Characithecium chascomusensis ( Suriano, 1981 ),

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: 384-386

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Characithecium chascomusensis ( Suriano, 1981 )

n. comb.

Characithecium chascomusensis ( Suriano, 1981)  n. comb.

( Figs. 1–8View FIGURES 1 – 8; 43–44)

Type host. Cyphocharax voga (Hensel) 

Type locality. Chascomús Lake, 35 ° 37 ’S, 58 ° 04’ W, Chascomús, Buenos Aires province, Argentina.

Other host. Oligosarcus jenynsii (Günther)  .

Other localities. Nahuel Ruca Lake, 38 °08´S, 57 ° 32 ´W, Mar Chiquita, Buenos Aires Province, Argentina.

Synonyms: Androspira chascomusensis  Suriano, 1981; Palombitrema chascomusense ( Suriano, 1981) Suriano, 1997

Prevalence. 100 %.

Mean abundance (intensity range). 36 (2–163).

Type material. Voucher s pecimens (MLP-He- 6803) were deposited in the Helminthological Collection of the Museo de La Plata ( HCMLP), La Plata, Argentina.

Redescription. Based on 20 specimens. Body robust, 611 (480–754; n = 20) long; greatest width 196 (137–277) usually at middle of body. Two pairs of cephalic lobes, 1 lateral and 1 anterior pair divided into 3 lobules. Five pairs of head organs and cephalic glands present. Four eyespots, frequently dissociated, accessory granules often present in cephalic region and anterior to pharynx. Pharynx ovate, muscular 43 (33–48) in greatest width; esophagus short to moderately long. Haptor sub-hexagonal, 85 (71–89) long, 113 (100–132) wide. Ventral anchor 40 (31–44) long, base 26 (20–28) wide; with elongate superficial root, short deep root, straight shaft and curved distal point. Dorsal anchor 36 (27–42) long; base 22 (16–23) wide; with well-developed roots, straight shaft and curved distal point. Ventral bar 36 (30–46) long, with medial suture with expanded ends. Dorsal bar widely Ushaped, 40 (37–49) long, with slightly enlarged ends. Hooks similar in shape; pairs 1 and 5 reduced in size 16 (13–19) long, hooks (excluding pairs 1 and 5) 23 (16–28) long, with protruding thumb and delicate point; shank comprised of 2 subunits; proximal subunit expanded, filamentous hooklet (FH) loop extending anterior to union of shank subunits. MCO a coiled tube with 3–4 counterclockwise coils, 237 (216–254) long; base of MCO reelshaped, connected to articulation process of accessory piece. Accessory piece 33 (29–40) long, clamp-shaped, comprising 2 subunits connected by a muscular ligament, distal subunit claw-like, proximal subunit larger, subtriangular, with short and slightly concave free distal extreme serving as guide for MCO. Articulation process of accessory piece twisted. Gonads overlapping; testis dorsal to germarium; seminal vesicle a distal dilation of vas deferens, looping before entering base of MCO; single, prostatic reservoir present. Vitellaria moderately dense throughout trunk, except in regions of reproductive organs; oviduct, ootype and uterus not observed.Vaginal aperture strongly sclerotized and sinistral; vagina a long and tortuous sclerotized tube, directed posteriorly and convoluted before connecting with seminal receptacle. Seminal receptacle, medial and anterior to germarium. Eggs not observed.

Remarks. A detailed morphological examination of the specimens newly collected from O. jenynsii  from both, the type locality and Nahuel Rucá Lake, and their comparison with the descriptions provided by Suriano (1981; 1997) showed that all are members of the same taxon by having identical morphology of MCO, accessory piece, hooks and internal organs. It is noteworthy that no type material is available for this species, which was originally described as Androspira chascomusensis  by Suriano (1981) and later transferred to Palombitrema chascomusense by the same author ( Suriano 1997). However, the morphology of the MCO and hooks does not agree with the diagnosis of Palombitrema Price & Bussing, 1968 to which the species was assigned by Suriano (1997). Palombitrema is characterized by having the MCO directly articulated to the accessory piece, pairs 6 and 7 of hooks different in shape than hooks 1–5, being the pair 7 also considerably larger, and dorsal anchors with little developed roots and larger than ventral anchors. ( Price & Bussing 1968; Kritsky & Leiby 1972; Kritsky & Thatcher 1974; Mendoza Franco et al. 1999; 2003; 2009).In contrast, in our specimens, the MCO is articulated by a ligament to accessory piece, hooks are of similar shape and length and anchors have developed roots. These characteristics that clearly differentiate Palombitrema from Characithecium, were not considered in the resurrection of Palombitrema by Suriano (1997), indicating that the inclusion of specimens from C. voga  and O. jenynsi  in this genus was erroneous. Consequently, this species is transferred to Characithecium as C. chascomusensis  n. comb.

Characithecium chascomusensis  n. comb. can be readily differentiated from C. costaricensis  , the only member of the genus, by the morphology of the accessory piece, the number of coils in the MCO (3–4 in C. chascomusensis  n. comb. vs ½ – 1 in C. costaricensis  ), the position of vaginal aperture (lateral in C. chascomusensis  vs midventral in C. costaricensis  ) and the absence of a posterior ventral projection in the ventral bar as present in C. costaricensis  . Furthermore, C. chascomusensis  n. comb. can be distinguished from its other congeners herein described by possessing a higher number of coils in the MCO; by having the vaginal aperture located anteriorly, at level of the prostatic reservoir; and by the shape of the accessory piece, with a pointed claw-like distal subunit and a subtriangular proximal subunit, latter with short and slightly concave free distal extreme.