Mesacanthion ( Filipjev, 1927 ) De Coninck and Schuurmans Stekhoven, 1933

De Souza, João V. & Maria, Tatiana F., 2023, Taxonomic review of Thoracostomopsidae (Nematoda, Enoplida): state of the art, list of valid species and dichotomous keys, Zootaxa 5361 (4), pp. 463-496 : 477-479

publication ID	https://doi.org/ 10.11646/zootaxa.5361.4.2
publication LSID	lsid:zoobank.org:pub:DAB237DC-1444-4007-BCCA-CB92CBE66617
DOI	https://doi.org/10.5281/zenodo.10196925
persistent identifier	https://treatment.plazi.org/id/EA795F35-253C-FFE4-FF27-FF5F53B220C8
treatment provided by	Plazi
scientific name	Mesacanthion ( Filipjev, 1927 ) De Coninck and Schuurmans Stekhoven, 1933
status

Treatment

Genus Mesacanthion ( Filipjev, 1927) De Coninck and Schuurmans Stekhoven, 1933 View in CoL

The genus Mesacanthion was first erected as a subgenus of Enoplolaimus by Filipjev (1927) with the original description of seven species: Mesacanthion banale ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 , Mesacanthion breviseta ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 , Mesacanthion ditlevseni ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 , Mesacanthion karense ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 , Mesacanthion lucifer ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 , Mesacanthion majus ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 , Mesacanthion klugei ( Filipjev, 1927) De Conninck & Schurmans Stekhoven, 1933 and the inclusion of three other species Mesacanthion diplechma ( Southern, 1914) Filipjev, 1927, M. audax and Mesacanthion conicum ( Filipjev, 1918) Filipjev, 1927 , which were previously described as Enoplus and Enoplolaimus (in the case of the last two species). De Coninck and Schuurmans Stekhoven (1933) raised Mesacanthion to genus including all species described by Filipjev (1927) and transfered other six species to it: M. infantile ; Mesacanthion latignathum ( Ditlevsen, 1918) De Coninck and Schuurmans Stekhoven, 1933 ; Mesacanthion microsetosum ( Allgén, 1932) De Coninck and Schuurmans Stekhoven, 1933 ; Mesacanthion oxycephalum ( Ditlevsen, 1926) De Coninck and Schuurmans Stekhoven, 1933 ; Mesacanthion tenuicaudatum ( Ssaweljev, 1912) De Coninck and Schuurmans Stekhoven, 1933 and Mesacanthion virile ( Ditlevsen, 1930) De Coninck and Schuurmans Stekhoven, 1933 . Two decades later, Mesacanthion hirsutum Gerlach, 1953 was described based on a male and a female from Italy.At the same time, a genus review was proposed by Wieser (1953) who considered all species described by Allgén as doubtful, including Mesacanthion primitivum Allgén, 1929 , Mesacanthion gracilisetosum Allgén, 1930 , Mesacanthion paradentatum Allgén, 1932 , Mesacanthion donsitarvae Allgén, 1935 , M. pacificum and M. hawaiiense ; and transfered M. latignathum to Mesacanthoides and M. klugei and M. oxycephalum to Paramesacanthion . This author also described two other species Mesacanthion ungulatum Wieser, 1953 and Mesacanthion longissimesetosum Wieser, 1953 and proposed an identification key for eight of the 14 valid species known at the time. Later, 33 species were considered as valid and six as invalid by Gerlach & Riemann (1974) who also corrected the species epithet to comply with the rules of Latin grammar. Later, eight species were described, and Jeong et al. (2019) did a detailed review of the genus presenting 38 valid species and suggesting two species ( Mesacanthion brachycolle Allgén, 1959 and Mesacanthion ungulatum Wieser, 1953 ) as species inquirendae and nominated one as nomen nudum ( M. microsetosum – here we consider this species as species inquirenda within Paramesacanthion ). These authors also provided a taxonomic key for 22 species with spicules shorter than 2 anal body diameters (abd). The most recent species added to this genus are M. bifidum , Mesacanthion longigubernaculum Lo Russo & Pastor de Ward, 2021 and Mesacanthion sanantoniensis Lo Russo & Pastor de Ward, 2021 , all occurring along the Argentine coast. Here, we consider Mesacanthion arcuatile Wieser, 1959 , M. banale , M. conicum and Mesacanthion cricetoides Wieser, 1959 as species inquirendae because these species present only female descriptions. We also consider M. karense as species inquirenda since it is based on juvenile description, and M. tenuicaudatum because its illustrations are missing in the original description. The given key includes all 36 valid species and it is partially adapted from the one provided by Jeong et al. (2019) which presents only species with spicules smaller than 2 abd.

Diagnosis based in Wieser (1953); Platt & Warwick (1983); Smol et al. 2014 and Jeong et al. (2019): Outer labial and cephalic setae situated at middle or anterior end of cephalic capsule. Mandible well-developed, provided with claws, arch-shaped, consisting of two rod-like columns anteriorly united by a curved bar. Teeth shorter than mandibles. Spicule mostly short, unipartite and symmetrical, sometimes long, bipartite (divided by a seam: M. ditlevseni ) and asymmetrical (anisomorphic and anisometric: M. diplechma ). If long, usually gubernaculum present with caudal apophysis. Marine and freshwater.

Number of valid species: 36

1. Mesacanthion africanthiforme Warwick, 1970a (English Channel)

2. Mesacanthion africanum Gerlach, 1957b (Central Africa)

3. Mesacanthion agubernatus Vitiello, 1971 (Mediterranean)

4. Mesacanthion alexandrinus Nicholas, 1993 ( Lake Alexandrina , South Australia)

5. Mesacanthion arabium Warwick, 1973 (Arabian Sea)

6. Mesacanthion armatum Timm, 1961 (Bay of Bengal, lapsus armatus)

7. Mesacanthion audax ( Ditlevsen, 1918) Filipjev, 1927 (Öresund)

Syn. Enoplolaimus audax Ditlevsen, 1918

8. Mesacanthion bifidum Lo Russo & Pastor de Ward, 2021 (Nuevo Gulf, Argentina)

9. Mesacanthion breviseta ( Filipjev, 1927) De Coninck & Schuurmans Stekhoven, 1933 (Barents Sea)

Syn. Enoplolaimus (Mesacanthion) breviseta Filipjev, 1927