Two new species of Microlaimidae (Nematoda: Microlaimida) from the Continental Shelf off Northeastern Brazil (Atlantic Ocean) with emended diagnosis and dichotomous key

Systematics

Diagnosis. (Emended from Shi & Xu, 2016) Microlaimidae. Cuticle annulated. Anterior sensilla in three circles: six inner labial setae papilliform; six stout outer labial setae (sometimes jointed); and four cephalic setae shorter or similar in length to the six outer labial setae. Buccal cavity large, armed with a well-developed dorsal tooth and a pair of ventrosublateral teeth. Additional lateral teeth may be present. Amphidial fovea multispiral and ventrally wound, sclerotized. Postamphidial setae in six or eight longitudinal rows. Pharynx with anterior bulb. Oval posterior bulb present or absent. Females with two outstretched ovaries. Males with two opposed testes. Copulatory apparatus strongly sclerotized. Gubernaculum with or without apophysis. Precloacal supplements (papilliform or small pores) present or absent. Oval, elongated or banana-shaped sperm cells. Tail conical.

Type species: Spirobolbolaimus bathyalis Soetaert & Vincx, 1988.

List of valid species of SpirobolbolaimusSoetaert & Vincx, 1988

Description of new species

Spirobolbolaimus pernambucanus sp. nov.

(Table 1; Figs. 1–4)

Material studied. Holotype male (MOUFPE 0022), paratype female (MOUFPE 0023), 1 male paratype (485 NM LMZOO-UFPE) and 2 female paratypes (486–487 NM LMZOO-UFPE).

Type locality. South Atlantic Ocean, Continental shelf off the State of Pernambuco, Brazil, (S08°16′17.10″  W34°39′34.80″), November 26, 2019, 52 m.

Locality of paratypes. Female paratypes: South Atlantic Ocean, Continental shelf off the State of Paraíba, Brazil (S07°25′15.48″  W34°29′16.56″), November 27, 2019, 47 m. Paratype male 1: South Atlantic Ocean, Continental shelf of the State of Pernambuco, Brazil (S08°16′17.10″  W34°39′34.80″), November 26, 2019, 52 m.

Etymology. Due to the location where the holotype was collected. Pernambucanus is the Latinized form of the term “pernambucano”. In Brazil, “pernambucano” refers to something or someone originating from the state of Pernambuco.

Holotype male. Body cylindrical (1,716 µm long), slightly narrow anteriorly. Maximum body diameter corresponding to 1.2 times the head diameter. Head blunt, slightly set-off. Cuticle striated from the posterior edge of the amphidial fovea. Cuticular pores not observed. Anterior sensilla arranged in the 6 + 6 + 4 pattern: six inner labial papillae (2 µm long), six outer labial setae with a broad base (7 µm long) and four slender cephalic setae about the same length as the outer labial setae. Cephalic setae corresponding to 21% of head diameter. Amphidial fovea distinctly sclerotized, multispiral, ventrally wound, about 3.5 turns, occupying 36% of corresponding body diameter and located 0.4 times the head diameter of the anterior end. Buccal cavity with a strong dorsal tooth and two ventrosublateral teeth located at the same level. Cheilostoma possesses 12 rugae. Eight rows of cervical setae starting 11 µm behind the amphid fovea. Pharynx (220 µm) with anterior bulb surrounding the buccal cavity. Basal bulb is oval and not very prominent, occupying 67% of corresponding body diameter. Cardia embedded in intestine. Nerve ring situated at 55% of the pharynx length, from anterior end. Ventral gland and secretory-excretory pore not observed. Reproductive system with two opposed and outstretched testes, both to the left of the intestine. Elongated sperm cells. Spicules sclerotized with a capitulum. Gubernaculum plate-like with dorsal apophysis. Twelve pore-like precloacal supplements present and arranged at irregular intervals. The closest supplement to the cloaca is located at 24.5 µm and the farthest at 258.5 µm. A pair of precloacal ventrosublateral setae located between the cloaca and the closest supplement to it. Three caudal glands. Tail conical (four times the cloacal body diameter) with two rows of short ventrosublateral setae.

