Phylum Nematoda: trends in species descriptions, the documentation of diversity, systematics, and the species concept

Abstract

This paper summarizes the trends in nematode species description and systematics emerging from a comparison of the latest comprehensive classification and census of Phylum Nematoda (Hodda 2022a, b) with earlier classifications (listed in Hodda 2007). It also offers some general observations on trends in nematode systematics emerging from the review of the voluminous literature used to produce the classification. The trends in nematodes can be compared with developments in the systematics of other organisms to shed light on many of the general issues confronting systematists now and into the future.

Phylum Nematoda: a classification, catalogue and index of valid genera, with a census of valid species

“…This is less than 0.1% of the estimated total number of species, but 1.5% of the number of known, described species (Hodda 2022a). What it means is that around 13% or an eighth of described species have been described in the last 10 years (Hodda 2022a).…”

“…Exactly how many nematode species there are is not definitively known. The smallest estimate of total number of nematode species is half a million, while the largest is 20 times that-10 million species (Grassle 1989, Grassle & Maciolek 1992, Hodda 2022a, Hodda & Khudhir 2022, Hugot et al 2001, Lambshead 1993, Lambshead & Boucher 2003, May 1988, Stork 1993). The extreme variance in these estimates shows how little is definitively known about nematode species.…”

“…Estimates of the proportion of nematode species known vary from much less than 1% to around 5%, making them among the least described taxa, and certainly the least described of the mega-diverse animal phyla (Andrassy 1999, Hodda 2022a). Progress in describing nematode species has been slow, but the rate of descriptions is increasing slowly to the current rate of about 400 species per year (Hodda 2022a). This is less than 0.1% of the estimated total number of species, but 1.5% of the number of known, described species (Hodda 2022a).…”

“…Progress in describing nematode species has been slow, but the rate of descriptions is increasing slowly to the current rate of about 400 species per year (Hodda 2022a). This is less than 0.1% of the estimated total number of species, but 1.5% of the number of known, described species (Hodda 2022a). What it means is that around 13% or an eighth of described species have been described in the last 10 years (Hodda 2022a).…”

Phylum Nematoda: feeding habits for all valid genera using a new, universal scheme encompassing the entire phylum, with descriptions of morphological characteristics of the stoma, a key, and discussion of the evidence for trophic relationships

“…Although some of the schemes for dividing nematodes into trophic groups listed the genera in each group, these were all done many, many years ago (Anderson et al 2009: this being an archival volume of publications originally from 1974to 1983, Boucher 1973, Jensen 1987, Kaya & Gaugler 1993, Wieser 1953, 1959, Yeates et al 1993). Hence these lists lack the many genera described since (Hodda 2022b).…”