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The order Lophogastrida is a relatively small group of malacostracan crustaceans, consisting of about 55 pelagic and bottom-associated deepwater species, formerly contained as a suborder within the Mysidacea. Both the orders Mysida and Lophogastrida are shrimplike in appearance , and because the ovigerous females carry developing embryos in a ventral brood pouch, from which their developed juveniles emerge, they are often referred to as “opossum shrimp.” Lophogastrids have a worldwide oceanic distribution. Members feed principally on zooplankton but are also known to have a raptorial feeding habit, and some species appear to be bottom scavengers. Compared to the Mysida, members of the order are relatively large (1–8 cm) with at least one species, Gnathophausia ingens, reaching lengths of 35 cm (Mauchline 1980, Schram 1986, Brusca and Brusca 2003). Lophogastrida are defined by the combination of the following morphological characteristics: (1) welldeveloped carapace extending over most or all of thorax, fused to no more than the anterior 4 thoracic somites; (2) right mandible without lacinia mobilis; (3) thoracopod 1 forming a maxilliped; (4) thoracomere 1 not separated from the head by an internal skeletal bar; (5) gills present on most thoracopods; (6) marsupium with 7 pairs of oostegites; (7) well-developed, biramous pleopods in both sexes, male pleopods not modified; (8) statocysts absent on uropodal endopods (W. Tattersall 1951, Schram 1986, Nouvel, Casanova, and Lagardère 1999, Brusca and Brusca 2003, Richter 2003). Banner (1954), in his synopsis of the Mysidacea of the Gulf of Mexico (GMx), listed 3 species of lophogastrids, Lophogaster americanus Tattersall, 1951, L. longirostris, and Gnathophausia ingens. Lophogaster americanus is now considered a synonym of L. longirostris (see O. Tattersall 1960). Gnathophausia zoea was not included in Banner’s list, but was reported by Tattersall in 1951 from 2 locations in the Gulf. Since 1954, 6 additional species have been recorded from Gulf waters in taxonomic, ecological, and distributional reports. Eucopia grimaldii, E. australis (= E. major Hansen, 1910 [see Fage 1942, O. Tattersall 1955]), E. sculpticauda, E. unguiculata, Chalaraspidum alatum, and Gnathophausia gracilis were collected with shrimp trawls (Springer and Bullis 1956) and Tucker trawls (Hopkins and Lancraft 1984, Hopkins et al. 1994) in the northeastern Gulf of Mexico. Additionally, Spears et al. (2005) used Gnathophausia zoea, Gnathophausia ingens, and Eucopia sp. (identified to E. unguiculata by K. Meland) from the GMx in their studies on peracarid 923 52 Lophogastrida (Crustacea) of the Gulf of Mexico W. Wayne Price, Richard W. Heard, Pål Aas, and Kenneth Meland  Lophogastrida. After Faxon 1895. 924 ~ Lophogastrida (Crustacea) of this family is still highly subjective. In 1992, Petryashov, based on morphological evidence and an earlier discussion by O. S. Tattersall (1955), transferred Gnathophausia gigas and G. ingens to a new genus Neognathophausia . Casanova, De Jong, and Faure (1998) examined the relationships of the Lophogastridae and Eucopiidae using morphological and molecular data from species of Gnathophausia and Eucopia. Their results showed a sister-group relationship between G. gracilis and all other Gnathophausia that included a monophyletic G. gigas and G. ingens group. Following these results, the exclusion of both of these species from the Gnathophausia would make the genus Gnathophausia paraphyletic. Casanova, De Jong, and Faure (1998) rejected the genus Neognathophausia and also concluded that the Eucopiidae originated from the Lophogastridae. Most Gulf of Mexico records for the order are based on specimens collected in mid- or deepwater trawls. The taxa thus far identified from Gulf waters are cosmopolitan species , and with the possible exception of Lophogaster longirostris , are pelagic. Relatively little epibenthic and hyperbenthic sampling has been done in the Gulf region, and most that has been done has not utilized gear such as epibenthic sledges with fine-mesh netting, gear suitable for exploring the bottom fauna and consequently recording the possible presence of bottom-living lophogastrids. The only published studies in which bottom trawls or dredges were used were those of Springer and Bullis (1956), Tattersall (1951), and Faxon (1896), but this gear was apparently more suited (mesh size) for the collection of larger crustaceans, such as decapods . This possible artifact of sampling may be the reason that only one species of Lophogaster, a genus containing some hyperbenthic species (e.g., Lophogaster typicus (Tattersall and Tattersall, 1951)), is presently known from the region. It would be useful in future deep-water sampling in the Gulf if epibenthic sledges could also be employed as part of the general sampling regime. At present there are no known endemic species of Lophogastrida from the Gulf of Mexico (see the taxon summary...

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