Spinonema, Larrazábal-Filho & Neres & Silva & Esteves, 2019

Larrazábal-Filho, Alexandre L., Neres, Patrícia F., Silva, Maria Cristina Da & Esteves, André M., 2019, A new genus with three new species of free-living marine nematodes of the subfamily Desmodorinae (Nematoda: Desmodoridae), from the continental shelf off northeastern Brazil, Zootaxa 4615 (2), pp. 321-342 : 323-325

Genus Spinonema gen. n.

Diagnosis. Desmodorinae . Body cylindrical, with well-developed cephalic capsule and short conical tail. Cuticle thick, with vacuoles extending from head capsule to end of tail. Annuli present, extending from head capsule to beginning of tail, structured similarly to those in members of family Epsilonematidae Steiner, 1927 : annuli lack rounded edges, and along the anterior portion of the body the individual annuli slope anteriorly, whereas on the posterior portion of the body the annuli slope posteriorly. Annuli do not overlap with each other. Cuticle also with lateral C-shaped alae on anterior portion of body; these alae are present in both sexes (male and female), varying in size according to species. Dorsal spine present in some species; when present, always located in pharyngeal region. Longitudinal rows of indistinct or barely visible somatic setae present in pharyngeal region, absent on remainder of body. Cephalic capsule either smooth or partly to entirely ornamented with small vacuoles (in inner cuticle). Four cephalic setae located in vicinity of fovea amphidialis; subcephalic setae absent. Fovea amphidialis cryptospiral, spiral or multispiral (may vary from 1.25 to 3 turns). Reproductive system monorchic, with single anterior testis situated to left of intestine, outstretched; short spicules, capitulum present, velum may be present. Precloacal setae may be present. Female reproductive system didelphic, amphidelphic with reflexed ovaries.

Type species Spinonema cuticulatum gen. et sp. n.

Etymology. The name refers to the spine present on the dorsal side (Latin spina) combined with nema, thread (Greek νῆμα); gender neuter.

Relationships. Spinonema gen. n. is assigned to the subfamily Desmodorinae based on the well-developed head capsule with thick cuticle, buccal cavity with teeth, and cuticle with transverse annuli except in the head region. Spinonema gen. n. has some features in common with Desmodora de Man, 1889 , e.g., well-developed cephalic capsule (in some species with vacuoles), shape of fovea amphidialis (cryptospiral and spiral) and small arched spicules. Spinonema gen. n. and Desmodora differ in the body annuli (annulated cuticle in Spinonema gen. n.), absence of subcephalic setae, and cuticular ornamentation (lateral alae; may have pharyngeal dorsal spine in Spinonema gen. n.). Spinonema gen. n. resembles Desmodorella Cobb, 1933 in the shape of the fovea amphidialis (cryptospiral and multispiral) and cuticular ornamentation, but differs mainly in the type of ornamentation: Desmodorella has a differentiation in the cuticle composed of longitudinal spines; whereas Spinonema gen. n. has C-shaped lateral alae, oriented anteriorly, with no spines; smaller and arched spicules; and a velum may be present.

Other comparable genera are Pseudochromadora Daday, 1899 and Psammonema Verschelde & Vincx, 1995 . Both have lateral alae but differ in the size of the alae: in these two genera the alae occupy nearly the whole body, in Spinonema gen. n. the alae occupy only a small portion of the body. The alae of Spinonema gen. n. differ in being smaller and in the most central region of the body. Usually the lateral alae are observed longitudinally (e.g., Pseuchromadora and Psammonema ), in the cervical or caudal region (observed in males, e.g., Zalonema Cobb, 1920 ). In Spinonema gen. n., lateral alae are formed by raised and bent lateral sections of annules, resembling the letter C. C-shaped refers to each individual segment of ala and annuli. The lateral alae are curved anteriorly. See Figure 2 . This form and type of alae are unique in the subfamily Desmodorinae .

Remarks. The main characteristic of the subfamily Desmodorinae is the well-developed cephalic capsule without annulations. Accordingly, some genera were transferred to Spiriniinae because their members lack a welldefined cephalic capsule (e.g., Stygodesmodora Blome, 1982 ; Echinodesmodora Blome, 1982 ; Paradesmodora Schuurmans Stekhoven, 1950 and Parallelocoilas Boucher, 1975 ) ( Armenteros et al., 2014), supporting the assignment of this new genus to the subfamily Desmodorinae .

List of valid genera of Desmodorinae (14) (after Armenteros et al. 2014): Acanthopharyngoides Chitwood, 1936 ; Acanthopharynx Marion, 1870 ; Bolbonema Cobb, 1920 ; Cornurella da Silva, Silva, Esteves & Decraemer, 2018 ; Croconema Cobb, 1920 ; Desmodora de Man, 1889 ; Desmodorella Cobb, 1933 ; Onepunema Leduc & Verschelde, 2013 ; Psammonema Verschelde & Vincx, 1995 ; Pseudochromadora Daday, 1899 ; Pseudodesmodora Boucher, 1975 ; Sibayinema Swart & Heyns, 1991; Spinonema gen. n.; Zalonema Cobb, 1920 .

Figures

FIGURE 2. Lateral alae of the species S. cuticulatum gen. et. sp. n. (A and D); S. spirale gen. et sp. n. (B and E) and S. absente gen. et sp. n. (C and F). Anterior part (ANT) and Posterior part (POS).