Oxyascaris annulatum, Santos & Willkens & Silva & Melo & Fernandes, 2023

Santos, Ana Nunes, Willkens, Yuri, Silva, Luiz Fernando Neres, Melo, Francisco Tiago de Vasconcelos & Fernandes, Thayane Ferreira, 2023, A new species of Oxyascaris Travassos, 1920 (Nematoda: Cosmocercoidea) parasite of Leptodeira annulata (Serpentes: Colubridae) from Brazil, with a key to the species of the genus, International Journal for Parasitology: Parasites and Wildlife 22, pp. 243-248 : 244-246

Oxyascaris annulatum n. sp. Santos, Melo & Fernandes, 2023

Type-host: Leptodeira annulata Linnaeus, 1758

Site in host: small intestine

Type-locality: Riachao ˜, Maranh˜ao (7 ◦ 30′33.8″ S 46 ◦ 23′02.9″W)

Type-material: The holotype ( MPEG 285 ) and paratypes ( MPEG 288 ), the allotype ( MPEG 286 ) and paratypes ( MPEG 287 ) are deposited in the Museu Paraense Emílio Goeldi (MPEG) Bel´em, Par´a, Brazil .

ZooBank registration: To comply with the regulations set out in article 8.5 of the amended 2012 version of the International Code of Zoological Nomenclature ( ICZN, 2012), details of the new species have been submitted to ZooBank. The Life Science Identifier (LSID) for Oxyascaris annulatum is urn:lsid:zoobank.org:pub:3FC55064-3729-43D0-8D9A-A95B7D9665B7 .

Etymology: The name of the species is given in reference to the type host Leptodeira annulata .

Description ( Figs. 1 and 2 )

2.1. General

Evident sexual dimorphism, mature females four times larger than males in total length. Females presenting a vesicle at anterior region of body, with a wider portion beginning at cephalic region, extending to nerve ring, narrowing towards esophageal bulb ( Fig. 1E ). Oral opening at cephalic end, triangular in shape, with three lips; dorsal lip with a pair of papillae; lateroventral lips with one papilla and one amphid each ( Fig. 1B and 2A, D ). Esophagus divided into pharynx, corpus, isthmus and bulb ( Fig. 1B, E ). Nerve ring at posterior third of esophagus in males and at middle of esophagus in females ( Fig. 1B, E ). Excretory pore postbulbar or at the bulb level in males and pre-bulbar in females ( Figs.1B, E and 2E ). Numerous somatic papillae present at cuticular surface in both sexes, randomly distributed ( Fig. 2E ). Discrete lateral line in females ( Fig. 2C ), absent in males. Tail conical, robust, tapering abruptly to a short filament in both sexes ( Figs. 1C, G and 2C, F ).

2.2. Males (based on the holotype and 6 paratypes)

Total body length 5.5 mm (3.8–5.7 mm; 5.08) mm, body width at level of esophagus-intestinal junction 179 (116–202; 168). Esophagus 434 (387–547; 463) long; pharynx 42 (37–55; 45) × 47 (37–47; 42), corpus 324 (314–418; 361) × 53 (53–79; 59); isthmus 47 (32–79; 50) × 42 (36–47; 40), bulb 66 (66–84; 75) × 68 (58–76; 72) respectively. Nerve ring at 253 (166–284; 242) and excretory pore 550 (390–518; 471) from anterior end, respectively. Caudal papillae slightly larger in size than somatic papillae, 17 in total (3 + 1:1:3): three pairs of ventral precloacal papillae; one large unpaired medial precloacal papilla at anterior border of cloacal aperture ( Fig. 2G ); one pair of ventral adcloacal papillae ( Fig. 2G ); three pairs of postcloacal papillae (the first postcloacal pair ventral, the second lateroventral, and the third pair ventral) ( Fig. 1C and 2F, G ). Two small lateral phasmids located at tail tip. Spicules curved distally, right spicule 149 (84–174; 137) and left spicule 184 (120–180; 152) long ( Fig. 1D ). Gubernaculum absent. Tail 287 (234–334) long ( Fig. 1C and 2F ).

2.3. Female (based on allotype and 4 paratypes)

Total body length 22 mm (18–24; 21), body width at level of esophagus-intestinal junction 295 (213–350; 272). Esophagus 668 (739–929; 802) long; pharynx 68 (53–74; 62) × 74 (58–74; 64); corpus 666 (571–724; 637) × 129 (100–132; 124); isthmus 58 (26–108; 64) × 73 (63–73; 70); bulb 124 (92–105; 99) × 118 (108–139; 120). Nerve ring at 347 (276–418; 342) and excretory pore at 634 (516–671; 579) from anterior end, respectively. Vulva pre-equatorial, lips not protruded ( Fig. 2B ), located at 8 mm (6.4–8.2, corresponding 34–35% of the total body length; 7.3) from anterior end. Didelphic and amphidelphic genital apparatus. Vagina muscular, directed anteriorly, flexed to posterior region throughout most of length, giving rise to one uterine branche directed anteriorly and one branch directed posteriorly. Uterine branches associated with an ovary each. Anterior and posterior region of uterus branch with a dilated portion, flexed posteriorly, usually filled with spermatozoa ( Fig. 1F, H ). Body width at the level of vulva 547 (500–639; 576). Eggs oval, often larvated 82 (82–103) long and 66 (65–68) wide ( Fig. 1I ). Tail 1 mm (0.974–1.1 mm; 480) long ( Fig. 1F ; 2C ).

