Abstract During a search for parasites in fishes from Iguazu River, Argentina, a nymph of pentastomid was found encysted on mesenteries of Phalloceros harpagos. The 28S rDNA and COI mt-DNA were used to compare with the sequences deposited in the GenBank. Pentastomid nymphs belong to the subfamily Diesingiinae (Sebekidae) for having chloride cell pores distributed in a single row per annulus; also, the hooks and rows of spines of our material differ to other genera. Present specimens are most likely Diesingia sp., having 63-74 annuli, a U shaped oral cadre with fibers closing anteriorly and a peg like extension of the oral cadre. The 28S rDNA analysis places our samples into a sister group of Alofia sp., but the COI mt-DNA situate them on the base of the clade. In conclusion, our pentastomid positively belongs to Diesingia sp., however, indisputable assignation requires a reliable description of the nymph, or the availability of sequences linking nymphs and adults, which even could provide evidence of a new hitherto undescribed genus. Aditionally, the systematic position of Sebekia oxycephala previously described by P. harpagos is discussed on the basis of our results, allowing us to suggest a re-assignation of such specimens to the genus Diesingia.

Abstract The new genus Maxiclavella is proposed to accommodate Clavella simplex Castro Romero and Baeza Kuroki, 1985, which differs from Clavella species, including long and narrow cephalothorax, small bulla, and simple armature of the antenna and antennule. Praeclavella nasalis, new genus and species, was found parasitizing the olfactory sacs of Isacia conceptionis. Praeclavella nasalis could be differentiated from other Clavella species by a biramous antenna with an exopod shorter than the endopod, the base of the cephalothorax with a large lobular and suborbicular projection on each side, a suborbicular bulla, mandibles without secondary teeth, and a suboval male body type. Males of both genera fit well in the Clavella-clade male type, although they differ from each other in many aspects, mainly in the position of the buccal area, which is oriented ventrally in Maxiclavella and distally in Praeclavella nasalis, and in a genital process, which is present in the latter and absent in the former. Genetic distances of mtDNA COI and 28S rDNA supported the validity of the two new genera parasitizing the same host, I. conceptionis. Also Clavella-branch (Clavellinae Wilson), a key based genera on female specimens is presented.

In March 2020, in the context of the pandemic produced by the covid-19 outbreak that also affected higher education, using the Information and Communication Technologies (ICT) to resolve the situation. The impact, which caused the adjustment to virtuality, had obstacles and difficulties, as well as challenges and new competences, for teachers and students. In this work, the responses of first-year students of annual course, of the Faculty of Natural Sciences and Museum-UNLP, to the survey carried out at the end of the course, are analyzed. This analysis allows us to know the perceptions they had during the course in virtual mode, since, being the first time of this experience, it is important to know the opinions that allow us to improve teaching practices. This new form of teaching put into practice due to the particular health situation opens up a range of possibilities, including the possible implementation of a bimodal course.

A partir del mes de Marzo de 2020, en el contexto de la pandemia producida por el brote de covid-19 que afectó también a la educación superior, recurriendo al uso de las TecnologÃas de la Información y la comunicación (TIC) para afrontar la situación. El impacto, que provocó el ajuste a lo virtual, contó con obstáculos y dificultades, asà como, retos y nuevas competencias, para docentes y alumnos. En este trabajo se analizan las respuestas de les alumnos de primer año de una asignatura anual de la Facultad de Ciencias Naturales y Museo- UNLP, a la encuesta realizada al finalizar la cursada. Este análisis nos permite conocer las percepciones que tuvieron durante el desarrollo de la materia en modo virtual, ya que, al ser la primera vez de esta experiencia, es importante conocer las opiniones que nos permitan mejorar las prácticas docentes. Esta nueva forma de enseñanza puesta en práctica debido a la situación sanitaria particular, nos abre un abanico de posibilidades, incluyendo la posible implementación de una cursada bimodal.

Abstract: Riggia puyensis, an ectoparasitic isopod, was collected in juvenile Chaetostoma breve and Chaetostoma microps host specimens from the Amazonian region of Ecuador. The aim of this work is to study the possible injury that the parasite causes in its host. R. puyensis was found covered by a fold of the skin, which formed a sort of pocket or pouch within the host’s peritoneal cavity. The alterations described in the epidermis were associated with the mechanical action of the isopod inside the pouch.

