Nematoda

Hodda, Mike & Z. - Q, 2007, Phylum Nematoda *, Zootaxa 1668 (1), pp. 265-293 : 271-273

Phylum Nematoda

Many characters have been proposed for diagnosis of the Phylum Nematoda ( Table 1). Morphology, physiology and development have all been used. The diversity within the Phylum, however, has meant that few of these characters are universal within the phylum. Other characters may require substantial studies to determine for even a single species, so they are never likely to be proven for more than a few species. Characters involving developmental processes particularly may be unlikely to be known for any more than a few species. Furthermore, the species studied for these characters may always be skewed to those groups most amenable to study—for example the relatively easily cultured Rhabditida —rather than being a representative sample of nematodes as a whole. Recent evidence has cast some doubt on how universal some of these characters are within the nematodes ( Schierenberg 2005).

1 — characters in bold are considered valid. "1" indicates the feature is considered diagnostic for nematodes.

2 — usually

3 — rarely

4 —in some tissues only

Whether many of the diagnostic characters for nematodes are apomorphic depends as much on the interpretation of the characters in other phyla as it does on interpretation of the character within the nematodes. Recent phylogenies based on molecular evidence have also cast doubt on what are apomorphic and plesiomorphic characters within the nematodes, and this, too, has implications for what is diagnostic for the Phylum (see below).

There are nevertheless few doubts about what constitutes a nematode, even though the original definition has been modified considerably ( Table 1).