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A new species of Pseudione Kossmann, 1881 is described from two parasitized specimens of the clawed lobster Nephropsis aculeata Smith, 1881, collected from Brazilian waters in the southwestern Atlantic. It is the second species of the genus from Brazil and is the fourth species parasitizing nephropid lobsters in the world.

The anomuran family Porcellanidae Haworth, 1825 occurs worldwide in tropical and temperate marine habitats, especially in intertidal and subtidal zones (Ferreira & Melo, 2016;Osawa & McLaughlin, 2010). The family comprises around 30 genera and 280 species described (Bezerra et al., 2019). Most porcelain crab species are free-living and can be found on rocky shores, coral reefs and estuarine areas (Veloso, 1999). Some display symbiotic relationships with other organisms, both free-living such as shrimps, hermit crabs, turtles and fishes (

Bopyridae is the largest family of epicaridean isopods. There are currently eight subfamilies within Bopyridae, most of which live lodged in the branchial chamber or attached to the pleon of their definitive decapod hosts. Three of the eight subfamilies are exclusive parasites of caridean shrimps, Argeiinae, Bopyrinae and Hemiarthrinae. Bopyrinae is the second largest subfamily of Bopyridae, with 122 species and 27 genera described. They are found in the branchial chamber of their caridean hosts. Here, we describe two new species belonging to the genera Parabopyrella and Probopyriscus, parasitizing Alpheus packardii and Palaemon northropi respectively, from the southwestern Atlantic Ocean. The material examined is deposited in the Carcinological Collection of the Departamento de Zoologia, Universidade Federal do Rio Grande do Sul (UFRGS). Specimens were dissected and female pereiopods 1 and 7 were mounted on slides. Illustrations were made with the aid of a camara lucida fitted on a stereomicroscope and compound microscope. The parasite specimens were measured for total length (TL), i.e. from the anterior margin of the cephalon to the posterior margin of the pleotelson, and the hosts for carapace length (CL), i.e. from the tip of rostrum to the mid-dorsal posterior margin of carapace. The female of Parabopyrella sp. nov. (TL = 3.8 mm) is morphologically similar to P. lata, but differs in having maxilliped with an articulated palp with ten setae and a more acute spur; barbula with two lateral projections on each side, inner ones curved outwards. The dwarf male was not found. The new species represents the second record of the genus from Brazilian waters. Probopyriscus sp. nov. is morphologically similar to the congeners, but the female specimens differ in having the head inserted into the first pereomere, maxilliped palp with nine setae and more acute spur and the oostegite 1 with posterior lobe longer with inner margin concave. In addition, the male specimens show the pleon proportionally longer and the lateral margins of the first to five pleomeres only weekly curved posteriorly. The females' size ranged from 1.2 to 4.4 mm, and males from 0.9 to 1.1 mm. The new species represents the second species of the genus Probopyriscus and the first record from the Atlantic Ocean.

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