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An updated taxonomic review of Malacostraca from the Neotropical regions is presented in this chapter. Dichotomous identification keys to the lowest justifiable taxonomic level based on the most recent literature are provided. Material preparation methods, defined morphological terms, and current limitations in the knowledge of the group are also presented. Additional information on the “Ecology and General Biology” can be found in Volume I of this book series (Thorp and Rogers, 2015, Elsevier).

Aim To understand the ecological and historical/evolutionary processes underlying an inverse latitudinal gradient of richness (LGR) using crustacean peracarid species as a model group. Location The Pacific coast of South America, along the Chilean coast between 18° S and 56° S. Methods The LGR was evaluated using a dataset including 320 marine peracarid species reported for the coasts of Chile. Five ecological hypotheses invoking a relationship between species richness and present-day conditions were tested: species–energy, species–area, Rapoport rescue effect, mid-domain geometric constraint and niche breadth. Historical/evolutionary hypotheses (i.e. biogeographic conservatism, and diversification rates) were indirectly tested by analysing the latitudinal variation in the taxonomic distinctness, the taxonomic conservatism of the midpoint of the latitudinal range and the degree of nestedness at different taxonomic levels. Results Richness increased poleward, varying approximately eightfold, following an inverse LGR coupled with an increase in bathymetric distribution. Overall this inverse LGR seems robust to uncertainties in the completeness of the species inventory. We found support for only two of the five ecological hypotheses tested: species–area and Rapoport rescue effect. Historical/evolutionary hypotheses seemed important in structuring the richness pattern, as indicated by the higher taxonomic distinctness in the southern region, the strong taxonomic inertia in the mean range size and the high degree of nestedness of assemblages at different taxonomic levels. Conclusions When combined, these results underscore the importance of longterm processes and historical/evolutionary explanations for the inverse LGR, conceptualized in what we term the ‘out of the deep south’ hypothesis that involves the effects of both biogeographic niche conservatism and evolutionary rates. We propose that the southern region may be a source of evolutionary novelties and/or exhibit higher diversification rates (i.e. higher speciation/lower extinction rates). Furthermore, phylogenetic conservatism of latitudinal range may limit the geographic expansion of these new taxa towards the depauperated northern region.

The freshwater amphipod genus Hyalella in Brazil has the second highest diversity in South America; it is only surpassed by the diversity found in the Andean Lake Titicaca. Ten species of Hyalella are known for Brazil: H. gracilicornis (Faxon, 1876); H. longistila (Faxon, 1876); H. warmingi Stebbing, 1899; H. meinerti Stebbing, 1899; H. curvispina Shoemaker, 1942; H. brasiliensis Bousfield, 1996; H. caeca Pereira, 1989; H. montenegrinae Bond-Buckup and Araujo, 1998; H. pseudoazteca Gonzalez and Watling, 2003; and H. dielaii Pereira, 2004. Two new species are described here, H. castroi and H. pleoacuta, both occurring in freshwater bodies of southern Brazil over 1.200 m high in the region of Aparados da Serra. A key for the species of Hyalella from Brazil is presented.

The description of the new species Hyalella pseudoazteca and redescriptions of H. gracilicornis (Faxon, 1876), H. longistila (Faxon, 1876) and H. warmingi Stebbing, 1899, are included in this work. The latter species are closely related by having sternal gills on segments 2-7, and are morphologically distinct from other hyalellid species known from the area. Hyalella pseudoazteca has a morphology similar to H. azteca (Saussure, 1858). However, H. pseudoazteca has dorsal flanges instead of carinae on peraeon 7 and pleon 1 and 2, two distal setae on the inner plate of maxilla 1, and one pappose seta on the inner margin of maxilla 2 inner plate. For comparisons with H. azteca see Gonzalez and Watling (2002).

The amphipod genus Hyalella has its highest diversity in the Andean Lake Titicaca. This genus is the only epigean amphipod present in South America. Eleven endemic and one non-endemic species are known from Lake Titicaca. An additional endemic species, Hyalella nefrens n. sp. and one non-endemic species Hyalella tiwanaku n. sp. are described here. Hyalella cuprea (Faxon, 1876), Hyalella latimanus (Faxon, 1876), Hyalella montforti Chevreux, 1907, and Hyalella neveulemairei Chevreux, 1904 are redescribed. The high diversity of Hyalella in the lake is not well understood, and it has been compared with the spectacular diversity of Lake Baikal.

Hyalella azteca is a species complex distributed in North, Central, and northern South America. The identity of the species has always been a problem, especially because the original description by Saussure (1858) from a “cistern” in Vera Cruz, Mexico, is poor, and the figures are not clear. Since then, mention of the type material or specimens from the type locality has not been made by investigators using the name H. azteca. Ecological and genetic information available today suggests that there are several species in the complex commonly referred to as H. azteca. The subtle morphological differences among the populations have made the problem of defining these species very complicated. To aid in this process, we present here the morphological description of H. azteca based on the syntype series established by Saussure and deposited in the Museum d'Histoire Naturelle, Ville de Geneve, Switzerland.

Hyalella is the only epigean freshwater amphipod present in Chile . H. chiloensis, H. costera and H. kochi are here described and illustrated. H. kochi is distributed in highland areas of the Andes in northern Chile; it is characterized by a short ramus on uropod 3 and a hammer-shaped gnathopod 1. H. costera and H. chiloensis are present in lowland areas, the latter restricted to the southern part of the country. These two species have a long ramus on uropod 3, but they differ in the shape and length of the palp on maxilla 1, the setation of peraeopods 3, 4, and telson. The presence in Chile of H. fossamancinii Cavalieri, 1959 is also reported here.

