The Amazon Basin occupies a vast portion of northern South America and contains some of the highest species richness in the world. The northern Brazilian state of Amapá is delimited by the Amazonas River to the south, the Oyapock River to the northern boundary with French Guyana, and the Atlantic northeastern coast to Amazon estuary. Despite several expeditions to the Amazon in recent decades, little is known about the freshwater ichthyofauna from Amapá, with records limited to local inventories and species descriptions. This paper presents a compilation of the freshwater fish diversity sampled in fifteen sites covering two major Amapá ecoregions during the dry season of 2015. 120 species representing eight orders and 40 families are reported upon in this work. Eight species appear for the first time in the Brazilian territory providing new information for future conservation status evaluations.

This study described the occurrence of Argulus juparanensis Lemos de Castro, 1950 (Argulidae) in tegument of Potamotrygon constellata, Potamotrygon dumerilii, Potamotrygon motoro, Potamotrygon orbignyi, Potamotrygon scobina and Potamotrygon from mouth of the Amazon River, Northern Brazil. Out of 103 Potamotrygon spp. specimens examined, 88.3% (n= 91) were infested by A. juparanensis. This is the first reports of A. juparanensis for the stingrays on the mouth of Amazon River.

A new species of Myloplus Gill is described from Eastern Tumucumaque Mountain Range, drainages of the Oyapock and Araguari rivers between Brazil and French Guiana. The new species is diagnosed by having comparatively large scales on the flanks, resulting in lower counts when compared with congeners, i.e., 59 to 70 total perforated scales on lateral line, 31 to 35 longitudinal scales above lateral line, 24 to 29 longitudinal scales below lateral line, and 22 to 26 circumpeduncular scale rows. The new species most closely resembles Myloplus rubripinnis by sharing with this species a general rounded shape, a similar color pattern, and a high number of rays, i.e., 23 to 25 branched dorsal-fin rays and 35 to 38 branched anal-fin rays in the new species (vs. 24 to 25 and 32 to 40, respectively, in M. rubripinnis). After reviewing the available type-specimens of all Myloplus species, M. rubripinnis is re-diagnosed as having higher counts of branched dorsal-fin rays and anal-fin rays combined to tiny scales on flanks, i.e., 85 to 89 total perforated scales on lateral line, 38 to 45 longitudinal scales above lateral line, 33 to 42 longitudinal scales below lateral line, and 30 to 39 circumpeduncular scale rows.

O número de nematódeos descritos em elasmobrânquios é relativamente pequeno, sendo encontrados majoritariamente no trato digestório. Apesar de alguns relatos descritos, a literatura a respeito ainda é considerada escassa principalmente sobre a associação parasita-hospedeiro. Diante disso, o objetivo deste trabalho foi avaliar os índices parasitários de larvas Brevimulticaecum sp. na válvula espiral de Potamotrygon motoro provenientes do arquipélago do Bailique, em Macapá no estado do Amapá, Brasil. Registrou-se em 20,41% das raias coletadas a presença de larvas de Brevimulticaecum sp., sendo a intensidade média de 20,10 larvas/peixe e a abundância média de 4,10. São poucos os registros deste parasito em peixes no Brasil, sendo que já foi relatada sua ocorrência no estômago de P. motoro e Potamotrygon falkneri. As diferenças entre os parâmetros parasitários podem ser um indicador de alimentação e/ou diferenças comportamentais entre os sexos. Este é o primeiro estudo sobre nematóides de potamotrigonídeos na região Norte, ampliando o conhecimento da biodiversidade desta região.   Palavras-chave: Helmintos. Nematoda; Elasmobrânquio. Válvula Espiral.   Abstract The number of nematodes described in elasmobranchs is relatively small, being found mostly in the digestive tract. Despite some reports described, the literature on this subject is still considered scarce, mainly on the parasite-host association. Therefore, the objective of this work was to evaluate the parasitic indices of Brevimulticaecum sp. the Potamotrygon motoro spiral valve from the Bailique archipelago, in Macapá in the state of Amapá, Brazil. Larvae of Brevimulticaecum sp. Were recorded in 20.41% of the rays collected, with an average intensity of 20.10 larvae / fish and an average abundance of 4.10. There are few records of this parasite in fish in Brazil, and its occurrence in the stomach of P. motoro and Potamotrygon falkneri has been reported. Differences between parasitic parameters can be an indicator of diet and / or behavioral differences between genders. This is the first study on potamotrigonid nematodes in the North, expanding knowledge of this region's biodiversity.   Keywords: Helminths. Nematoda. Elasmobranchs. Spiral Valve.