Stygodesmodora robusta, Larrazábal-Filho & Neres & Esteves, 2017

Larrazábal-Filho, Alexandre L., Neres, Patrícia F. & Esteves, André M., 2017, Four new species and an identification key for Stygodesmodora Blome, 1982 (Nematoda: Spiriniinae) from the continental shelf off northeastern Brazil, Zootaxa 4294 (1) : -

Stygodesmodora robusta sp. n.

(measurements in Table 4, Figs 8–10 ).

Type material. Holotype male, adult MNRJ 386. Station ME1D1 (05°01’47”S, 036°23’44”W). Paratype female, adult, MNRJ 387. Station ME1C2 (05°01’11”S, 036°23’45”W). Other paratypes, six females (210 and 214 LMZOO-UFPE), 11 males (215–219 LMZOO-UFPE), and five J1 and five J3 (220 LMZOO-UFPE), same data as for holotype.

Etymology. The species epithet is given for the strong body shape.

Description. Holotype ( Figs 8–9 ). Body robust, long and cylindrical, yellowish brown. Cuticle strongly annulated except in final portion of tail, no lateral differentiation. Ventral ala absent. Somatic setae arranged in eight longitudinal rows: two dorsal, four lateral and two ventral. Head region with annulations completely surrounding amphid ( Fig. 8 B). In some specimens, labial region folded inward. Anterior sensilla arrangement: six outer labial papillae (difficult to see), four cephalic setae, and eight cervical setae. Cervical setae arranged in two circles: four at anterior edge of fovea amphidialis and four at posterior edge of fovea ( Fig. 8 B). Fovea amphidialis cryptospiral, occupying 57% of diameter of head, located on cuticularized amphideal plate. Oral cavity with one dorsal tooth and one ventral tooth. Pharynx cylindrical, with muscular and slightly elongated endbulb. Nerve ring, ventral gland and excretory-secretory pore obscured by thick cuticle, not observed. Cardia inserted in intestine (difficult to see). Reproductive system monorchic, with single anterior testis situated to left of intestine, outstretched. Spermatic cells globular. Spicules large and arched, proximal region rounded, well developed and with hook-shaped invagination. Laminar of gubernaculum positioned dorsally, without apophysis. Velum absent. One row of nine ventrally placed precloacal setae ( Fig. 8 C). Tail conical, with three small terminal setae, three caudal glands, and spinneret.

Paratype female ( Figs 9–10 ). Similar to male, with minor differences: four cervical setae positioned at midlevel of fovea amphidialis . Reproductive system with paired ovaries, opposite and reflexed, situated to left of intestine. Vulva as transverse slit. Vagina vera short, vagina uterina with sphincter muscle. No eggs. Globular spermatic cells visible in uterus. Vulva comprising 60% of total body length (886.5 µm from anterior end). Tail conical.

Juveniles. Very similar to adults, except lacking some characteristics such as supplements. Reproductive system immature. Juveniles in stage 1 lack cervical setae and have very few somatic setae along the body. Juveniles in stage 3 have four cervical setae and somatic setae along the body. Ten juveniles found, five in stage 1 and five in stage 3.

Diagnosis. Stygodesmodora robusta sp. n. is characterized by the long, robust body, strongly annulated cuticle, nine to 13 precloacal setae, and spicules large and arched, proximal region rounded, well developed and with hookshaped invagination.

Differential diagnosis. Stygodesmodora robusta sp. n. can be compared with S. confusa in the presence of somatic setae along the body and the presence of setiform supplements. It differs in the cephalic setae arrangement (cervical setae absent in S. confusa ), buccal cavity (ventral tooth absent in S. confusa ) and number of supplements ( S. robusta sp. n. with 9–13 setae vs. S. confusa with 4 setae).

Stygodesmodora robusta sp. n. is similar to S. bacillicauda in the annulated cuticle and buccal cavity. However, S. bacillicauda has more somatic setae than in S. robusta sp. n. Furthermore, S. bacillicauda lacks cervical setae and supplements (both features are present in S. robusta sp. n.).

Stygodesmodora robusta sp. n. is similar to S. epixantha in the strongly annulated cuticle, cephalic arrangement (four cephalic and eight cervical setae), buccal cavity (one dorsal and one ventral tooth). It differs in the shape and number of supplements (papilliform in S. epixantha vs. setiform in S. robusta sp. n.), absence of velum (present in S. epixantha ), non-annulated tail end (shorter in S. epixantha than in S. robusta sp. n.), shape of capitulum (rounded in S. epixantha and hook-shaped in S. robusta sp. n.), and shape of gubernaculum (terminal region wing-shaped in S. epixantha and laminar in S. robusta sp. n.).

Stygodesmodora robusta sp. n. can be distinguished from S. amphidialis sp. n. and S. paramphidialis sp. n. by the strongly annulated cuticle (larger and thicker in S. robusta sp. n. than in S. amphidialis sp. n. and S. paramphidialis sp. n.), shape of supplements (precloacal setae in S. robusta sp. n.), size of fovea amphidialis (larger in S. amphidialis sp. n. and S. paramphidialis sp. n. than in S. robusta sp. n.) and absence of a velum (in S. robusta sp. n.).

Sex Male Female Juvenile

Figures

FIGURE 8. Stygodesmodora robusta sp. n. Holotype male MNRJ 386. A: Overview; B: Head region; C: Tail region; D: Copulatory apparatus; E: Anterior region.

FIGURE 9. Stygodesmodora robusta sp. n. A – C: Paratype female MNRJ 387; A – C: Cephalic region; C: Tail region. D – F: Holotype male MNRJ 386; D: Tail region; E – F: Cephalic region and fovea amphidialis.

FIGURE 10. Stygodesmodora robusta sp. n. A: Head region of paratype female MNRJ 387; B: Head region of juvenile (J 3); C: Anterior region of juvenile (J 3); D: Anterior region of paratype female MNRJ 387; E: Tail region of paratype female MNRJ 387; F: Overview of paratype female MNRJ 387; G: Ovary and vulva opening of paratype female MNRJ 387.