3. Remarks

We assigned the nematodes presented in this study to the Cosmocercidae by the evident sexual dimorphism compared to other cosmocercid genera, primarily the total length of females (mature females more than twice as large as males). Additionally, the nematodes have three distinct lips, females didelphic amphidelphic, uteri with one branch directed anteriorly and one posteriorly filled with numerous small eggs; tail conical robust, males without pre-anal pseudosucker. According to Travassos (1920), Freitas (1958), and Bursey and Goldberg (2007), those morphological traits can be attributed to species of the genus Oxyascaris .

The species of this genus are distinguished based on a combination of the following morphological characters: presence or absence of unpaired medial papillae located at the anterior cloacal lip, the number and distribution of caudal papillae, the presence or absence of lateral body alae in males and females, presence or absence of gubernaculum, length of spicules in males, and position of the vulva relative to the anterior end of the body in females ( Freitas 1958; Baker and Vaucher 1985; Bursey and Goldberg 2007).

Oxyascaris comprises six known species: Oxyascaris caatingae , O. caudacutus , O. oxyascaris , O. similis , O. longum and O. mcdiarmidi ). The new species is distinguished from O. mcdiarmidi by the absence of the gubernaculum (present in O. mcdiarmidi ) and the presence of an unpaired papilla on the upper lip of the cloaca (absent in O. mcdiarmidi ). The new species is similar to O. oxyascaris by lacking gubernaculum, but differs by the presence of the unpaired papilla on the upper lip of the cloaca ( Freitas, 1958; Bursey and Goldberg, 2007; Felix-Nascimento et al., 2020; Alcantara et al., 2021; Santos et al., 2023).

The new species shares the presence of an unpaired papilla at the anterior cloacal lip with O. caatingae , O. caudacutus , and O. similis . However, Oxyascaris annulatum n. sp. differs from O. caatingae by the total number of caudal papillae pairs (7 pairs + 1 unpaired vs 15 pairs + 1, respectively), as well as in the distribution of papillae (3:1:3 vs 5:1: 9 in O. caatingae , papillae distribution formula pre-: ad-: post-cloacal). Additionally, the males of the new species lack gubernaculum, while it is present in males of O. caatingae ( Felix-Nascimento et al., 2020) .

The males of Oxyascaris annulatum n. sp. and O. caudacutus do not have gubernaculum (based on Freitas, 1958). However, they differ in the total number of papillae pairs (7 pairs + 1 vs 13 pairs + 1 in O. caudacutus ), and the distribution of papillae (3:1:3 vs 6:0: 7 in O. caudacutus ) and also by females with a discreet lateral line in the new species (wide lateral alae in O. caudacutus ). Additionally, the new species is larger than O. caudacutus (males: 3.8–5.7 mm and females: 18–24 mm vs males: 2.78–3.62 mm and females: 5.63–16.21 mm, respectively). In both species, the vulva is located in the pre-equatorial region of the body. Still, they differ in the distance of the vulva from the anterior region (6.4–8.2 mm, corresponding 34–35% of the total body in the new species vs 2.01–5.33, corresponding 25–32% of the whole body in O. caudacutus ) ( Freitas, 1958).

The new species resembles O. similis by the absence of the Gubernaculum, but they can be easily distinguished by a discrete lateral line in females of O. annulatum n. sp., while in O. similis the lateral alae is present in both sexes, and they differ by the number and distribution of caudal papillae pairs (7 + 1/3:1: 3 in the new species vs 13 + 1/6:0: 7 in O. similis ). The position of the vulva differs in both species (6.4–8.2 mm, corresponding 34–35% of the total body in the new species vs 3.52–14.07 mm, corresponding 43–51% of the whole body in O. similis ), as well as the position of the nerve ring in males and females (males: 166–284 and females: 276–418 in Oxyascaris n. sp. vs males: 270–460 and females: 310–700 in O. similis ) ( Freitas, 1958).

Oxyascaris longum was originally described as Aplectana longa , and in a recent study conducted by Santos et al. (2023) (in press), the species was reallocated into the genus Oxyascaris . Therefore, the new species differs from O. longum by the absence of a gubernaculum (present in O. longum ), the presence of discrete lateral alae (lateral line) in O. annulatum n. sp. (absent in O. longum ), and the pattern of caudal papillae, which in the new species is 3:1:3 + 1, whereas, in O. longum , it is 9:0:6 + 1. Additionally, O. annulatum n. sp. has a pre-equatorial vulva; in O. longum , the vulva is equatorial ( Alcantara et al., 2021).

Figures

Fig. 1. Line drawings of Oxyascaris annulatum n. sp. A – Male, whole view; B – Male, anterior end, lateral view; C – Male, ventral view of tail; D – Male, spicules; E – Female, anterior end, lateral view; F – Female, reproductive system; G – Female, tail, lateral view; H – Female, detail of uterine dilation; I – Larvated egg. Scale bars – A, F, H: 350 μm; B, E: 250 μm; C, G: 150 μm; D, I: 50 μm.

Fig. 2. Scanning Electron Microscopy of O. annulatum n. sp. A – Female, anterior end, detailing cephalic papillae (arrowhead), apical view; B – Female, vulva (vu), ventrolateral view; C – Female, posterior end, anus (an) and lateral line (l); D – Male, anterior end apical view, cephalic papillae (arrowhead) and amphid (arrow); E – Male, detail of excretory pore (ep) and somatic papillae (arrowhead); F – Male, posterior end, precloacal papillae (arrowhead), unpaired papilla (arrow), insert – adcloacal papillae (arrowhead), and detail of unpaired papilla (p). Scale bars – A: 20 μm; B, F: 100 μm; C: 200 μm; D: 10 μm; E: 50 μm; insert: 20 μm.