Actinonema Cobb, 1920

Venekey, Virag, Gheller, Paula F., Kandratavicius, Noelia, Cunha, Beatriz Pereira, Vilas-Boas, Ana Carolina, Fonseca, Gustavo & Maria, Tatiana F., 2019, 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, Zootaxa 4578 (1), pp. 1-67 : 21-22

Genus Actinonema Cobb, 1920

The genus Actinonema was proposed by Cobb (1920) with the description of A. pachydermatum . Wieser (1954) synonymized Pareuchromadora Schuurmans Stekhoven & Adam, 1931 with Actinonema transferring all species ( P. amphidiscatum Schuurmans Stekhoven & Adam, 1931 ; P. fragile sensu Allgén, 1942 ; P. longicaudatum Chitwood, 1951 and P. setifer Schuurmans Stekhoven, 1943 ). Wieser (1954) also transferred Spiliphera fragilis described by Allgén (1929) to Actinonema and synonymized P. amphidiscatum with it. Furthermore, Wieser (1954) transferred Euchromadora longicaudata described by Steiner (1918) to Actinonema and synonymized the recently transferred P. fragile and P. setifer with it. In order to avoid homonymy of P. longicaudatum with E. longicaudata, Wieser (1954) renamed the first to A. chitwoodi but this species should be considered species inquirendum since the description was based only on a poorly described single female. Later A. fragile , mentioned as Spiliphera fragilis , was synonymized with A. pachydermatum by Lorenzen (1972). The species A. fidatum , A. celtica and A. grafi were described by Vitiello (1970), Boucher (1976) and Jensen (1991), respectively. Muthumbi & Vincx (1998b) described A. paraceltica and A. smolae and also discussed differences between Actinonema and the closely related genus Rhips . The authors state that two main characters are considered to distinguish Actinonema and Rhips in the majority of identification works: cuticle with solid cones in Rhips (absence of the same in Actinonema ) and double-jointed spicules in Rhips (simple spicules in Actinonema ). However, Muthumbi & Vincx (1998b) affirm that sometimes is difficult to assign the correct genus because males of Rhips can lose their spicules. Therefore, we agree with them that solution for a correct identification can come only at molecular level and in mixed populations of Actinonema and Rhips the individuals should be treated as one single ecological unit. The last addition to Actinonema was by Shi et al. (2018), who described A. falciforme and also presented an identification key for the species in this genus.

Diagnosis (modified from Muthumbi & Vincx 1986b and Tchesunov 2014): Cuticle heterogenous with lateral differentiation as a ridge beginning at the end of the pharynx. Six outer labial and four cephalic setae arranged in one circle of ten setae. Amphideal fovea conspicuous, transversally oval with a double contour. Buccal cavity with one small dorsal tooth and two ventrosublateral teeth. Posterior pharyngeal bulb may be developed or not. Spicules simple and curved. Gubernaculum with L-shaped pieces.

Number of valid species: 8.

Genus Actinonema Cobb, 1920

Syn. Adeuchromadora Boucher & De Bovée, 1971

Pareuchromadora Schuurmans Stekhoven & Adam, 1931

VALID SPECIES

1. Actinonema celtica Boucher, 1976 (West Channel)

2. Actinonema falciforme Shi, Yu & Xu, 2018 (East China Sea)

3. Actinonema fidatum Vitiello, 1970 (Mediterranean)

4. Actinonema grafi Jensen, 1991 (Norwegian Sea)

5. Actinonema longicaudatum ( Steiner, 1918) Wieser, 1954 (SW Africa)

Syn. Actinonema setifer ( Schuurmans Stekhoven, 1943) Wieser, 1954

Euchromadora longicaudata Steiner, 1918

Pareuchromadora fragilis sensu Allgén, 1942

Pareuchromadora setifer Schuurmans Stekhoven, 1943

6. Actinonema pachydermatum Cobb, 1920 (Florida)

Syn. Actinonema amphidiscatum ( Schuurmans Stekhoven & Adam, 1931) Wieser, 1954

Actinonema fragile (Allgén, 1929) Wieser, 1954

Adeuchromadora megamphida Boucher & De Bovée, 1971

Pareuchromadora amphidiscata Schuurmans Stekhoven & Adam, 1933

Spiliphera fragilis Allgén, 1929

7. Actinonema paraceltica Muthumbi & Vincx, 1998 (Indian Ocean)

8. Actinonema smolae Muthumbi & Vincx, 1998 (Indian Ocean)

SPECIES INQUIRENDUM

1. Actinonema chitwoodi Wieser, 1954 (Texas, USA)