New species of Urocleidoides (Monopisthocotyla: Dactylogyridae) from Cyphocharax spilurus (Osteichthyes: Curimatidae) from the Nanay River, Peru.

Parasitological studies on Cyphocharax spp. from different regions of South America, have recorded different species of Urocleidoides Mizelle & Price, 1964 parasitizing their gills. To date, no parasites have been documented for Cyphocharax spilurus (Günther) from the Peruvian Amazonia. Thus, the main objective of the present study was to survey the monopisthocotylan parasites from the gills of C. spilurus collected in the Peruvian Amazonia. Twenty specimens of C. spilurus were collected from the Nanay River, Loreto, Peru. Parasites were removed from the gills using dissection needles and cleared in Hoyer's medium for the study of sclerotized structures. Two new species were described: Urocleidoides nanayensis n. sp. characterized by the male copulatory organ consisting in an elongated sclerotized tube forming a loop-like reservoir at its base, and an articulated accessory piece bearing a multi-pronged terminal apparatus with hook-like projections. The vaginal sclerite is can-opener-shaped, and the haptor presents unequal ventral and dorsal anchors with poorly developed roots; hooks are arranged in seven pairs: pairs I and V share a similar shape with elongated filaments, while pairs II-IV and VI-VII are composed of two subunits with straight shanks and short filaments. Urocleidoides loretoensis n. sp. is characterized by the shape of the MCO, which consists in a knife-blade-shaped with a cone-shaped base and a smoothly arched, needle-tipped sclerotized tube, and an articulated accessory piece bearing a stippled central rod with a curved branch and fan-like membranous sheath. The vaginal sclerite is irregular, with a ventrally directed process, arched lamina, and recurved distal end. The haptor presents unequal ventral and dorsal anchors with poorly developed roots; the ventral bar is straight and robust while the dorsal bar is slender with a small mid-region projection. Hook pairs I and V are morphologically distinct from the remaining pairs (II-IV and VI-VII), which share an erect thumb, slightly curved shank, and short filament. The discovery of two new species of Urocleidoides brings the number of valid species in the genus to 67 and constitutes the first parasitological record for C. spilurus; it also represents the first species of the genus described in a curimatid host from the Peruvian Amazon.