Paratype female. Similar to male. Body length 1,752 µm, maximum diameter 46.5 µm (1.3 times the head diameter). Cuticle striated behind the posterior edge of the amphidial fovea. Anterior sensilla arrangement consisting of six inner labial papillae (2 µm long), six outer labial setae with a broad base (7 µm long) and four slender cephalic setae (6 µm long, corresponding to 17% of head diameter). Amphidial fovea sclerotized, multispiral, ventrally wound, about three turns, occupying 35% of corresponding body diameter and located 0.3 times the head diameter of the anterior end. Buccal cavity with a strong dorsal tooth and two ventrosublateral teeth. Pharynx similar to that of males. Basal bulb is oval and not very prominent (66% of corresponding body diameter). Nerve ring located at 56% of the pharynx length. Vulva situated at 55% of body length. Reproductive system didelphic-amphidelphic, with outstretched ovaries. Anterior gonad situated to right side of intestine and the posterior gonad to left side of intestine. Tail conical (131 µm long), about four times anal body diameter.

Diagnosis. Spirobolbolaimus pernambucanus sp. nov. it is characterized by its body length (1,716–1,848 µm). Cuticle striated. Head blunt, slightly set-off. Six outer labial setae with a broad base and four slender cephalic setae about the same length as the outer labial setae. Amphidial fovea sclerotized, multispiral, ventrally wound, about 3–3.5 turns, occupying 31–36% of the corresponding body diameter, located at about 0.2–0.4 times the head diameter. Eight rows of cervical setae. Buccal cavity with a strong dorsal tooth and two ventrosublateral teeth. Spicules sclerotized with a capitulum (1.5–1.7 times the cloacal body diameter) and gubernaculum plate-like with dorsal apophysis. Twelve pore-like precloacal supplements. Tail conical which corresponds to 3–4 cloacal or anal body diameter.

Differential diagnosis. Spirobolbolaimus pernambucanus sp. nov. shares the following features with S. undulatus: number of longitudinal rows of cervical setae (eight in both species), spicules length (53–55 µm in the new species and 51–55 µm in S. undulatus) and the ratio between spicules length and the cloacal body diameter (1.5–1.7 in S. pernambucanus sp. nov. and 1.3–1.5 in S. undulatus). Nevertheless, S. pernambucanus sp. nov. differs from S. undulatus in terms of body length (1,686–1,848 µm in the new species vs 2,035–2,558 µm in S. undulatus), the absence of jointed outer labial setae (vs outer labial setae jointed in S. undulatus), the presence of outer labial setae about the same length as the cephalic setae (vs outer labial setae longer than cephalic setae in S. undulatus) and the number of precloacal supplements (12 pore-like precloacal supplements in the new species vs 18–19 precloacal supplements in a series of mid-ventral elevations with pores on tops in S. undulatus). Furthermore, additional teeth are absent in S. pernambucanus sp. nov. (vs present in S. undulatus).

Spirobolbolaimus pernambucanus sp. nov. shares some features with adult specimens of S. boucherorum, such as: body length (1,686–1,848 µm in the new species vs 1,460–1,870 µm in S. boucherorum), amphidial fovea diameter (11–12 µm in S. pernambucanus sp. nov. and 10–12 µm in S. boucherorum) and de Man’s ratio c (13–16 in the new species and 12–17 in S. boucherorum). However, S. pernambucanus sp. nov. differs from S. boucherorum in terms of the number of precloacal supplements (12 in the new species vs seven in S. boucherorum), the length and shape of the gubernaculum (19–19.5 µm in S. pernambucanus vs 23–30 µm in S. boucherorum) and the presence of outer labial setae that are about the same length as the cephalic setae (vs outer labial setae longer than cephalic setae in S. boucherorum). A comparison of the main characters of all valid species of Spirobolbolaimus is presented in Table 2.

