Orientatractis brycini, David González-Solís & Jean Mariaux, 2017

David González-Solís & Jean Mariaux, 2017, Orientatractis brycini sp. nov. (Nematoda: Atractidae) from characiform freshwater fishes in Gabon, Africa, Revue suisse de Zoologie 124 (1), pp. 1-8 : 2-7

Orientatractis brycini sp. nov.

Figs 1-3

Deposition of specimens: Holotype (MHNG- INVE-91071), allotype (MHNG-INVE-91072) and paratypes (MHNG-INVE-91073) in the Muséum d’histoire naturelle, Geneva. – Paratypes in the Helminthological Collection of the Institute of Parasitology, Biology Centre, Czech Academy of Sciences, Č eské Bud ĕ jovice (Cat. No. N-1072).

Type host: Brycinus macrolepidotus Valenciennes ( Alestidae , Characiformes ) (Body length 21.4 cm).

Other host: Xenocharax spilurus Günther ( Distichodontidae , Characiformes ) (Body length 15.5-20.2 cm).

Site of infection: Intestine.

Type locality: Bridge on Ogooué River, Haut-Ogooué, Gabon (01°38’24”S; 13°31’48”E; elev. 300 m), collected on 28/11/2010.

Other localities: Mpassa River , near Hotel Poubara, Franceville, Haut-Ogooué, Gabon (01°37’12”S; 13°36’00”E; elev. 300 m), 30/11/2010.

Prevalence and intensity: Brycinus macrolepidotus : prevalence 25% (1 fish infected/4 examined), mean intensity 24 nematodes (range 24). Xenocharax spilurus : 43% (3/7), 4.3 (2-8).

Etymology: The specific name relates to the generic name of the fish host (i.e., Brycinus ).

Description

General: Whitish, small-sized nematodes, with cuticle finely transversely striated. Anterior end rounded, posterior end with very slender, long, pointed tail ( Fig. 1 A, E). Oral opening rhomboid or quadrangular, with 2 lateral and 4 submedian poorly-developed lips ( Figs 1 D, 2A, B). Each submedian lip bearing one large spherical papilla and external pair of well-sclerotized, recurved, pointed spines joined at the base and a single large median spine. Lateral lips supporting large amphids; two small spines posterior to each amphidial pore present ( Figs 1 D, 2A-D). Lateral grooves extending from first third of esophagus to posterior end of body, but not reaching tail tip ( Figs 1 E, G, 2F). Esophagus divided in a cylindrical corpus, elongated isthmus, and posterior, well-developed, valved bulb ( Fig. 1 A, B). Nerve ring surrounding isthmus at its anterior end. Deirids small, knob-like, somewhat anterior or at level of nerve ring ( Figs 1 A, B, 2E). Excretory pore anterior to esophageal bulb ( Fig. 1 A, B). Intestine straight. Rectum a hyaline tube.

Male (22 specimens, measurements of holotype in parentheses): Length of body 2.58-3.07 (3.04) mm, maximum width 52-93 (72). Length of corpus 130- 163 (150), of isthmus 289-346 (305); entire esophagus 436-507 (455). Width of esophageal bulb 33-47 (43). Nerve ring, excretory pore, and deirids 162-226 (178), 294-350 (310), and 175-199 (189), respectively, from anterior end of body. Eight pairs of caudal papillae: 1 subventral precloacal pair, 3 subventral adcloacal pairs, close to each other (one pair anterior to cloacal opening, one at same level and one posterior to it), 4 postcloacal pairs (first pair of postcloacals lateral, second and third pairs subventral and close to each other, fourth pair subdorsal) ( Figs 1 G, 3A). Pair of small, lateral outlets (probably representing phasmids) between pairs 3 and 4 of postcloacals ( Fig. 3 A, E). Single left-shifted papilla on anterior cloacal lip weakly-developed ( Fig. 3 C, D). Spicules unequal, similar, well-sclerotized. Left and right spicules 130-158 (148) and 75-90 (83) long, respectively. Both spicules with transverse striations along their lengths; proximal ends slightly expanded, distal ends sharply pointed ( Fig. 1 G, H). Gubernaculum 29-39 (37) long, well-sclerotized, proximal end rounded, with deep depression; distal end pointed and slightly ventrally curved ( Fig. 1 F). Tail 207-257 (229) long, with dorsal groove-like structure ( Fig. 3 B).

