Spinonema cuticulatum, 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 : 325-329

Spinonema cuticulatum gen. et sp. n.

( Table 1 , Figures 3–5 )

Type material: Holotype, Male adult MNRJ 396 (05°00’12.7’’S 036°23’27.7’’W) collected in June 2009 from the Potiguar Basin, between 30 and 45 m deep. Faciology: fine to coarse bioclastic sand. Gear: Van Veen grab.

Paratype female: Adult, MNRJ 397 (05°01’36.1’’S 036°24’32.4’’W) collected in June 2009 from the Potiguar Basin, between 30 and 45 m deep. Faciology: fine to coarse bioclastic sand. Gear: Van Veen grab .

Other paratypes: 2 females (198-199 LMZOO-UFPE), 5 males (200-204 LMZOO-UFPE) and 5 juveniles. Two in second stage of development (J2) and three in first stage of development (J1) (205 LMZOO-UFPE) collected on same date as holotype. Juvenile stages were identified based on the developmental stage of the reproduc- tive system, based on Bird and Bird (1991).

Etymology. The species name refers to the ornate cuticle.

Description. Male Holotype ( Figures 3 and 4 ). Body cylindrical, yellowish brown. Cephalic capsule present. Cuticle coarsely annulated, with irregularly distributed vacuoles that start to appear from 9 th (9-15 th for paratypes) cuticular annule. The vacuoles are in the inner layer of the cuticle and not in its exterior. Annuli ornamented similarly to those in members of family Epsilonematidae . Annulations absent on tail end with vacuoles. Cuticle with lateral alae C-shaped, thicker than rest of body ( Figures 3 and 4 ). Lateral alae begin 422 µm (378-467 µm for paratypes) from head.Annules 3 µm wide in anterior region, 2 µm at midline and 3 µm in posterior region. Somatic setae indistinct or barely visible in pharyngeal region. Few somatic setae and papillae irregularly distributed along body. Dorsal spine strongly cuticularized, located on 18 th (for all specimens) cuticular annule (pharynx region), consisting of cuticular projection ( Figures 3C and 4A ). Inversion of direction of annuli occus after 81 rd (77-83 rd for paratypes) cuticular annule. Head triangular. 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 positioned at midlevel of fovea amphidialis. Fovea amphidialis spiral (1.25 turns for all specimens), occupying 65% (46-70% for paratypes) of head diameter. Oral cavity with one small dorsal tooth and one small ventral tooth. Pharynx cylindrical, with muscular pyriform endbulb. 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. Only one midventral precloacal setae present. Spicules short, arched, and capitulum hook-shaped ( Figure 3F ). Broad velum present. Gubernaculum simple, without apophysis. Three ejaculatory glands and three caudal glands. Tail short, conical, with vacuoles. Spinneret short.

Paratype females ( Figures 4 and 5 ). Similar to male in body size, with minor differences: vacuoles present in cuticle appear on 15-18 th annule. Inversion of direction of annuli occurring after 74-79 th cuticular annule. Lateral alae begin 377-423 µm from head. Reproductive system with paired ovaries, opposite and reflexed antidromously; both genital branches to right of intestine. Vulva as simple transverse slit-like aperture. Vagina vera slightly cuticularized. Vagina uterina surrounded by constrictor muscle. No egg found in uterus ( Figure 5D ). Vulva located at 39-40% of total body length from anterior end. Tail conical.

Juveniles ( Figure 5 ). Very similar to adults, except lacking lateral alae. Fovea amphidialis is very similar to the adults. Five juveniles were found, three in stage 1 and two in stage 2.

Diagnosis. Spinonema cuticulatum gen. et sp. n. is characterized by the annulated cuticle with vacuoles along the body, a spiral fovea amphidialis (1.25 turns), one dorsal spine in pharyngeal region, lateral alae, spicules arched with the capitulum hook-shaped, velum present, and three ejaculatory glands.

Relationships. Spinonema cuticulatum gen. et sp. n. is similar to Desmodora in the presence of a spiral fovea amphidialis (e.g. Desmodora communis ( Bütschli 1874) ; Desmodora coniseta (Schuurmans Stekhoven, 1950) ; Desmodora ignava Gagarin & Klerman 2008 ), arched spicules with a velum ( Desmodora granulata Vincx & Gour- bault 1989; Desmodora marci Verschelde, Gourbault & Vincx 1998 ; Desmodora masira Warwick 1973 ) and the buccal cavity with one dorsal and one ventral tooth (seldom present in Desmodora ). It differs from Desmodora in the morphology of the cuticle: S. cuticulatum gen. et sp. n. has an annulated cuticle with lateral alae and a pharyngeal dorsal spine. The new species is comparable to Croconema Cobb, 1920 in having the cephalic capsule offset and strongly annulated, and in some species in the presence of a velum (e.g. Croconema otti Gourbault & Vincx 1990 ). It can be distinguished from Croconema by the absence of somatic and subcephalic setae. Another similar genus is Desmodorella in the spiral shape of the fovea amphidialis (e.g. Desmodorella filispiculum ( Lorenzen 1976) ; Desmodorella papillostoma ( Murphy 1962) ; Desmodorella perforata ( Wieser 1954) and the ornamentation on the cuticle, but differs mainly in the type of ornamentation. In Desmodorella the ornamentation consists of longitudinal rows of spines on the cuticle; whereas in S. cuticulatum gen. et sp. n. the ornamentation consists of lateral alae in the form of a ridge. Thus, this species can be distinguished from any other species/genus by the combination of three characteristics: annulated cuticle with vacuoles, pharyngeal dorsal spine, and lateral alae.

Figures

FIGURE 3. Spinonema cuticulatum gen. et sp. n. Holotype MNRJ 396. A and C: anterior region; B: overview; E: lateral alae (ANT anterior part and POS posterior part); D and F: copulatory apparatus; G: tail region; H: Inversion of direction of annuli.

FIGURE 4. Spinonema cuticulatum gen. et sp. n. A, B and E Holotype MNRJ 396; A: Cephalic region; B: Spicules; E: Lateral alae (ANT anterior part and POS posterior part). C and D Paratype female MNRJ 397; C: Cephalic region; D: Tail region.

FIGURE 5. Spinonema cuticulatum gen. et sp. n. Paratype female MNRJ 397. A: overview; B and C: anterior region; D: ovary and vulva opening; G: tail region. E and F: juvenile in stage 1, anterior region.