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

Abstract

A classification of the entire Phylum Nematoda is presented, based on current molecular, developmental and morphological evidence. The classification reflects the evolutionary relationships within the phylum, as well as significant areas of uncertainty, particularly related to the early evolution of nematodes. It includes 3 classes, 8 subclasses, 12 superorders, 32 orders, 53 suborders, 101 superfamilies, 276 families, 511 subfamilies, 3030 genera, and 28537 species. All valid species named from the time of publication of the previous classification and census (2010) to the end of 2019 are listed, along with the number of valid species in each genus. Taxonomic authorities are provided for taxon names of all ranks. The habitats where the species in each genus are found are listed, and an alphabetic index of genus names is provided. The systematics of nematodes is reviewed, along with a history of nematode classification; evolutionary affinities and origins of nematodes; and the current diagnosis of the group. Short overviews of the general biology, ecology, scientific and economic importance of the group are presented.

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

“…Their huge numbers and potential range of foods means that they can be of great ecological importance in many situations for ecosystem function (Adams & Wall 2000, Bardgett & Griffiths 1997, Barker & Koenning 1998, Bonkowski et al 2000, Hodda 2009a, Ingham et al 1985, Majdi & Traunspurger 2015, Nicol et al 2011, Petersen & Luxton 1985, Shakya & Yadav 2020, Singh et al 2013, Trap et al 2016). However, nematodes' great taxonomic and ecological diversity, together with the fact that they are mostly small and hard to identify, has meant that most species are still uncollected and undescribed (Hodda 2007, 2022a, Hugot et al 2001, Lambshead 1993). This, in turn, has meant that interpreting the likely impact of nematodes in most situations is problematic-and, as stated above, nematodes are found in large numbers in just about all situations on earth.…”

“…The trophic groups for all valid genera from the most recent comprehensive classification of nematodes are listed, and the basis for the allocation of each genus is discussed. The genera are listed alphabetically, which should enable classification into a probable trophic group of any nematodedescribed or undescribed-provided there is either an identification to genus, some morphological information, or else some information on likely phylogenetic affinities (when read in conjunction with the comprehensive phylogenetic classification (Hodda 2022a)).…”

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

“…The new classification and census adds about 3800 new species in over 300 new genera, including fossil species as well (Hodda 2011, Hodda 2022a.…”

“…They are very diverse, with nearly 30,000 species described so that keeping track of the classification of the entire phylum is a substantial task: Nematoda is the phylum with 5 th most described species, less than Arthropoda, Mollusca, Craniata and just less than Platyhelminthes, but more than Echinodermata, Annelida and Cnidaria (Hodda 2022a, Zhang 2011. Not only are there many species described, but there are probably a much larger number undescribed: even the lowest estimates of total nematode species numbers start at half a million species, and the highest estimates are more than 10 million species (Hodda 2022a). They are also mostly small, cryptic and morphologically simple, meaning that diagnosis by traditional morphological characters is often hard.…”

“…The original construction and more recent update of a comprehensive classification and census of all valid species and genera of nematodes (Hodda 2007(Hodda , 2011(Hodda , 2022a has afforded the opportunity to examine trends in nematode systematics, and the nature of the challenges they reveal. Common trends and issues in nematode systematics emerging from the review of several thousand taxonomic publications are examined.…”