Female (13 gravid specimens; measurements of allotype in parentheses): Length of body 2.50-3.61 (3.30) mm, maximum width 60-129 (109). Length of corpus 126-170 (161), of isthmus 294-355 (318); entire esophagus 443- 509 (479). Width of esophageal bulb 34-50 (43). Nerve ring, excretory pore, and deirids 158-221 (217), 292-347 (331), and 196-205 (-), respectively, from anterior end of body. Vulva with anterior lip slightly elevated, near the posterior end of body, 2.19-3.18 (2.91) mm from anterior end of body, somewhat anterior to anal opening ( Figs 1 E, 3F). Distance anus-vulva 39-72 (44). Vagina muscular, anteriorly directed. Uterus containing fully developed larvae 673-1 176 (927) long; some females with developing eggs 236-305 × 93-110 (236-242 × 93- 94). Tail 270-388 (348) long, with pore-like phasmids between first and second thirds of tail length ( Fig. 1 E).

Remarks

Petter (1966) erected the genus Orientatractis to allocate nematodes with a particular structure of the oral opening, specifically the presence of symmetrical groups of 3 sclerotized posteriorly directed spines surrounding mouth. Currently, this genus includes 7 valid species, namely: O. asymmetrica Gibbons & Platt, 2006 in Rhinoclemmys pulcherrima Gray (Testudines) from Costa Rica, O. campechensis González-Solís & Moravec, 2004 in Paraneetroplus bifasciatus (Steindachner) (reported as Vieja bifasciata ) and Cichlasoma pearsei (Hubbs) (both Perciformes ) from Southern Mexico, O. chiapasensis González-Solís & Moravec, 2004 in Theraps intermedius (Günther) (reported as Vieja intermedia ) and Tomocichla tuba (Meek) (both Perciformes ) from Southern Mexico, O. hamabatrachos Bursey, Goldberg & Kraus, 2014 in Austrochaperina basipalmata (van Kampen) (Anura) from New Guinea, O. levanhoai (type species) in Indotestudo elongata (Blyth) (reported as Testudo elongata ) ( Testudines ) from Vietnam, O. leiperi Buckley, 1969 in Podocnemis vogli Müller (Testudines) from Colombia, and O. mekongensis Moravec, Kamchoo & Pachanawan, 2015 in Pangasius bocourti Sauvage (Siluriformes) from Thailand ( Petter, 1966; Buckley, 1969; González-Solís & Moravec, 2004; Gibbons & Platt, 2006; Bursey et al., 2014; Moravec et al., 2015). Even though the type species of the genus was not reviewed, we decided to emend the generic diagnosis, based on the already described species and present data, since several important features were not included in the original description (see Petter, 1966). Morphological features as the structure of the oral opening, presence of deirids, among others, were incorporated to the diagnosis for making it easier to distinguish Orientatractis from closely related genera (e.g., Klossinemella and Paraorientatractis ) within the Atractidae . Thus, Orientatractis and Paraorientractis have four bicornate submedian structures surrounding mouth, whereas Klossinemella shows eight pairs; the two first genera differ in the number of lips (6 vs. 4) and presence of ornamentations on the dorsal surface of body in Paraorientatractis . These changes do not modify the systematic position of the genus.

The four bicornate structures along with a pair of spines posterior to amphidial pore are only present in O. brycini sp. nov., O. hamabatrachos , and O. leiperi ; while in O. asymmetrica , O. campechensis , O. chiapasensis , O. levanhoai , O. mekongensis are lacking.

Orientatractis brycini sp. nov. shows similar body length to that of O. chiapasensis , and is near the lower size range of O. campechensis , O. leiperi and O. levanhoai , whereas the remaining three species ( O. asymmetrica , O. hamabatrachos , O. mekongensis ) have larger bodies. However, O. brycini sp. nov. differs from all species within the genus in the size of both spicules (except in O. hamabatrachos ), gubernaculum and number and distribution of caudal papillae (see Table 1 ).

The new species shares some similarities with Paraorientatractis semiannulata Gibbons, Khalil & Marinkelle, 1997 , a nematode of Podocnemis unifilis Troschel (Testudines) in Brazil ( Gibbons et al., 1997). Both species harbour identical shape and structures surrounding mouth, such as each submedian lip with a pair of recurved pointed spines and single median spine near their distal margin, along with a pair of smaller spines posterior to amphidial pores. Moreover, both have two unequal, striated spicules, similar gubernaculum and number of caudal papillae. However, they differ in the ornamentations on the dorsal surface of body and striated, broad, well-developed lateral alae in P. semiannulata .