Dichotomous identification key for valid species of SpirobolbolaimusSoetaert & Vincx, 1988

Genus IxonemaLorenzen, 1971

Diagnosis. (Emended from Tchesunov, 2014) Microlaimidae. Cuticle finely striated but can appear smooth and may be covered with sediment particles. Anterior sensilla arranged according to 6 + 6 + 4 pattern: six inner labial papillae; six outer labial papillae; and four cephalic setiform sensilla. Anterior end narrowed and elongated. Amphid fovea small circular or pocket-shaped, far posterior to the anterior end, with protruding rod-shaped corpus gelatum (not seen in some species, lost/broken or absent?). Buccal cavity small, armed with a dorsal tooth and a pair of ventrosublateral teeth (additional small teeth posterior to ventrosublateral may be present). Somatic setae stout or on peduncles, sometimes jointed, arranged in rows along the body. Males with two opposite and outstretched testicles. Precloacal supplements in the form of jointed or non-jointed setae may be present. Ventral supplements in the form of jointed setae located just behind the pharynx may be present. Gubernaculum present or absent, when present without apophyses. Female didelphic-amphidelphic, with outstretched ovaries. Tail conical. Each caudal gland with its own outlet on the tail tip.

Type species: Ixonema sordidum Lorenzen, 1971

List of valid species of IxonemaLorenzen, 1971

Description of new species

Ixonema gracieleae sp. nov.

(Table 3; Figs. 5–9)

Material studied. Holotype male (MOUFPE 0024), paratype female (MOUFPE 0025), 3 male paratypes (488–490 NM LMZOO-UFPE) and 2 female paratypes (491–492 NM LMZOO-UFPE).

Type locality. South Atlantic Ocean, Continental shelf off the State of Alagoas (S09°39′14.52″ W35°15′21.66″), November 25, 2019, 50 m. The paratypes were found in the same locality.

Etymology. The specific epithet is a tribute to Graciele Mariza dos Santos Alves, wife of the first author.

Holotype male. Body cylindrical, short and plump, attenuating on both ends and thick in the middle (586.5 µm long). Maximum body diameter corresponding to 4.1 times the head diameter. Cuticle finely striated, the striations are so delicate that they are difficult to visualize (striations are most visible on the tail). Anterior sensilla arranged in the 6 + 6 + 4 pattern: six inner labial papillae, six outer labial papillae and four cephalic setae (6 µm long). Cephalic setae corresponding to 74% of head diameter. Amphidial fovea small and circular, occupying 25% of corresponding body diameter and located far posterior to the anterior end (four times the head diameter of the anterior end). Protruding Corpus gelatum not observed. Buccal cavity with a dorsal tooth and two small ventrosublateral teeth. Cheilostoma rugae indiscernible under a light microscope. Four sublateral rows of stout cervical setae located between the posterior region of the cephalic setae and the base of the amphidial fovea. The first row is 24 µm from the anterior end and the second is at the same height of the amphidial fovea base, 31 µm from the anterior end. Six rows of cervical setae on peduncles located between the posterior region of the amphidial fovea and close to the bulb base: four sublateral rows where relatively smaller setae (4–7 µm) and long setae (10–16 µm) alternate; two lateral rows (about 4 µm). The first row is about 11 µm from the base of the amphidial fovea. After the cervical region, the somatic setae are distributed in two rows where the alternation between two smaller setae (about 5–9 µm) and a larger one (12–19 µm) usually occurs. Pharynx (104 µm) with prominent terminal bulb, occupying 73% of corresponding body diameter. Cardia embedded in intestine. Nerve ring situated at 60% of the pharynx length, from anterior end. Ventral gland and secretory-excretory pore not observed. Reproductive system with two opposed and outstretched testes on right side of intestine. Spicules curved (39 µm), about two times the cloacal body diameter. Gubernaculum slender and without apophysis. Four setiform ventral supplements: three precloacal supplements plus one located just behind the pharynx. The two setae closest to the cloaca (10.5 µm and 40 µm anterior to the cloaca, respectively) are jointed, measuring 7 µm and 6 µm respectively; the third precloacal seta is smaller (about 2 µm length), apparently non-jointed in light microscopy and far from the cloaca (62 µm). The setae located just behind the pharynx (about 7 µm length) are jointed (morphologically similar to the two setae closest to the cloaca) and are located 84 µm from the anterior end. Tail conical (73 µm long), with a blunt tip where the three caudal glands open through separate outlets into papilla-like extensions.

