Characithecium longianchoratum, 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 genus, Zootaxa 3893 (3), pp. 382-396 : 386-388

Characithecium longianchoratum n. sp.

(Figs. 9–17; 45–46)

Type host. Oligosarcus jenynsii (Günther)

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

Prevalence. 100%.

Mean abundance (intensity range). 20.8 (2–98).

Type material. Holotype (MLP-He-6795) and paratypes (MLP-He-6796) are deposited in the Helminthological Collection of the Museo de La Plata ( HCMLP), La Plata, Argentina.

Etymology. The specific name is refers to the large size of ventral anchors.

Description. Based on 20 specimens. Body small and delicate, 450 (351–540; n =20) long; greatest width 144 (104–181) usually at middle of body. Two pairs of cephalic lobes, 1 lateral and 1 anterior. Four pairs of head organs observed. Cephalic glands present. Four eyespots, frequently dissociated, accessory granules often present in cephalic region and anterior to pharynx. Pharynx spherical, muscular 32 (25–38) in diameter; esophagus short. Haptor 110 (93–134) wide, 60 (50–70) long. Ventral anchor 56 (51–61) long, base 24 (20–26) wide; with welldeveloped roots, superficial root elongate, deep root shorter, shaft long and curved, curvature more pronounced at distal tip; anchor filament conspicuous. Dorsal anchor 34 (30–38) long, base 22 (19–25) wide, with well-developed roots, straight shaft and curved distal point. Ventral bar 43 (39–56) long, with slight antero-medial projection, medial suture and expanded ends. Dorsal bar curved, 33 (28–43) long, with expanded ends. Hooks similar in shape; pairs 1 and 5 reduced in size 18 (16–19) long, hooks (excluding pairs 1 and 5) 26 (18–37) long, with protruding thumb and delicate point; shank comprised of 2 subunits; proximal subunit expanded, FH loop extending anterior to union of shank subunits. MCO a coiled tube with 2 counterclockwise coils, 144 (123–176) long, base of MCO reel shaped, connected to articulation process of accessory piece. Accessory piece 26 (24–28) long, clamp-shaped, comprising 2 subunits with sharp distal ends, proximal subunit larger and serving as guide for 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 moderately dense throughout trunk, except in regions of reproductive organs. Oviduct, ootype and uterus not observed. Vaginal aperture poorly sclerotized, sinistroventral; vagina as a sclerotized tube connecting with large and globose seminal receptacle. Seminal receptacle, medial and anterior to germarium. Egg 55 long, 45 wide, spherical yellow brown bearing a short polar filament with bifurcate end.

Remarks. Characithecium longianchoratum n. sp. can be differentiated from C. costaricencis by the morphology of accessory piece, the number of coils of the MCO (2 in C. longianchoratum 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 absence of a posterior ventral projection in ventral bar. Furthermore, C. longianchoratum differs from its congeners herein described by having a poorly sclerotized and sinistroventral vaginal pore; by the shape of the accessory piece with both distal and proximal subunits with pointed tips; by having a ventral bar with sub-quadrate elongated ends; and by having a long and curved shaft in the ventral anchor.

The distally pincer-shaped accessory piece and the shape of anchors of the new species show some resemblance to Urocleidoides strombicirrus ( Price & Bussing,1967) Kritsky & Thatcher, 1974 .This species was considered as incertae sedis by Kritsky et al. (1986) in their revision of Urocleidoides . Since then, no generic reassignment has been made for U. strombicirrus , despite it has been reported later parasitizing Astyanax spp. from Colombia, Nicaragua and Panama ( Mendoza-Franco et al. 2003, 2009). Mandoza-Franco et al. (2003) suggest that it species may constitute a new genus. The extended diagnosis of Characithecium could now include U. strombicirrus , however more studies are necessary for confirm their generic status, especially because the MCO is apparently directly articulated to the accessory piece (see Price & Bussing 1967; Kritsky & Thatcher 1974; Mendoza-Franco et al. 2003; 2009). Nevertheless, although U. strombicirrus could in the future be transferred to Characithecium, being readily distinguished from C. longianchoratum by its smaller size and by having a lateral and heavily sclerotized vaginal aperture ( Price & Bussing 1967; Kritsky & Thatcher 1974; Mendoza-Franco et al. 2003; 2009).