Hyalella armata (Faxon, 1876) was considered for a long time to be a monotypic species. The peculiar morphology, very distinct from other species in Lake Titicaca, was not analysed in detail after the original description. However, the present authors' study of an extensive collection from The Natural History Museum in London has revealed two morphologically distinct species. Descriptions of H. armata and the new species H. longispina are given. Diagnosis of Hyalella longispina n. sp. (Figs 1, 2): Body (Fig. 1) with a posterior dorsal transverse ridge on every segment. Coxae 1 to 4 acuminate. Coxa 4 excavated posteriorly, and with deep acumination at right angle to sagittal body plane. Lateral process of coxa 4 strongly elongate (Fig. 2), distance between left and right process apices longer than body length (that distance shorter than body length in H. armata). Eyes pigmented. Antenna 1 shorter than antenna 2. Antenna 2 less than half body length. Mandible incisor toothed. Maxilla 1 palp uniarticulate, longer than wide, reaching more than half the distance between base of palp and tip of setae on outer plate; inner plate slender, with two strong and pappose apical setae. Maxilla 2 inner plate with one strong pappose seta on inner margin. Gnathopod 1 propodus quadrangular (length less than twice maximum width), hatchet-shaped, inner face with more than ten pappose setae, distoposterior and distoanterior borders without setose scales. Gnathopod 2 propodus triangular, palm longer than posterior margin, slope oblique, anterior edge with a small process. Telson wider than long, apically rounded, with more than two short simple setae, arranged symmetrically on the apical margin. Lateroventral sternal gills present on segments 3 to 7. Types and locality: Holotype male, 10 mm; PERU, Lake Titicaca, Choccocoyo Bay, St. P 6, GIC 481, 11-23 m, leg. Crawford, 25.VI.1937. Paratypes (collecting data as holotype): allotype female, 9 mm; 106 males, 6-10mm; 93 females, 5-10 mm. All deposited at The Natural History Museum, London (holotype: 2002.311; allotype: 2002.312; other paratypes: 2002.313-322).

Indexción: Scielo Los crustáceos peracáridos comprenden un diverso grupo de invertebrados, comunes en ambientes terrestres, acuáticos dulceacuícolas y marinos. En este trabajo se revisa la diversidad de especies de los órdenes Amphipoda, Cumacea, Isopoda, y Tanaidacea, actualmente reportada para Chile. Otros grupos taxonómicos comúnmente incluidos en Peracarida no han sido citados aún para Chile. Presentamos en este trabajo una lista sistemática de los taxa de peracáridos y su distribución geográfica en Chile desde los 18°S hasta los 56°S, incluyendo el Archipiélago de Juan Fernández e Isla de Pascua. En un análisis preliminar, la distribución de las especies registradas para Chile sugiere que la diversidad de especies aumenta de norte a sur. El hecho que aún existen importantes areas geográficas con inusualmente bajos números de especies, y que muchas especies registradas para Chile tienen registros únicos, refuerza la necesidad de trabajos taxonómicos futuros, con el objeto de obtener un más adecuado conocimiento de la diversidad de especies de este importante grupo de invertebrados. Crustacean peracarids are a diverse group of invertebrates, common in terrestrial, freshwater and marine environments. The present study examines the species diversity of the orders Amphipoda, Cumacea, Isopoda, and Tanaidacea, presently reported from Chile. Other peracarid groups have not been recorded from Chile. A systematic list of presently recorded peracarid species and their geographic distribution in Chile from 18°S to 56°S, including the Archipelago of Juan Fernández and Isla de Pascua is provided. A preliminary biogeographic analysis suggests that species diversity increases from North to South. The facts that there are still large areas with unusually low number of species, and that many species recorded for Chile are unique records underlines the need for future taxonomic efforts in order to gain a thorough overview of the diversity of this important and species-rich group of invertebrates. Keywords: Peracarida, Amphipoda, Isopoda, Tanaidacea, Cumacea, Southwest Pacific

La fauna de anfipodos chilenos ha sido pobremente estudiada. En el caso de los de agua dulce y de ambientes epigeos, el grupo esta representado solo por un genero. Se reportan siete especies del genero Hyalella para Chile: H. simplex; H. fossamancinii, H. kochi; H. chiloensis; H. costera; H. araucana, y H. franciscae. Se entrega una breve diagnosis, una clave y figuras para cada especie

Hyalella pauperocavae n. sp. from Huancayo, Perú, is described. Five other epigean freshwater amphipods have been described from Peru (excluding Lake Titicaca), but the lack of type material and poor descriptions do not allow the assignment of the species described here to any of the names known for the area.

Two new species of hyalellid amphipods, Hyalella crawfordi and H. gauthieri, are described from Lake Titicaca; H. echinus (Faxon, 1876) is redescribed. The H. echinus group of species is newly proposed for these three species, and a group diagnosis is provided. A key to the three species in the group is provided Full article published online at http://www.senckenberg.de/odes/06-10.htm .

The taxonomy of gammaridean amphipods is poorly known in Chile. The lack of literature has discouraged investigation of this group, which has been overlooked for years. This has led to the exclusion of amphipods from biological and ecological studies done in our country. I present here a preliminary report on the actual state of the group with reference mainly to its taxonomy, ecological studies and a species catalogue. I have only included species from continental Chile north of 56 °S, Juan Fernandez Archipelago and Isla de Pascua. Species from Chilean Subantarctic and Antarctic waters are excluded, because they are well covered by other authors. There are 168 known for Chile, 36 of them undescribed or with their status not clear. This report is based on a revision of the species recorded for Chile, analysis of samples from the Chilean coast and the work of ecologists who are using the group as material for study.