Araguanema mutabile, Ivanova, 2016

Ivanova, Elena S., 2016, Araguanema mutabile sp. nov., a new species of a rare genus (Drilonematoidea: Cephalobomorpha) parasitic in earthworms of Ecuador, Revue suisse de Zoologie 123 (2), pp. 253-258 : 254-257

Araguanema mutabile sp. nov.

Figs 1 & 2

Type specimens: Holotype female (catalogue number MHNG-INVE-92679 ) and a paratype female ( MHNG- INVE-92681 ) deposited in the Muséum d’histoire naturelle, Geneva, Switzerland.

Diagnosis: Araguanema mutabile sp. nov. is characterised by the presence of somatic sensory organs of two types, the different number of fimbriate organs in different specimens, four cephalic papillae, a short, widened, cuticularised stoma, inconspicuous amphids, a muscular, clavate pharynx with the long corpus expanded at anterior, an isthmus and a basal bulb, a nerve ring encircling isthmus, no distinct spermatheca, a posterior position of vulva, eggs with thick, faintly-coloured egg-shells, and a wide anus with long protruding fibres. Males unknown. It was assigned to the genus Araguanema Ivanova & Hope, 2004 on the basis of the presence of somatic sensory organs of two types, four cephalic sensilla, a muscular pharynx, a nerve ring position anterior to the pharynx bulb, the similarly structured reproductive system without a differentiated spermatheca, the similar vulva position and similar, characteristic structure of anus. It closely resembles A. venezuelae Ivanova & Hope, 2004 , the only other known species of the genus, in general appearance and body proportions and the structure of sensory organs. The new species is distinguished from A. venezuelae by the differently shaped pharynx (vs cylindrical with the slight basal swelling), inconspicuous vs prominent amphids, a different stoma structure (vs shallow, infundibilar, non-cuticularised), more numerous eggs with ornamented vs smooth egg-shells and the different arrangement of the sensory organs (more numerous, larger fimbriate organs and vesicular organs arranged in one file vs two files).

Other genera of Diceloidinae include Diceloides Timm, 1967 and Mbanema Spiridonov, 1992 ( Timm, 1967; Spiridonov, 1992). The former genus was described from the glossoscolecid host Thamnodrilus yunkeri Gates, 1968 from Panama ( Timm, 1967). Male morphology is unknown for Diceloides as well as Araguanema . The original description of Diceloides was also based mostly on females because the only male specimen obtained was incomplete, lacking the tail end. The general morphology of Diceloides and Araguanema is similar in the structure of a head end, the female reproductive system and the presence of two types of sensory organs of a lateral field, fimbriate and vesicular. The main diagnostic feature for these genera is the position of a nerve ring which is located on an intestine in Diceloides , but on pharynx in Araguanema . Timm (1967) also reported the presence of an offset spermatheca in Diceloides which is absent in Araguanema . Mbanema nigeriense Spiridonov, 1992 was recovered from the earthworm Eudrilus eugeniae ( Kinberg, 1867) (Eudrilidae) from Nigeria ( Spiridonov, 1992). It is differentiated from the other genera of Diceloidinae in having the sensory organs of the only type - vesicular ones ( Spiridonov, 1992). The salient spermatheca was also reported.

The different number of fimbriate organs in both specimens described below remains unexplained and calls in question the credibility of this trait for the species identification within Araguanema . For both species of this genus, the different disposition of fimbriate organs on left and right body sides was noted while their number remains unknown ( Ivanova & Hope, 2004).

Etymology: The species name refers to the variability in the number of fimbriate organs.

Description

Female: Short, stout nematode. Body tapered to both ends. Head end bluntly rounded. Tail broadly conical. Short conical mucron 3-4 μm long present. Cuticle 2-3 μm thick, distinctly annulated (annuli ca. 2 μm wide). Lateral chords stretched from short distance from apex to nearly to tail tip, ca. 20 (19-23) μm wide. Left lateral chord of holotype bearing irregular row of vesicular sensory organs (VO) broken by large, prominent fimbriate organs (FO) ( Fig. 1A, E, F ). VO 6-9 μm in diam., with shallow cavity and seta inside observed only in portion of organs. VO arranged in one disorderly file with interval between them 2-6 μm and located in the middle of lateral chord at body ends but slightly displaced dorso-laterally at midbody. Total number of VO exceeding one hundred. Six FO present: anteriormost in 80 μm from apex; second in 300 μm from it or at the level of ovary reflexion; third in 370 μm posteriad; fourth in 190 μm further away; fifth just anterior to vulva level; sixth at mid-tail. Each FO crater-like, convex, radially striated, 32±4 (27-36) μm in basal diam., with an aperture 7±2 (5-9) μm in diam. and a single protruding sensillum; flanked by smaller vesicular organs 2-5 μm in diam. On the right lateral chord, the anteriormost and posteriormost FO located closely to body ends.