In total 374 specimens corresponding to four species of shrimp: Artemesia longinaris, Pleoticus muelleri, Peisos petrunkevitchii, Palaemon macrodactylus, and two species of crabs: Neohelice granulata and Cyrtograpsus angulatus were studied in the search of white spot syndrome virus (WSSV). The crustaceans were collected in the estuary of Bahia Blanca, the port of Mar del Plata and the Samborombón Bay, Argentina, between 2010 and 2014. A polymerase chain reaction (PCR) analysis in all of them has not detected any virus presence. These new results suggest that the discovery of infected shrimp in 2008-09 in the Bahia Blanca estuary may have been a one-time local event, promoted by special conditions of seawater temperature inside the estuary, coincident with the presence of a virus carrier or transporter. To determine if the virus was finally installed in the estuary of Bahia Blanca more screening are needed coming from a larger number of shrimp samples. These studies will be necessary mainly in A. longinaris (Penaeidae) since this family of shrimps is most susceptible to be affected by WSSV.

ABSTRACT Myxosporean Myxobolus saladensis sp. nov. in the gills of Mugil liza Valenciennes, 1836 from Samborombón Bay was described by light and electron microscopy studies. Spores were pyriform and binucleated, measuring 10.63±0.36 µm (n=20) long, 9.24±0.50 µm (n=20) wide and 4.13±0.36 µm (n=20) thick, included in polysporic cyst-like plasmodia. Elongated pyriform polar capsules were of equal size (3.84±0.27 µm long and 2.30±0.12 µm wide). The sporoplasm contained some sporoplasmosomes. Each PC contained a polar filament with 4-5 coils obliquely arranged in relation to the polar capsules axis. The PC wall was composed of two layers of different electron densities. Based on the morphological and ultrastructure differences of the spore to those of previously described species of Myxobolus, we describe a new species, Myxobolus saladensis sp. nov.

ABSTRACT Jenynsia multidentata Jenyns, 1842 (one-sided livebearers) are euryhaline viviparous fish of small size, used in the laboratory experiment, important as resource for biological control of mosquito’s larva and a key species to recover eutrophic lakes. Works have been published dealing with parasite biodiversity of this host, but little has been studied about the parasite community ecology. From early 2009 to ends of 2010 specimens of J. multidentata were collected from two places, the Salado Relief Channel (S.R.C.) on Samborombón Bay and the Sauce Chico River near to the city of Bahia Blanca (B.B.). All fish were sexed, measured and grouped into sizes/age classes. The fishes from both sites harbored 16 parasitic species: nine digenean, one monogenean, one metacestode, one acanthocephalan, two nematode and two copepods. Lecithaster confusus Odhner, 1905, the metacercariae Hemiuridae gen. sp. indet., metacercariae Thylodelphys sp. (inside the eye), Glossocercus sp. nematode L4 (intestine) and Ergasilus sieboldii Nordmann, 1832 are new records for the host. The high number of larval stages made of this fish a link between micro and macroecosystems. The size 2 had the higher biodiversity in both sites, which could be the most suitable age to store the maximal number of parasite of the environment and have a more equitability in their distribution on the host. In B.B. some parasites had higher prevalence and mean abun dance due to the small size of the waterbody compared with the S.R.C. Despite that, in S.R.C. exist a higher specific richness and biodiversity due the daily flow of saline and freshwater and proximity of the sample site to the mouth of the channel in the bay. This is the first approximation to an analysis of the parasitic ecology on this host.

RESUMEN Jenynsia multidentata Jenyns, 1842 (madrecitas) son peces viviparous, eurihalinos de pequeño tamaño usados en experimientos de laboratorio, como un recurso importante para el control biológico de larvas de mosquito y una especie clave para recuperar lagos eutrofizados. Han sido publicados varios trabajos acerca de la biodiversidad parasitaria de este pez pero poco es conocido acerca de la ecologia de la comunidad parasitaria de este hospedador. pero poco se conoce acerca de su ecología parasitaria. Durante los meses de primavera y verano en el 2009 y 2010, especímenes de J. multidentata se colectaron del Canal Colector del Salado (S.R.C.) en la Bahía de Samborombón y del Rio Sauce Chico cercano a la ciudad de Bahía Blanca (B.B.), fueron sexados, medidos y agrupados en clases según su tamaño/edad. Los peces de los dos sitios albergaron 16 especies de parásitos: nueve digeneos, un monogeneo, un cestodo, un acantocéfalo, dos nematodos y dos copépodos. Lecithaster confusus Odhner, 1905, la metacercaria Hemiuridae gen. sp. indet., metacercaria Thylodelphys sp. (en el ojo), Glossocercus sp. nematode L4 (intestino) y de Ergasilus sieboldii Nordmann, 1832 son nuevas citas para el hospedador. El gran número de estadios larvales hacen de este pez un nexo entre micro y macroecosistemas. La talla 2 tuvo una mayor biodiversidad en ambos sitios, la cual puede ser la edad más apropiada para recolectar el máximo número de parásitos del ambiente y tener una distribución dentro del hospedador de mayor equitabilidad. En B.B. algunos parasitos tuvieron mayor prevalencia y abundancia media debido al menor tamaño del cuerpo de agua comparado con S.R.C. A pesar de esto, en S.R.C. existe una mayor riqueza específica y biodiversidad debido al flujo diario de agua dulce y salina y a la proximidad del sitio de muestreo a la desembocadura del canal en la Bahía. El gran número de parásitos en los machos puede deberse a un cambio en el uso de la energía que se focaliza en la reproducción. Esta es la primera aproximación a un análisis de la ecología parasitaria de este hospedador y, como resultado, podemos ver algún tipo de influencia del mismo que no debe ser ignorado y debería ser estudiado en el futuro considerando cada parasito como la interrelación entre ellos y el hospedador.

