Stygodesmodora potiguensis, 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 potiguensis sp. n.

(measurements in Table 5, Figs 11–13 ).

Type material. Holotype male, adult MNRJ 388. Station ME1D1 (05°01’47”S, 036°23’44”W). Paratype female, adult, MNRJ 389. Station ME2C2 (05°02’18”S, 036°23’23”W). Other paratype, one J2 (221 LMZOO-UFPE), same data as for holotype.

Etymology. The specific epithet “ potiguensis ” is given for the location where the material was found, in the Potiguar Basin.

Description. Holotype ( Figs 11–12 ). Body relatively long, cylindrical, yellowish brown, tapering slightly toward each end. Cuticle annulated except in final portion of tail, no lateral differentiation. Ventral ala absent. Many somatic setae, irregularly distributed along body. Head region with annulations completely surrounding fovea amphidialis . Anterior sensilla arrangement: six outer labial papillae (difficult to see), four cephalic setae, and four cervical setae. Cervical setae positioned at mid-level of fovea amphidialis ( Fig. 11 A). Fovea amphidialis large, cryptospiral, occupying 90% of diameter of head, located on cuticularized amphideal plate. Oral cavity with one dorsal tooth and one ventral tooth. Pharynx cylindrical with muscular and pyriform endbulb. Nerve ring, ventral gland and excretory-secretory pore not observed. Cuticle and somatic setae strongly cuticularized and obscuring internal structures. Cardia inserted in intestine. Reproductive system monorchic, with single anterior testis situated to left of intestine, outstretched. Spicules arched, proximal region rounded and hook-shaped ( Fig. 11 E). Velum absent; gubernaculum simple, well developed. Caudal and precloacal regions with few setae. Supplements absent. Tail conical-cylindrical, with three small caudal glands and spinneret.

Paratype female ( Figs 12–13 ). Similar to male in body size, with minor differences: fovea amphidialis smaller than in male and cephalic arrangement different (i.e. two sexual dimorphisms). Cervical setae arranged in two circles: four at mid-level of fovea amphidialis and four just below fovea. Reproductive system with paired ovaries, opposite and reflexed, situated to right of intestine. Vulva as transverse slit. Vagina vera short, vagina uterina with sphincter muscle. No egg found. Vulva comprising 37% of total body length (456 µm distant from anterior end). Tail conical.

Juveniles. Very similar to adults, except lacking some characteristics such as supplements, with an immature reproductive system, and the size of the fovea amphidialis (smaller than males). Juveniles in stage 2 have four cervical setae and some somatic setae along the body. One juvenile was found, in stage 2.

Diagnosis. Stygodesmodora potiguensis sp. n. is characterized by having the cuticle strongly annulated, many somatic setae along the body, sexual dimorphism in the size of the fovea amphidialis , and supplements absent.

Differential diagnosis. Stygodesmodora potiguensis sp. n. is similar to S. bacillicauda in the annulated cuticle, many somatic setae along the body, and the absence of supplements. However, S. bacillicauda lacks cervical setae, the shape of the capitulum is different (rounded in S. bacillicauda vs. rounded and hook-shaped in S. potiguensis sp. n.), the gubernaculum (in S. bacillicauda the distal portion of the gubernaculum is enlarged) and the tail (conical in S. bacillicauda vs. conical-cylindrical in S. potiguensis sp. n.).

Stygodesmodora potiguensis sp. n. is similar to S. epixantha in the cephalic arrangement (four cephalic setae) and buccal cavity (one dorsal and one ventral tooth). It differs in the size of the fovea amphidialis (larger in S. potiguensis , at 90%, than in S. epixantha at 55%), the number of somatic setae along the body ( S. potiguensis sp. n. has many more setae), the lack of a velum (present in S. epixantha ) and the shape of the capitulum (rounded in S. epixantha ).

Sex Male Female Juvenile Holotype Paratype Paratype

Number of specimens 1 1 1

Body length 1184 1240 812 Pharynx length 172.5 180 132 Maximum body diameter 38 42 36 Anal body diameter 30 28.5 24 Tail length 99 99 81 Tail end length 24 24 22.5 Head diameter 23.5 20 17 Length of cephalic setae 9 9.5 8.5 Percentage of bulb diameter 68 66 72 Fovea amphidialis diameter (%cephalic capsule) 90 42 44 Amphideal width 21.5 8.5 7

Amphideal height 24.5 8.5 6

Length of spicules 46 ‾ ‾

Gubernaculum length 14 ‾ ‾

Anterior to vulva ‾ 456 ‾

Position of vulva as percentage of body length from anterior end ‾ 37 ‾

a 3 1 2 9 2 2.5 b 7 7 6

c 12 12.5 10 Stygodesmodora potiguensis sp. n. resembles Stygodesmodora confusa in the presence of somatic setae. It differs in the cephalic arrangement (cervical setae absent in S. confusa ), shape of the capitulum (rounded in S. confusa ), the presence of a velum (absent in S. potiguensis sp. n.), and the size of the fovea amphidialis (larger in S. potiguensis sp. n.).

Stygodesmodora potiguensis sp. n. can be distinguished from the other new species described here by the presence of many somatic setae along the body and the absence of supplements.

Figures

FIGURE 11. Stygodesmodora potiguensis sp. n. Holotype MNRJ 388. A: Head region; B: Overview; C: Anterior region; D: Tail region; E: Copulatory apparatus.

FIGURE 12. Stygodesmodora potiguensis sp. n.: A – B, F: Paratype female MNRJ 389; C – E: Holotype male MNRJ 388. A: Cephalic region; B: Vulva opening; C: cephalic region and fovea amphidialis; D: Spicules; E: Male tail region; F: Female tail region.

FIGURE 13. Stygodesmodora potiguensis sp. n. A: Head region of paratype female MNRJ 389; B: Head region of juvenile (J 2); C: Anterior region of juvenile (J 2); D: Anterior region of paratype female MNRJ 389; E: Overview of paratype female MNRJ 389; F: Ovary and vulva opening of paratype female MNRJ 389; G: Tail region of paratype female MNRJ 389.