Paratype female. Similar to male. Body measuring 667.5 µm in length, maximum diameter 36 µm (4.3 times the head diameter). Cuticle finely striated, the striations are so delicate that they are difficult to visualize. Anterior sensilla arranged in the 6 + 6 + 4 pattern: six inner labial papillae, six outer labial papillae and four cephalic setae (7 µm long, corresponding to 88% of head diameter). Amphidial fovea small and circular, occupying 21% of corresponding body diameter and located far posterior to the anterior end (3.9 times the head diameter of the anterior end). Protruding corpus gelatum not observed. Morphologies and distribution patterns of cervical and somatic setae are similar to the male. Jointed ventral seta located just behind the pharynx absent. Buccal cavity, teeth and pharynx similar to that of male. Bulb occupying 74% of corresponding body diameter. Nerve ring situated at 67% of the pharynx length, from anterior end. Vulva located 411 µm from anterior end, at 62% of body length. A pair of ventral papillae surround the vulva. Reproductive system didelphic-amphidelphic, with outstretched ovaries. Anterior and posterior ovary to right side of intestine. Tail conical (67 µm long), similar to the male.

Diagnosis. Ixonema gracieleae sp. nov. it is characterized by its finely striated cuticle. Amphidial fovea small and circular located far posterior to the anterior end. Protruding corpus gelatum not observed. Rows of cervical and somatic setae on peduncles along the body. Reproductive system with two opposed and outstretched testes in the males and didelphic-amphidelphic, with outstretched ovaries in the females. Spicules curved and gubernaculum without apophysis. Four setiform ventral supplements: three precloacal setae (the two closest to the cloaca are jointed and the furthest apparently non-jointed) and a jointed ventral seta located just behind the pharynx. Tail conical with a blunt tip where the three caudal glands open through separate outlets into papilla-like extensions.

Differential diagnosis. Ixonema gracieleae sp. nov. resembles the monospecific genus Bathynox (Bussau, 1993) Bussau & Vopel, 1999 due to the presence of the setae on peduncles distributed along the whole body. However, I. gracieleae sp. nov. differs from Bathynox in having three caudal glands opening through separate outlets in papilla-like extensions (vs three glands opening in a single outlet in Bathynox). Furthermore, the male reproductive system is different between the genera: male diorchic in I. gracieleae sp. nov. vs male monorchic in Bathynox and the gubernaculum lacks apophysis in I. gracieleae sp. nov. vs the presence of dorsal apophysis in Bathynox.

The presence of setae on peduncles in I. gracieleae sp. nov. differentiates it from other species of the genus. The new species shares the presence of a single jointed ventral seta located just behind the pharynx with I. powelli, as well as jointed precloacal setae in the males. Nonetheless, I. gracieleae sp. nov. differs from I. powelli in terms of the shape of the amphidial fovea (circular in I. gracieleae sp. nov. vs pocket-like in I. powelli), the distribution pattern and number of rows of cervical setae (6 rows of cervical setae in I. gracieleae sp. nov. vs 4 rows of cervical setae I. powelli) and gubernaculum length (11.5–14.5 µm in I. gracieleae sp. nov. vs about 6 µm in I. powelli).

Ixonema gracieleae sp. nov. differs from I. sordidum in having long somatic setae alternating with short somatic setae along the body and due to the presence of precloacal supplements, these characteristics are absent in the mentioned species. I. gracieleae sp. nov. differs from I. deleyi in terms of the presence of the gubernaculum (vs absent in I. deleyi) and the number and morphology of supplements (jointed ventral seta located just behind the pharynx + two jointed setae closer to the cloaca and a smaller non-jointed seta further away in I. gracieleae sp. nov. vs a single non-jointed ventral precloacal seta in I. deleyi). A comparison of the main characters of all valid species of Ixonema is presented in Table 4.

Dichotomous identification key for valid species of IxonemaLorenzen, 1971