Fig. 12. Majella pristis n in Periclimenaeus djiboutensis Bruce 1970 Author Reyes, Jhoe Programa de Pós-graduação em Biologia de Ambientes Aquáticos Continentais (PPGBAC / FURG), Instituto de Ciências Biológicas, Universidade Federal do Rio Grande, RS, Brazil. * Correspondence: E-mail: rtvianna @ gmail. com (Vianna). & Universidade Federal do Rio Grande, Instituto de Ciências Biológicas, Laboratório de Biologia de Parasitos de Organismos Aquáticos, Av. rtvianna@gmail.com Author Binow, Daniela Universidade Federal do Rio Grande, Instituto de Ciências Biológicas, Laboratório de Biologia de Parasitos de Organismos Aquáticos, Av. Author Vianna, Rogério T. Programa de Pós-graduação em Biologia de Ambientes Aquáticos Continentais (PPGBAC / FURG), Instituto de Ciências Biológicas, Universidade Federal do Rio Grande, RS, Brazil. * Correspondence: E-mail: rtvianna @ gmail. com (Vianna). & Universidade Federal do Rio Grande, Instituto de Ciências Biológicas, Laboratório de Biologia de Parasitos de Organismos Aquáticos, Av. rtvianna@gmail.com Author Brusa, Francisco División Zoología Invertebrados, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Boulevard 120 & 61, La Plata, Argentina. E-mail: fbrusa @ fcnym. unlp. edu. ar (Brusa) & Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina fbrusa@fcnym.unlp.edu.ar Author Martins, Samantha E. Programa de Pós-graduação em Biologia de Ambientes Aquáticos Continentais (PPGBAC / FURG), Instituto de Ciências Biológicas, Universidade Federal do Rio Grande, RS, Brazil. * Correspondence: E-mail: rtvianna @ gmail. com (Vianna). & Norwegian Institute for Water Research (NIVA), Ecotoxicology and Risk Assessment Section, Gaustadalléen 21, 0349, Oslo, Norway. rtvianna@gmail.com text Zoological Studies 2021 2021-05-27 60 22 1 33 http://dx.doi.org/10.5281/zenodo.12823688 journal article 10.6620/ZS.2021.60-22 1810-522X PMC8598982 34853612 12824095 Gieysztoria evelinae ( Marcus, 1946 ) Luther, 1955 ( Fig. 7A–C ) Synonym: Microdalyellia evelinae Marcus, 1946 . Studied material : A single individual studied alive, afterwards whole mounted in Hoyer’s medium (MZUSP PL 2236). Localities : Sites 3 ( 18/02/2019 ), associated with phytal microhabitat. Description : The body is 0.9 mm long and 0.2 mm wide; anterior end bluntly rounded, caudal end pointed, tail-like shape; brownish-orange pigmentation concentrated especially behind the pharynx. Two black bean-like eyes located at the anterior region of the body. The pharynx is 137.2 μm long and 111.2 μm wide. Two dorsal feathery vitellaria (357.9 μm long) with finger-like prolongations ( Fig. 7A ). The male reproductive system comprised by two rear lateral testes, seminal vesicle (60.7 μm long, 95.4 μm wide), prostatic vesicle (60.4 μm long, 88.3 μm wide) and a penis stylet ( Fig. 7B ). The penis stylet is 72.9 µm in total length, with a dorsal opened girdle and distal spines. The girdle is composed by a proximal ring (24.77 μm in height and 47.61 μm in width) united by bridges (5.4 μm in height) to a distal ring ( Fig. 7C 1 ). The distal ring bears spines that are composed of two different groups. The first group is composed of four hollow well-developed spines (41.7 μm, n = 4, length) with a broad triangular slightly outward-curved base (18.4 μm, n = 1, width) ( Fig. 7C 1 , C 4 ). The second group bears five to seven thin fine spines (39.7 μm, n = 7, length) with its distal tip slightly curved outward, located interspersed with the first group of spines and are connected by its base to the distal ring ( Fig. 7C 1–2 ). The female reproductive system is composed of a saccular ovary (113.7 µm long), a seminal receptacle, uterus and a copulatory bursa. Male and female reproductive systems discharge into the common genital pore which is located at the posterior 1/3 of the body. Taxonomic remarks : The above-mentioned features follow descriptions given by Marcus (1946) and Brusa et al. (2008) . The body length (1700 µm) of the original description ( Marcus 1946 ) is bigger than specimens from the ESEC Taim. Our specimens are bigger than those found in Argentina (483–583 µm) ( Brusa et al. 2008 ). However, the total length of the stylet of our findings (72.9 µm) is smaller than those from Argentina (90–100 µm) ( Brusa et al. 2008 ) and São Paulo (90–100 µm) ( Marcus 1946 ). The same trait is observed when comparing the length of distal spines, which are 50-60 μm and 60 μm for Argentinian and Brazilian specimens, respectively ( Brusa et al. 2008 ; Marcus 1946 ). Although stylet dimensions are smaller than those previously described, the stylet configuration remains the same. Fig. 7. Live specimens of Gieysztoria . (A–C) Gieysztoria evelinae : (A) lateral view of a free-swimming individual, (B) detail of the posterior body region with details of the copulatory organs and (C1–4) detail of the penis stylet in different focal planes. (D–F) Gieysztoria hymanae : (D) dorsal view of a mature individual, (E) posterior body region with details of the copulatory organs and (F1–4) detail of the penis stylet in different focal planes. Distribution : The species was previously recorded from Brazil ( São Paulo , Corôa lagoon) ( Marcus 1946 ) and Argentina ( Buenos Aires province , littoral of the Río de la Plata: Atalaya and La Matilde stream) ( Brusa et al. 2008 ).