Despite the ubiquity of Cucullanus spp. in aquatic ecosystems around the world, their embryonic and post-embryonic development, as well as transmission patterns, remain little known and in some cases controversial. In the present study, comparative and embryological data of Cucullanus pinnai pinnai (Travassos, Artigas & Pereira, 1928) are provided. Adults from Rhamdia quelen (Quoy & Gaimard, 1824) (Heptapteridae) are described and illustrated by scanning electron microphotography. Eggs were obtained from gravid females and embryonic and larval development was followed in vitro. The L and L 2 3 stages are described and illustrated for the first time. The embryonic development of C. pinnai pinnai goes very fast at 20-22ºC. In five days, hatching takes place and the free L remain alive for less than two weeks. 2 A heteroxenic pattern of transmission is hypothesized involving R. quelen as definitive host and Bryconamericus iheringii (Boulenger, 1887) (Characidae) as the intermediate host. ISSN Versión impresa 2218-6425 ISSN Versión Electrónica 1995-1043 Neotropical Helminthology, 2020, 14(2), jul-dic:217-225. ORIGINAL ARTICLE / ARTÍCULO ORIGINAL ON THE LIFE CYCLE OF CUCULLANUS PINNAI PINNAI (TRAVASSOS, ARTIGAS & PEREIRA, 1928) (NEMATODA: CUCULLANIDAE) PARASITE OF RHAMDIA QUELEN (QUOY & GAIMARD, 1824) (SILURIFORMES) FROM ITS SOUTHERN LOCALITIES ACERCA DEL CICLO DE VIDA DE CUCULLANUS PINNAI PINNAI (TRAVASSOS, ARTIGAS & PEREIRA, 1928) (NEMATODA: CUCULLANIDAE) PARÁSITO DE RHAMDIA QUELEN (QUOY & GAIMARD, 1824) (SILURIFORMES) EN SU DISTRIBUCIÓN MÁS MERIDIONAL 1 Universidad Nacional del Sur, Departamento de Biología, Bioquímica y Farmacia, calle San Juan nº 670 (8000) Bahía Blanca, Buenos Aires, Argentina. 2 Instituto de Ciencias Biológicas y Biomédicas del Sur (INBIOSUR/CONICET) calle San Juan n°671 (8000) Bahía Blanca, Buenos Aires, Argentina *Corresponding author: rtanzola@uns.edu.ar 1,2,* 1,2 1 1 Ruben Daniel Tanzola ; Silvia Elizabeth Guagliardo ; Cintia Poggi ; Bárbara Angeletti & Carla Belén 1,2 Schwerdt Neotropical Helminthology 217 doi:10.24039/rnh2020142808 ÓrganooficialdelaAsociaciónPeruanadeHelmintologíaeInvertebradosAfines(APHIA) Lima-Perú Volume14,Number2(jul-dec)2020 ABSTRACT Keywords: Cucullanus pinnai – freshwater fishes – life cycle – Nematoda – Rhamdia quelen