Spinonema absente, 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 : 334-339

Spinonema absente gen. et sp. n.

( Table 3, Figures 9–11 ).

Type material: Holotype, Male adult MNRJ 400 (04°45’00”S, 036°45’00”W) collected in June 2009 in the Po- tiguar Basin, between 30 and 35 m deep. Faciology: coarse bioclastic sand. Gear: Van Veen /corer.

Paratype female: Adult, MNRJ 401 (05°01’20.4’’S 036°11’14.0’’W) from the Potiguar Basin, between 30 and 35 m deep. Faciology: coarse lithoclastic sand. Gear: Van Veen /corer .

Other paratypes: 4 females (210-213 LMZOO-UFPE), 5 males (214-218 LMZOO-UFPE) and 5 juveniles. Four in first stage of development (J1) and one in fourth stage of development (J4) (219 LMZOO-UFPE), collected on same date as holotype. Juvenile stages were identified based on the developmental stage of the reproductive system, based on Bird and Bird (1991).

Etymology. This species lacks a dorsal spine. L. absentia, absence.

Description. Holotype ( Figures 9–10 ). Body cylindrical, yellowish brown. Cuticle annulated, with irregularly distributed vacuoles that start to appear from 6 th (5-12 th for paratypes) cuticular annule. The vacuoles are in the inner layer of the cuticle and not in its exterior. Annulations absent on tail end with vacuoles. Cuticle with lateral alae, thicker than rest of body, reaching only 19 (17-25) rings of total body length. Lateral alae begin 468 µm (378-473 µm for paratypes) from head. Annules in anterior region are 4.5 µm wide, at midline 4 µm, and in posterior region 3.5 µm. Sparse somatic setae irregularly distributed along body. Somatic setae indistinct or barely visible in pharyngeal region. Inversion of direction of cuticular annuli occurring after 80 th (80 th- 89 th for paratypes) cuticular ring. Cephalic capsule long and well developed, with thick cuticle without annulations. Anterior sensilla arrangement: six inner and six outer labial sensilla, both papilliform. Four cephalic setiform sensilla located at level with upper portion of fovea amphidialis. Fovea amphidialis cryptospiral, occupying 58% (50-62%) of diameter of head. Oral cavity with one dorsal tooth and one (or two, difficult to see) ventral tooth. Cylindrical pharynx with muscular and pyriform basal bulb. Ventral gland and secretory-excretory pore not observed. Cardia inserted in intestine. Reproductive system monorchic, with single anterior testis situated to left of intestine, outstretched. Globular sperm cells. Spicules arched, cuticularized and capitulum rounded. Velum absent; gubernaculum laminar, without apophysis ( Figure 9C ). Three caudal glands. Tail conical with numerous vacuoles. Three precloacal setae ( Figure 10F ). Spinneret conical.

Females ( Figures 10–11 ). Similar to male in body size and with minor differences: inversion occurs after 79 th (75 th- 89 th) cuticular ring. Lateral alae begin 442 µm (387-459 µm) from head. Reproductive system with paired ovaries, opposite and reflexed antidromous; both genital branches to right of intestine. Vulva as simple transverse slit-like aperture. Vagina vera and vagina uterina weakly cuticularized. No egg found. Vulva located at 57% (40- 56%) of total body length from anterior end. Tail conical.

Juveniles ( Figure 11 ). Similar to adults, except lacking some characteristics including supplements and lateral alae; reproductive system immature. Fovea amphidialis is very similar to the adults. Juveniles in stage 1 lack so- matic setae arranged in rows. Five juveniles were found, four in stage 1 and one in stage 4.

Diagnosis. Spinonema absente gen. et sp. n. is characterized by having a cuticle with irregularly distributed vacuoles that start to appear from the 6 th cuticular ring, a cryptospiral fovea amphidialis, absence of pharyngeal dorsal spine, presence of lateral alae, and three precloacal setae in male.

Relationships. Spinonema absente gen. et sp. n., S. spirale gen. et sp. n. and S, cuticulatum gen. et sp. n. are similar in the presence of vacuoles, the inversion ring and the lateral alae, although varying in length (these three features are on the cuticle). Spinonema absente gen. et sp. n. differs from the others in the absence of the dorsal spine, shape of the fovea amphidialis ( S. cuticulatum gen. et sp. n. spiral and S. spirale gen. et sp. n. multispiral), rounded capitulum ( S. cuticulatum gen. et sp. n. hook-shaped), gubernaculum without apophysis ( S. spirale gen. et sp. n. gubernaculum intricate with lateral crurae and dorsal apophysis) and presence of three precloacal setae (absent in S. spirale gen. et sp. n. and one in S. cuticulatum gen. et sp. n.).

Figures

FIGURE 9. Spinonema absente gen. et sp. n. Holotype MNRJ 400. A: overview; B, C and F: anterior region; D: tail region; E: spicules; H: lateral alae (ANT anterior part and POS posterior part); G: Inversion of direction of annuli.

FIGURE 10. Spinonema absente gen. et sp. n. A and C, Holotype male MNRJ 400; A: Cephalic region; C: Tail region. B, D, E and F, Paratype female MNRJ 401; B: Tail region; D: Lateral alae (ANT anterior part and POS posterior part); E: Vulva opening; F: Anterior region.

FIGURE 11. Spinonema absente gen. et sp. n. Paratype female MNRJ 401. A: overview; C: Ovary and vulva opening; B and D: Anterior region. Paratype juvenile in stage 4. E: Anterior region; F: Tail region; G: Ovary of juvenile.