. Since the 1990s, about 75 new species have been described. Most new species were described from Argentina, the nematomorph fauna of which was already comparatively well studied. New species have also been found in Europe and North America, which are densely sampled regions. This shows that even in the better sampled regions, the biodiversity of Nematomorpha is not completely known.

Gordiids

Currently, three hundred species have been described in 19 genera (Hanelt, 2004); 56 of these since 1990. Between 1758 (genus Gordius) and 1965 (genus Dacochordodes) 22 genera of freshwater Nematomorpha (Gordiida). In 1999, a prehistoric genus (15-45 MYA) was added containing the species Paleochordodes protus, found emerging from a cockroach trapped in amber (Poinar, 1999). The genus, Noteochordodes, was added in 2000 (de Miralles and de Villalobos, 2000). Besides the description of new species, several species were reinvestigated during the past years, in combination with a critical evaluation of the validity of genera. A reinvestigation of Chordodiolus echinatus revealed that this species, the only representative of the genus Chordodiolus, belongs into the genus Beatogordius (Schmidt-Rhaesa, 2001b; Schmidt- Rhaesa and Ehrmann, 2001).   In addition,  the genera Pantachordodes and Dacochordodes have recently been synonymized.

Schmidt-Rhaesa (2001a) suspected that several other genera, which include one or very few species are invalid, and synonyms to other genera. Unpublished results confirm this for the genera Pantacordodes (with the only species P. europaeus (Heinze, 1952)) and Dacochordodes (with D. bacescui (Capuse, 1966)) which both belong to the genus Spinochordodes (Zanca & Schmidt-Rhaesa, unpublished results).  Most gordiid descriptions have come from few very well-sampled areas, such as Europe, Argentina and central Africa, although even in these regions, our knowledge of nematomorph biodiversity remains incomplete (Hanelt, 2004). Focusing on these better studied areas, it appears that nematomorph species richness varies greatly between geographic areas (Table 1; also see Fig. 3). 

For example, Europe contains roughly 100 described species whereas the United States contains only 14 in a roughly comparably-sized area. A difference in sampling effort likely does not explain these differences entirely. A rough estimate of expected global diversity can be calculated from these data: average number species (of areas listed in Table 1) per 1 million km2 is 12.8; there is149 million km2 of land area on earth (subtracting desert, ice-locked areas, etc); leading to an estimate of 1,900 species globally, suggesting that less than 16% of gordiid species have so far been described. Though tentative these calculations clearly indicate that much work remains especially in several severely understudied areas

To learn more, visit this wikispecies entry.

Nectonematids

Very little is know about nectonematids, or marine hairworms.  Our best guess is that five species have been properly described from a single genus, Nectonema.  However, since so little research has been done on this group, this is just a guess.

The species that have been described are: N. agile, N. melanocephalum, N. munidae, N. svensksundi, N. zealandica.

To learn more, visit this wikispecies entry.