Elasmopus, Costa, 1853

Lowry, J. K. & Hughes, L. E., 2009, Maeridae, the Elasmopus group *, Zootaxa 2260 (1), pp. 643-702 : 644-645

The Elasmopus group

The Elasmopus group was originally proposed by J.L. Barnard (1972a: 239) within the family Gammaridae . He included four genera: Elasmopus Costa, 1853 , Ifalukia J.L. Barnard, 1972a , Mallacoota J.L. Barnard, 1972a and Parelasmopus Stebbing, 1888 . Later Lowry & Fenwick (1983) included a fifth genus, Hoho . In this paper we include two additional genera, the enigmatic Beaudettia J.L. Barnard, 1965 , originally placed in its own family, but later placed in the ‘ceradocid’ group of Barnard & Barnard (1983), and Spathiopus Thomas & Barnard, 1985a .

The expanded Elasmopus group is characterised by well developed eyes, a cheek notch/slit on the side of the head and a rounded or subacute anteroventral corner, a short to minute accessory flagellum, a distomedial flap on the third article of the maxillipedal palp, an anteroventrally produced coxa 1, pleonites and urosomites without dorsally serrate posterodistal margins and a third uropod with well developed rami which are never more than twice the length of the peduncle.

Other characters which appear in some taxa within the Elasmopus group genera include: pairs of dorsal carinae on pereonite 7 to urosomite 1 ( Parelasmopus , Mallacoota ); a pair of dorsal carinae on the first urosomite only ( Mallacoota , Hoho ); a 1-articulate mandibular palp ( Hoho , Ifalukia ) and a falcate mandibular palp ( Elasmopus , Spathiopus ). In particular, the 1-articulate mandibular palp separates Hoho from Mallacoota and Ifalukia from Elasmopus . The falcate mandibular palp separates Elasmopus and Spathiopus from all other taxa. The bicarinate urosomite 1 separates Hoho , Mallacoota and Parelasmopus from Beaudettia , Elasmopus , Ifalukia and Spathiopus . In four Indo-West Pacific species of Elasmopus ( E. integer Myers, 1989 , E. pseudinteger Appadoo & Myers, 2003 , E. takamotus Myers, 1986a and E. visakhapatnamensis Kanakadurga, Rao & Shyamasundari, 1982 ) the telson is entire. Beaudettia palmeri J.L. Barnard, 1965 , also has an entire telson. In two species ( Elasmopus neglectus Chilton, 1915 and E. japonicus Stephensen, 1932 ) there is a single carina on urosomite 1. Therefore it appears that within the Elasmopus group there is the potential for reevaluation of current generic divisions based on at least the morphological structures mentioned above.

Considering the three Elasmopus group genera which occur on the Great Barrier Reef: Elasmopus is widespread and speciose in tropical and temperate environments worldwide; Mallacoota occurs throughout the Indo-West Pacific and in the Caribbean area and Parelasmopus is a small genus, endemic to the Indo-West Pacific. The remaining, non-GBR genera are smaller with more restricted distributions. Beaudettia and Ifalukia are both monotypic genera, apparently endemic to Micronesia and Spathiopus is endemic to the Caribbean area. Hoho is confined to southern Australia and southern New Zealand.

Berents (1983) reported eight species from Lizard Island, five species of Elasmopus , one species of Mallacoota and two species of Parelasmopus . We report 15 species, including two new species of Elasmopus – one originally identified as E. pocillimanus Bate (1862) by Berents (1983), five additional species of Mallacoota and two species of Parelasmopus – one of which was originally identified by Berents (1983) as P. echo J.L. Barnard (1972a) .

Two species of Elasmopus are apparently endemic to the tropical Australia ( E. spinicarpus Berents, 1983 and E. varanocephalensis sp. nov.), and five species are widespread in the Indo-West Pacific ( E. alalo Myers, 1986b , E. crenulatus Berents, 1983 , E. hooheno J.L. Barnard, 1970 , E. pectenicrus (Bate, 1852) ; E. slatyeri sp. nov.). Three species of Mallacoota are apparently endemic to tropical Australia ( M. balara Berents, 1983 , M. chandaniae Lowry & Springthorpe, 2005 and M. scopulosa sp. nov.) and three species occur elsewhere in the Indo-West Pacific ( M. capricornia sp. nov., M. nananui Myers, 1985 , M. schellenbergi Ledoyer, 1984 ). Both species of Parelasmopus are apparently endemic to tropical Australia ( P. cymatilis sp. nov., P. suensis ( Haswell, 1879b)) .

The Elasmopus group is relatively well known in tropical (15 species) and temperate (18 species) Australia (current study; J.L. Barnard 1972a; Lowry & Springthorpe 2005). At present there appears to be no species overlap between these areas within Australia.