Caballero-Rodríguez (1971) described Proatractis parvicapiticoronata from the tortoise Staurotypus triporcatus in Veracruz, Mexico. Later , this species was transferred to Klossinemella as K. parvicapiticoronata by Moravec & Thatcher (1997). González-Solís & Moravec (2004) stated that it probably belongs to Orientatractis according to the shape of spicules, number and distribution of caudal papillae and structure of the anterior end, but until the type material of K. parviticoronata is re-examined, it should be retained within the genus Klossinemella .

Interestingly, O. brycini sp. nov. was found in two fish species of the order Characiformes , but from different families ( Alestidae and Distichodontidae ) and sampling localities (Ogooue and Mpassa). Despite this, there were no differences in the morphology and biometrical values among the nematodes from both hosts, although certain morphometric variability always occurs intraspecifically. Such morphological and biometrical variability which might be associated with local ecological conditions and physiological traits of host species is not uncommon (see González-Solís & Moravec, 2004).

Nothing is known about the life cycle of these nematodes, but as in other members of Atractidae , larvae develop to the third stage in uterus, thus auto-infection is possible ( Anderson, 2000). Viviparity has greatly helped atractid nematodes to parasitize several unrelated vertebrates (i.e., turtles, fish, amphibians, grazing mammals) by venereal and oral transmission ( Baker, 1982), and to be distributed in different zoogeographical regions (America and Indonesia). The present finding represents the eighth species in the genus Orientatractis and the fourth being reported from fish hosts, since other members were reported in tortoises ( O. levanhoai , O. leiperi ), frog ( O. hamabatrachos ), and turtle ( O. asymmetrica ). This is also the first record of a species of Orientatractis in Africa, which expands the geographical distribution of the genus, since it was previously reported from Costa Rica, Colombia, Mexico (American continent), Thailand, Vietnam ( Southeastern Asia ) and New Guinea (Melanesia).

Figures

Fig. 1. Orientatractis brycini sp. nov. (A) Whole body of male, lateral view. (B, C) Anterior end of body, lateral views. (D) Cephalic end, apical view. (E) Posterior end of female, lateral view. (F) Gubernaculum, lateral view. (G) Posterior end of male, lateral view. (H) Spicules, lateral view.

Fig. 2. Orientatractis brycini sp. nov., SEM micrographs. (A, B) Cephalic end, subapical and apical views, respectively (asterisks indicate single median spine). (C) Detail of lateral lip, amphid and lateral spines, apical view. (D) Cephalic end, sublateral view (asterisks indicate single median spine). (E) Deirid. (F) Anterior end of body (arrow indicates groove-like lateral ala). Abbreviations: a ‒ amphid, b ‒ cephalic submedian papilla, ls ‒ lateral paired spine, ss ‒ submedian paired spine.

Fig. 3. Orientatractis brycini sp. nov., SEM micrographs. (A) Posterior end of male, sublateral view (arrows indicate caudal papillae). (B) Dorsal surface of male tail. (C, D) Region of cloaca, ventral views (arrow indicates left-shifted unpaired papilla). (E) Posterior end of male, lateral view (arrowhead indicates phasmids). (F) Region of anus and vulva, lateral view. Abbreviations: c ‒ anus, g ‒ groove-like dorsal structure, v ‒ vulva.

Tables

Table 1. Comparison of some selected measurements of the valid species of Orientatractis around the world; measurements are in micrometers, unless otherwise stated.

	Body length	(mm)	Spicule	length	Gubernaculum length	Caudal papillae*
	male	female	right	left
O. asymmetrica	4.1-4.3	3.7-5.5	86-104	220-239	56-66	4: 2: 3 + 1
O. brycini sp. nov.	2.6-3.1	2.5-3.6	75-90	130-158	29-39	1: 3: 4
O. campechensis	3.0-3.5	3.3-4.3	84-106	430-506	62-74	0: 5: 4 + 1
O. chiapasensis	2.7-3.0	2.0-3.8	60-68	204-238	44-49	0: 5: 4 + 1
O. hamabatrachos	3.2-4.3	3.4-4.9	79-98	146-165	55-67	2: 1: 5 + 1
O. leiperi	3.0-3.9	2.7-4.3	160	470	76	3: 1: 5 + 1
O. levanhoai	3.3	3.4	90	170	40	3: 0: 5
O. mekongensis	5.3-6.6	7.7-8.9	90-105	306-384	33-51	2: 1: 5

* pairs of caudal papillae (without considering phasmids): precloacal: adcloacal: postcloacal + single median papilla (left-shifted in O. brycini sp. nov.)