In the paratype, 24 FO positioned along lateral chord anterior to anus between VO in a pattern similar to the holotype, distanced from each other in 78±10 (65-90) μm. Additionally, 2 FO located very slightly asymmetrically in caudal region in 120 μm from tail tip ( Fig. 1G ); all FO of paratype slightly smaller than those in holotype: 24±3 (21-28) μm in basal diam. and aperture 7±3 (3-10) μm in diam.

Mouth aperture small. Lips absent. Four bristle-like sensilla slightly distanced from mouth aperture. Amphids not detected. Stoma small, bowl-shaped, cuticularised, with walls ca. 1 μm thick ( Fig. 1B ); in paratype straighter than in holotype ( Fig. 1C ). Pharynx ( Figs 1C ; 2A ) extending to anterior end, muscular, clavate, with long corpus expanding towards anterior, short, not demarcated morphologically isthmus and small pyriform basal bulb. Corpus 34 μm wide at anterior in holotype, 24 μm in paratype; isthmus 20 μm wide, bulb 20 μm wide and 27 μm long. Nerve ring encircling isthmus. Excretory pore in holotype located opposite nerve ring in dorsolateral position ( Fig. 1A ); not detected in paratype. Cardia small. Intestine with thickened walls and darkish content. Reproductive system monodelphic, prodelphic. Ovary tip situated between vulva and anus in holotype, posterior to anus in paratype. Ovary 34 μm wide distally, oocytes initially numerous, then placed in two, than one row. Mature oocytes large, with thick walls. Ovary running to anterior by dorsal body side and reversing at short distance from pharynx base. Spermatheca not demarcated. Oviduct indistinct. Up to 17 eggs in thinwalled uterus. Eggs ovoid, with egg-shells ca. 2 μm thick covered by minute tubercles divided by shallow grooves ( Fig. 1H, I ). Egg-shells and proximal part of ovary with ink-bluish colouration ( Fig. 2B ). Vagina short (18 μm), slightly inclined, directed posteriad ( Fig. 1D ). Vulval lips very slightly enlarged. Vulva posterior. Anus at a short distance to vulva, rectum a large chamber with numerous long, hair-like fibres protruding from anus ( Fig. 2C ). Anus position in paratype obscured and was estimated approximately. Rectal glands not detected.

Dimensions

Holotype female (broken): L = 1518 μm; max width = 100 μm; anal width = 51 μm; Ph = 147 μm; Ex = 128 μm; NR = 125 μm; anterior to ovary flexure = 268 μm; V% = 81.4; egg 74 μm x 40 μm; tail length = 154 μm; a = 15.2; b = 10.3; c = 9.9.

Paratype female: L = 1953 μm; max width = 105 μm; anal width = 69 μm; Ph = 153 μm; anterior to ovary flexure = 370 μm; V% = 81.3%; egg = 67 μm x 41 μm; tail length = 135 μm; a = 18.6; b = 12.8; c = 14.5.

Type habitat: Anterior region of coelomic cavity.

Type host and locality: Aptodrilus fuhrmanni ( Michaelsen, 1918) , (Annelida, Clitellata, Lumbricina, Glossoscolecidae ), MHNG-INVE-92020 , Ecuador, Prov. Bolivar, Cashka Totoraz , 3200 m Paramo , 03.04.1987. See Zicsi (1988) for description of these specimens.

Remark: The description is based mainly on the holotype female, which is in lateral position with the left side on top. The details of morphology of the right side of body (particularly, the number of fimbriate organs) were traced only on body ends due to the significant body thickness. The anterior part of the paratype female is positioned similarly while the posterior is in the subventral position. The condition of the paratype did not allow locating an excretory pore.

Figures

Fig. 1. Araguanema mutabile sp. nov. Female. A, B, D-F, H-I: holotype; C, G: paratype. Except G, all in lateral position. Scale bars in μm. (A) Entire worm. (B) Head. (C) Anterior part. (D) Vulval region. (E-F) Lateral chord at mid-body. (G) Tail, subventral view. (H-I) Egg-shell. Abbreviations: FO ‒ fimbriate organ, VO ‒ vesicular organ.

Fig. 2. Araguanema mutabile sp. nov. Female holotype, all from lateral, scale bars in μm. (A) Anterior part. (B) Region of anus. (C) Egg in uterus.