Characithecium robustum, Rossin, María Alejandra & Timi, Juan Tomás, 2014

Rossin, María Alejandra & Timi, Juan Tomás, 2014, Characithecium (Monogenoidea: Dactylogyridae) parasitic on the Neotropical fish Oligosarcus jenynsii (Teleostei: Characidae) from the Pampasic region, Argentina, with the emendation of the gen, Zootaxa 3893 (3), pp. 382-396: 388-390

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Characithecium robustum

n. sp.

Characithecium robustum  n. sp.

( Figs. 18–26View FIGURES 18 – 26; 47–48)

Type host. Oligosarcus jenynsii (Günther)  .

Type locality. Nahuel Rucá 38 °08´S, 57 ° 32 ´W, Mar Chiquita, Buenos Aires Province, Argentina.

Prevalence. 70 %.

Mean abundance (intensity range). 1.8 (1–7).

Type material. Holotype (MLP-He- 6797) and paratypes (MLP-He- 6798) are deposited in the Helminthological Collection of the Museo de La Plata ( HCMLP), La Plata, Argentina.

Etymology. The specific name is derived from Latin robustus  (=robust) and refers to the larger size of this species in relation to the other species in the genus.

Description. Based on 11 specimens. Body robust 842 (606–1000; n = 10) long; greatest width 236 (186–282) usually at middle of body. Cephalic lobes developed. Five pairs of head organs and cephalic glands present. Four eyespots in cephalic region and anterior to pharynx, accessory granules present in cephalic regions posterior to pharynx. Pharynx spherical, 47 (40–59) in diameter; esophagus moderately long. Haptor hexagonal, 81 (67–92) long, 114 (100–128) wide. Ventral anchor 43 (39–48) long, base 29 (26–32) wide, with superficial root well developed and elongated, short deep root, straight shaft and curved distal point; anchor filaments conspicuous. Dorsal anchor 35 (32–37) long, base 25 (21–27) wide, with developed roots, similar in shape to ventral anchor. Ventral bar 30 (27–34) long, V-shaped, with medial suture and slightly dilated extremes. Dorsal bar 35 (31–38) long, U-shaped, with curved convex margin, straight concave margin and expanded ends. Hooks similar in shape, pairs 1 and 5 reduced in size 17 (11–20) long, hooks (excluding pairs 1 and 5) 22 (17–24) long, with protruding thumb and delicate point; shank comprised of 2 subunits; proximal subunit expanded, FH loop short. MCO a coiled tube with 2 ½ counterclockwise coils, 231 (216–240) long; base of MCO reel- shaped, connected to articulation process of accessory piece. Accessory piece 28 (22–30) long, pincer-shaped, comprising 2 subunits connected by a muscular ligament, distal subunit with bifurcate end; proximal subunit larger, with concave free distal extreme serving as guide of MCO. Gonads overlapping; testis dorsal to germarium; seminal vesicle as a distal dilation of vas deferens, looping before entering base of MCO. Prostatic reservoir present. Vitellaria dense throughout trunk, except in regions of reproductive organs. Oviduct, ootype and uterus not observed. Vaginal aperture ventro-sinistral sclerotized and funnel-shaped. Vagina a sinuous sclerotized tube connecting with a sclerotized vaginal vestibule leading to a seminal receptacle anterior to germarium. Egg 78 long x 50 wide, brownish, triangular, bearing short bipolar filament.

Remarks. Characithecium robustum  n. sp. is the largest member of the genus and can be distinguished from C. costaricensis  , by the morphology of accessory piece, the number of coils of MCO (2 ½ in C. robustum  n. sp. vs ½ – 1 in C. costaricensis  ), the position of the vaginal aperture (latero ventral vs midventral), the sclerotization of the vaginal canal and the absenceof a posterior ventral projection in ventral bar. Furthermore, C. robustum  differs from the new species here described by having a sclerotized vaginal vestibule, as well as a V-shaped ventral bar, and by the shape of the accessory piece, with distal subunit with bifurcate end.