Characithecium (Monogenoidea: Dactylogyridae) parasitic on the Neotropical fish Oligosarcus jenynsii (Teleostei: Characidae) from the Pampasic region, Argentina, with the emendation of the genus Author Rossin, María Alejandra Author Timi, Juan Tomás text Zootaxa 2014 3893 3 382 396 journal article 10.11646/zootaxa.3893.3.4 b9a6a057-dd8b-4e92-8c4d-3f2bde53341e 1175-5326 227642 C8D52425-9F98-42CC-95BB-6553D943AA50 Characithecium quadratum n. sp. ( Figs. 27–34 ; 49–50) Type host. Oligosarcus jenynsii (Günther) . Type locality. Nahuel Rucá 38°08´S , 57°32´W , Mar Chiquita, Buenos Aires Province, Argentina . Prevalence. 60%. Mean abundance (intensity range). 1 (1–4). Type material. Holotype (MLP-He-6799) and paratypes (MLP-He-6800) are deposited in the Helminthological Collection of the Museo de La Plata ( HCMLP ), La Plata, Argentina . Etymology. The specific name is derived from Latin quadratum (=square) and refers to the shape of the accessory piece of the copulatory complex. Description. Based on 10 specimens . Body robust 631 (498–752; n =10) long; greatest width 174 (144–223) usually at middle of body. Cephalic lobes developed. Five pairs of head organs and cephalic glands present. Two pair of eyespots in cephalic region and anterior to pharynx, accessory granules present in cephalic regions at level of pharynx. Pharynx spherical, 36 (32–40) in diameter; esophagus short. Haptor hexagonal, 78 (71–90) long, 100 (87–114) wide. Ventral anchor 43 (40–46) long, base 28 (23–31) wide, with well-developed elongate superficial root, shorter deep root, straight shaft and curved distal point, anchor filaments conspicuous. Dorsal anchor 34 (32–36) long, base 20 (18–23) wide, with developed roots, superficial root fusiform, straight shaft with curved distal point. Ventral bar 34 (29–37) long, with medial suture flanked by 2 blunt small protrusions at posterior margin and dilated extremes. Dorsal bar curved 39 (36–41) long with ends slightly expanded. Hooks similar in shape pairs 1 and 5 reduced in size 16 (12–19) long, hooks (excluding pairs 1 and 5) 22 (19–27) long, with protruding thumb and delicate point; shank comprised of 2 subunits; proximal subunit expanded, FH loop short. MCO a coiled tube with 2 counterclockwise coils, 163 (156–171) long; base of MCO reel-shaped, connected to articulation process of accessory piece. Accessory piece large, 40 (37–45) long, comprising 2 subunits connected by a muscular ligament, distal subunit a hook-shaped; proximal subunit elongate, with expanded and cup-shaped distal end serving as guide for male copulatory organ. Gonads overlapping; testis dorsal to germarium; seminal vesicle as a distal dilation of vas deferens. Prostatic reservoir present. Vitellaria dense throughout trunk, except in regions of reproductive organs. Oviduct, ootype and uterus not observed. Vaginal aperture marginal sinistral and slightly sclerotized, opening at level of anterior border of testicle. Vagina as a sinuous sclerotized tube connecting with a seminal receptacle anterior to germarium. Remarks. Characithecium quadratum n. sp. differs from its congeners mainly by having the largest accessory piece, which is also different in shape, being rectangular with hook-shaped distal subunit and elongate proximal subunit ending in a cup-shaped anterior extreme. The position of vaginal aperture (at level of anterior margin of testicle) is also unique among congeners.