Redescription of Hyalella Azteca from Its Type Locality, Vera Cruz, Mexico (Amphipoda : Hyalellidae)

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 Musdum d'Histoire Naturelle, Ville de Geneve, Switzerland. Hyalella Smith, 1874, is known only from the Nearctic and Neotropical biogeographical regions. Forty-four species have been described. One of the species, Hyalella azteca (Saussure, 1858), is considered to be a common freshwater organism found all over North America, Central America, and northern South America. The original description by Saussure (1858), based on samples from a "cistern" in Vera Cruz and Ciudad de Mexico, Mexico, is poorly described and figured. In North and Central America, most of the freshwater species of Hyalella recorded are assigned to Hyalella azteca; however, seven other related species are known from the region: H. texana Stevenson and Peden, 1973, from Clear Creek Spring, Texas; H. montezuma Cole and Watkins, 1977, from Montezuma Well, Arizona; H. squamosa Mateus and Mateus, 1990, from Guadeloupe, West Indies; H. caribbeana Bousfield, 1996, from Riviere Bell Eau, Grande Terre Guadeloupe, West Indies; H. longicornis Bousfield, 1996, from St. George's Golf course, Kenilworth?, Utah; H. muerta Baldinger, Shepard, and Threloff, 2000, from California, U.S.A. (hypogean); and H. sandra Baldinger, Shepard, and Threloff, 2000, from California, U.S.A. The first putative species of Hyalella from North America was described as early as 1818 by Say from marshes in South Carolina as Ampithoe dentata. Stebbing (1906) synonymized this species under Hyalella azteca. Later, Bousfield (1958) attributed Ampithoe dentata to Crangonyx serratus (Embody, 1910). Bate (1862) defined Allorchestes knickerbockeri from material deposited in the British Museum, collected by Say in North America and labeled as Gammarus minus. Smith (1874) described the new genus Hyalella based on Allorchestes knickerbockeri Bate, 1862, Amphithoe azteca Saussure, 1858, and his own material from the United States. He also described a new species, H. dentata, collected from several places in the United States from Oregon to Maine. This species is considered to be different from H. knickerbockeri (Bate, 1862). One year later Smith (1875) redescribed the genus Hyalella and H. dentata and added a new species from Colorado, U.S.A., H. inermis Smith, 1875. Harford (1877) described Lockingtonia fluvialis from Lobos Creek, California, U.S.A., and most likely was unaware of the work of Smith (1874, 1875). For many years the name Hyalella was not used after it was synonymized under Allorchestes by Faxon (1876). Stebbing (1903) described Hyalella faxoni from Costa Rica and reestablished the genus name. Stebbing (1906) synonymized H. knickerbockeri (Bate, 1862), H. dentata, H. inermis, and Lockingtonia fluvialis under H. azteca, but did not mention H. faxoni. Weckel (1907) put H. faxoni in the synonymy of H. knickerbockeri, which she thought had precedence over H. dentata Smith, 1874. She