The state of the art of Chromadoridae (Nematoda, Chromadorida): a historical review, diagnoses and comments about valid and dubious genera and a list of valid species

Abstract

Chromadoridae is a widespread family of mostly free-living marine nematodes. This systematic review provides for each genus: a historical background, an updated diagnosis and a list of species. Our review recognizes 37 valid genera, 395 valid species, 57 descriptions without enough morphological information for accurate identification (species inquirenda) and 10 species incerta sedis. We also recognize 21 species as nomena nuda. Additionally, polytomous keys were constructed for the subfamilies and for the genera of the three major subfamilies (Chromadorinae, Euchromadorinae and Hypodontolaiminae) using the most important diagnostic characters. A phylogenetic analysis based on rDNA sequences of species available in the GenBank was also conducted. Phylogenetic trees based on the 18S and 28S rDNA confirmed the classification into three subfamilies (Spilipherinae, Hypodontolaiminae and Chromadorinae), despite the absence of defined synapomorphies. Phylogenetic relationships at lower taxonomic level are problematic given the large number of sequences not identified to species level.

Description of a new nematode species, Chromadorina communis sp. nov. (Nematoda, Chromadoridae), from Changdao Island, China and phylogenetic analysis of Chromadorida based on small subunit rRNA gene sequences

“… Chromadora shows a close relationship with Chromadorina in clade A2, and Venekey et al (2019) also noted this and explained this relationship as a result of a misidentification; there are great morphological similarities between Chromadora and Chromadorina ( Venekey et al 2019 ).…”

“… Tchesunov (2014) reviewed the six families of Chromadorida and provided diagnoses of the families and genera; he listed Chromadoridae with five subfamilies and 38 genera, Cyatholaimidae with four subfamilies and 21 genera, Achromadoridae with a single genus ( Achromadora ), Ethmolaimidae with three genera, Neotonchidae with six genera, and Selachinematidae with two subfamilies and 11 genera. Venekey et al (2019) reviewed the family Chromadoridae , provided polytomous identification keys for subfamilies and genera, listed valid species of each genus, and provided a phylogenetic analysis based SSU rRNA gene sequences of 11 genera and large subunit ( LSU ) rRNA gene sequences of eight genera. Phylogenetic relationships within Chromadorida based on full-length sequences of the SSU rRNA gene has been analyzed for 4 families by Holterman et al (2008) and six families (22 genera) by Leduc et al (2017) .…”

Two new species of Hypodontolaiminae (Nematoda, Chromadorida, Chromadoridae) from the Yellow Sea with a phylogenetic analysis in the subfamily

“…(based on Venekey et al 2019 ). Cuticle with homogeneous ornamentation and a pronounced lateral differentiation of two longitudinal rows of enlarged dots.…”

“… Huang and Zhang (2010) described three species from the China Sea, D. major , D. multisetosa , and D. sinica , and provided a short review of Dichromadora . Dichromadora abyssalis was considered as valid by Holovachov (2020) based on the high quality descriptions and illustrations despite not following the International Code of Zoological Nomenclature ( Venekey et al 2019 ). With the addition of D. rigida Thanh, Tu & Gagarin, 2016 and D. agilis Long, Gagarin & Tu, 2022, 35 species are currently considered as valid (based on Venekey et al 2019 ):…”

“… Chromadoridae Filipjev, 1917 is one of the largest families of nematodes and shown as a monophyletic group with synapomorphies of male monorchid with an anterior testis; precloacal supplements cup-shaped or absent but never tubular; females with two reflexed ovaries, anterior to the right of the intestine, posterior to the left of the intestine ( Tchesunov 2014 ). Chromadoridae has been reviewed systematically by Wieser (1954a) , Gerlach and Riemann (1973/1974) , Lorenzen (1981 , 1994 ), Tchesunov (2014) , and Venekey et al (2019) , and its phylogenetic relationships have been analyzed based on rDNA sequences by Holterman et al (2008) , Leduc et al (2017) , Venekey et al (2019) , and Guo et al (2023) . The number of rDNA sequences in Chromadoridae have rapidly increased in GenBank: up to now, 250 sequences from 20 genera of Small Subunit ( SSU ) and 145 sequences from 11 genera of D2–D3 fragment of Large Subunit ( LSU ) have been deposited in GenBank.…”