ABSTRACT Since temperature is a key condition in the initiation of cercarial emergence, the objective of the work reported here was to evaluate the effect of that variable on the shedding of two morphologic and taxonomic types of cercariae. Bioassays were accordingly performed with snails naturally infected with either monostome or pleurolophocercous cercariae because those two cercarial types were found to be the most prevalent in the environment under study. The snails were placed in 6-ml circular plastic dishes with soft plastic stoppers containing 3 ml of reconstituted water and then sequentially exposed for 24 h to a 14:10-h light:dark cycle at 20, 25, or 30 °C. The data were analyzed at a significance level of p <0.05 by means of the InfoStat program. The optimum temperature for cercarial emergence was typically in the range of 25 °C and decreased significantly at 30 °C. We observed no significant difference in the number of cercariae emerging between the two morphologic types.

RESUMEN Considerando que la temperatura es un factor clave en la emergencia de cercarias, el objetivo de este trabajo fue evaluar el efecto de ésta variable sobre la emergencia de dos tipos morfológicos de cercarias. Los bioensayos se realizaron con caracoles naturalmente infectados con cercarias de los tipos monostoma o pleurolofocerca, debido a que estos dos tipos fueron los más prevalentes en el ambiente en estudio. Los caracoles fueron ubicados en cápsulas plásticas de 6 ml conteniendo 3 ml de agua reconstituida, y entonces fueron secuencialmente expuestos por 24 h con un ciclo 14:10 h luz:oscuridad a 20, 25 y 30 °C. Los datos fueron analizados a un nivel de significación de p<0.05 con el programa InfoStat. Los resultados mostraron que la temperatura óptima de la emergencia de cercarias estuvo en el rango de 25 °C, y disminuyó significativamente a 30 °C. Se observó también que no existía diferencia significativa en el número de cercarias emergentes entre los dos tipos morfológicos.

ABSTRACT Mugil liza Valenciennes, 1836 is an economically important food fish and has been recommended for aquaculture in South America. A total of 278 fishes were collected in the spring and summer of 2009 and 2010. These fish were sorted into sample groups according to their size class. We used Bayesian statistics and 95% credible intervals for each parameter tested were calculated. Fish studied harbored a total of 15 different species of parasites. Diversity of parasite species found on Mugil liza was greatest at the S.R.C. collection site, but evidenced a lower species richness than at A.R. site. The 1st size fishes of both sites evidenced greater parasite diversity than either 2nd or 3rd size fish. Differences observed could be explained by the different use of habitat types at the two sites or differential susceptibility to infection by parasites. The dominance of D. fastigatainfluenced observed results of lower community diversity indexes. New works elucidating different parasite life cycles within juvenile and adults ofM. liza in Argentina, promise to be important for determining the risk of the parasitism by zoonotic metacercariae A. (P.) longa and use of this fish as food and an economic resource, and the possible use of mullet parasites in other promising fields as indicators of biodiversity, and/ or water contamination.

