A new species of Pseudione sensu lato (Isopoda: Bopyridae) on a squat lobster host from the deep South-West Atlantic.

A new bopyrid, Pseudione chiesai n. sp., is herein described based on an ovigerous female and an adult male found in the right branchial chamber on a specimen of Munida spinosa Henderson, 1885. This parasite was collected in the Mar del Plata submarine canyon at 819 m depth during the expedition Talud Continental I carried out by the Argentine RV Puerto Deseado in 2012. P. chiesai n. sp. belongs to the Pseudione crels group sensu Bourdon (1972, 1976), which currently contains seven species, all of which have galatheoid crabs as hosts. P. chiesai n. sp. can be separated from the other species in the Pseudione crels group by the following combination of characters: (1) both sides of the body convex, (2) frontal lamina with a few, shallow indentations, (3) coxal plates 14 and tergal projections 14 with distinct irregular margins, mainly on the right side, (4) pereomeres 57 with single/branched lateral digitations, (5) maxilliped palp well-developed and setose, and (6) pleon with lateral plates 15 distally rounded and directed laterally. The taxonomic position of this new species is briefly discussed.

Acutihumerus patagoniensis (Sieg, 1986) (Tanaidacea: Kalliapseudidae): supplementary description and remarks on its taxonomic status.

Acutihumerus patagoniensis (Sieg, 1986) was originally described based on a single specimen from Golfo Nuevo, northern Patagonia, Argentina. Over 3000 specimens referable to this species from just a few miles of its type locality are now available. Based on these specimens, the description of A. patagoniensis is completed and the ontogenetic changes of the male cheliped are described and illustrated. Acutihumerus patagoniensis has recently been considered a junior synonym of A. cavooreni (Bacescu & Absalao, 1985) from southern Brazil. However, these species can be distinguished mainly by the male chela: A. patagoniensis has a much wider notch palm than A. cavooreni. Furthermore, most of the males herein reported from off the Río de la Plata have a chela with a narrow notch, a fact that suggests that this area might be a zone of hybridization or contact between A. patagoniensis and A. cavooreni. Hence, we claim that the recently proposed synonymy has not been proven, and the resolution of this taxonomic problem must await additional specimens of A. cavooreni from its type locality (Rio Grande do Sul, Brazil). 

Remarks on the deep-sea genus Chalarostylis (Cumacea: Lampropidae).

Chalarostylis is a deep-sea genus close to Hemilamprops but easily distinguished from the latter mainly by its robust first pereopod. However, this appendage is frequently broken off at the anterior margin of the basis, making the identification of the species of the genus difficult. Regarding Hemilamprops brenkei, both the adult male holotype and the additional specimens herein reported from the Weddell Sea and the Guinea, Argentine and Brazilian Basins exhibit a huge first pereopod. Thus, this species is transferred to Chalarostylis and its description completed. Two other species until now in Hemilamprops, H. canadensis and H. longisetae are also transferred to Chalarostylis. In addition, an unknown species of Chalarostylis from the Bay of Biscay for which no name is given is briefly described. The diagnosis of this genus is emended. 

On two South-West Atlantic Diastylis (Cumacea: Crustacea), D. obliquisulcata n: sp. and D. geocostae, with remarks on this speciose genus.

A new species, Diastylis obliquisulcata from eastern Patagonia, is fully described and illustrated based on specimens collected in shallow waters. Diastylis obliquisulcata shares with 14 other species of this genus an opercular maxilliped 3, a short telson and rudimentary exopods on pereopods 3 and 4 in the females. Diastylis obliquisulcata can be easily distinguished from all these species by the females having an oblique groove or sulcus on each side of the carapace. The taxonomic position of this group of species in the genus Diastylis is discussed. The adult male of Diastylis geocostae is described for the first time, the adult female briefly redescribed, and its distribution, up to now known from the type locality only (Cabo Frio, Rio de Janeiro State), is extended to off Rawson, Argentina. Within this species there are reported ontogenetic changes in the carapace ornamentation, in the chaetotaxy of the telson, and in the length ratio between the telson and the uropod peduncle.

Two new species of the genus Munnogonium (Isopoda: Asellota: Paramunnidae) from Argentina.

Two new species of paramunnid isopods from Argentina are described: Munnogonium quequensis n. sp. from Buenos Aires Province (Quequén) and M. diplonychia n. sp. from Patagonia (Comodoro Rivadavia, Rada Tilly and Puerto Deseado). Both species are distinguished from their congeners by having a tight tuft of setae on the frontal margin. These setae have been discovered after examining the specimens under scanning electron microscope; under dissecting microscope they look like a short blunt median projection. M. diplonychia n. sp. differs from M. quequensis n. sp. by having bifid claws on pereopods II-IV. Eighty of the 92 specimens of M. quequensis n. sp. examined were found attached to the sea star Astropecten brasiliensis, a fact that suggests an association between these two species.

Hyperparasitism of the cryptoniscid isopod Liriopsis pygmaea on the lithodid Paralomis granulosa from the Beagle Channel, Argentina.

A total of 29,570 false king crab Paralomis granulosa were sampled from the Beagle Channel (54 degrees 51'S, 68 degrees 12'W), Tierra del Fuego, Argentina, between July 1996 and August 1998. Crab size varied from 6.8 to 111.2 mm carapace length (CL). A few crabs parasitized by the rhizocephalan Briarosaccus callosus were found; prevalences of externae (the rhizocephalan reproductive body) and scars (the mark left on the host after the death of the parasite) were 0.28 and 0.16%, respectively. Of 85 externae examined, 55 were non-ovigerous and 30 ovigerous. The cryptoniscid isopod Liriopsis pygmaea infested 36.5% of the B. callosus examined. The most abundant stage was the cryptonicus larva, accounting for 208 of the 238 L. pygmaea recovered. Cryptonisci showed a highly aggregated distribution. A total of 92.7% of cryptonicsci were recovered inside empty externae, suggesting that the latter were attractive to cryptonisci. Early subadult females of L. pygmaea were rare; only 3 individuals occurred inside 1 ovigerous externa. Eight late subadult and 18 adult females were found on 3 and 7 non-ovigerous externae, respectively; in addition, 1 aberrant late subadult was found on 1 ovigerous externa. In the Beagle Channel, the population of P. granulosa harbours 3 different parasites: the bopyrid isopod Pseudione tuberculata, which reaches highest prevalence at 10 to 20 mm CL, the rhizocephalan B. callosus, with highest prevalence at 20 to 40 mm CL, and the cryptoniscid isopod L. pygmaea, which mainly infests rhizocephalan on crabs >40 mm CL.