RESUMEN Mugil liza, Valenciennes, 1836 es un pez de importancia comercial y ha sido recomendado en Sudamerica para la acuicultura. Los peces se distribuyeron en grupos de acuerdo con la talla. Usamos estadística Bayesiana e intervalos de credibilidad del 95% para cada parámetro calculado. Los peces alojaron un total de 15 especies parasitarias. La diversidad de las especies parasitas de M. liza fue mayor en el sitio de colecta S.R.C., pero evidencio una menor riqueza especifica que en A.R. La 1er talla de los peces de ambos sitios evidencio una mayor diversidad parasitaria que la 2da o 3er talla. Las diferencias observadas se pueden explicar por un uso diferente del hábitat en los dos sitios o a una susceptibilidad diferente a la infección por los parasitos. La influencia de la dominancia de D. fastigata resulta en el menor índice de diversidad de la comunidad. Nuevos trabajos que diluciden los diferentes ciclos de vida de los parásitos en los juveniles y adultos de M. liza en Argentina, prometen ser importantes para determinar el riesgo del parasitismo de la metacercaria zoonotica A. (P.) longa y el uso de este pez como alimento, una fuente económica y el posible uso de los parásitos de la lisa en otros promisorios campos como indicadores de biodiversidad y/o contaminación acuática.

Exemplares de metacercárias do gênero Opechona (Trematoda: Digenea: Lepocreadiidae) são descritos parasitando "celenterados" (cifomedusas e ctenóforos) no sudeste do Brasil (estado de São Paulo). Os vermes foram comparados a outras espécies de Opechona ocorrentes no litoral brasileiro, porém nenhuma associação foi realizada devido às demais espécies terem sido descritas a partir de exemplares adultos. São apresentadas suposições sobre as possíveis formas de transferência dos parasitas.

Metacercaria specimens of the genus Opechona (Trematoda: Digenea: Lepocreadiidae) are described parasitizing "coelenterates" (scyphomedusae and ctenophores) from Southeastern Brazil (São Paulo state). The worms are compared to other Opechona species occurring on the Brazilian coast, but no association has been made because only adult forms of these species have been described. Suppositions as to the possible transference of the parasites are made.

Opecoeloides feliciae n. sp., first record of opecoelid metacercariae in commercial shrimps of South Atlantic Ocean, parasitizing Cynoscion striatus (adults) and Artemesia longinaris (metacercariae), is described, illustrated and compared with related species of the genus. Adults, immature worms and metacercariae are compared, and rates of prevalence and intensity of infection are also given.

Based on a study of the larvae from two helminth species parasitizing the crab Cyrtograpsus angulatus Dana, 1851 (Microphallus szidati Martorelli, 1986 and Falsifilicollis chasmagnathi Holcman-Spector et al., 1977), from Mar chiquita lagoom (Argentina) together with the analyses of their life cycles and rates of prevalence, intensity and association coefficient (compared in definitive and intermediate host) the following conclusions have been reached: a) C. angulatus suns to be an excelent intermediate host in the life-cycles of the studied helminths; b) the size of the crabs and the occurence of natural amputations in the females (Spivak & Politis, in press) appeared correlated with prevalence; c) in the studied crabs the pervalence fo F. chasmagnathi is higher in males than in females; d) the intensity did not appear correlated with size and sex of the intermediate host; e) M. szidati and F. chasmagnathi are closely associated with the intermediate host; f) C. angulatus and Himantopus melanurus Vieillot, 1817 (Aves; Recurvirostridae) are reported as new intermediate and definitive hosts, respectively, for F. chasmagnathi; g) Chasmagnathus granulata Dana, 1851 (Cruscea; Brachyura) is reported as new intermediate host for M. szidati.

Basándose en el estudio de los helmintos larvales parásitos del cangrejo Cyrtograpsus angulatus Dana, 1851 (Microphallus szidati Martorelli, 1986 (Digenea; Microphallidae) y Falsifilicollis chasmagnathi Holcman-Spector et al., 1977 (Acathocephala; Fillicollidae) conjuntamente con el análisis de sus ciclos biológicos y el estudio de la prevalencia, intensidad y de los índices de asociación (comparados entre los hospedadores intermediarios y definitivos) se pudo concluir que: a) C. angulatus parece ser un excelente hospedador intermediario en los ciclos de vida de los helmintos estudiados; b) el tamaño de los cangrejos y la ocurrencia de amputaciones naturales en las hembras de mayor tamaño Spivak & Politis (en prensa) aparecen correlacionadas con la prevalencia; c) en los cangrejos estudiados la prevalencia para F. chasmagnathi fue mayor en los machos que en las hembras; d) la intensidad no apareció correlacionada con el tamño y el sexo de los hospedadores intermediarios; e) M. szidati y F. chasmagnathi estan fuertemente asociados en el hospedador intermediario; f) C. angulatus e Himantopus melanurus Vieilot, 1817 (Aves; Recurvirostridae) son citados como nuevos hospedadores, intermediario y denitivo respectivamente, para F. chasmagnathi; g) Chasmagnathus granulata Dana, 1851 es citado como un nuevo hospedador intermediario para M. szidati.