Hughes, Lauren E. & Peart, Rachael A., 2013, New species and new records of Ampithoidae (Peracarida: Amphipoda) from Australian Waters, Zootaxa 3719 (1), pp. 1-102: 4-5

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Cymadusa   and Paragrubia  

The genus Paragrubia   was established by monotypy for Paragrubia vorax (Chevreux, 1901)   . Paragrubia   was originally diagnosed by the following features: gnathopod 1 is more robust than gnathopod 2, the antenna 1 accessory flagellum is multi-articulate and the telson is subovate. Three characters separated Paragrubia   from the closely related genus Cymadusa   in which gnathopod 1 is smaller than gnathopod 2, the accessory flagellum has only 1 -article and the telson was less rounded.

Conlan (1983) expanded the diagnosis of Cymadusa   to include a multi-articulate accessory flagellum to accommodate C. uncinata (Stout, 1912)   . However, this was later overlooked in the synonymy and generic diagnoses proposed by Barnard & Karaman (1991) and also Poore & Lowry (1997). In Poore & Lowry (1997), two species with a multi-articulate accessory flagellum on antenna 1, P. uncinata   and P. variata   , were transferred into Paragrubia   . Consequently, the diagnosis of Paragrubia   was expanded to include gnathopod 1 larger or stouter or subequal in size to gnathopod 2 to accommodate these two species. Cymadusa   was also diagnosed to include gnathopod 1 as smaller than or subequal to gnathopod 2, which created overlap between gnathopod characterization of Paragrubia   and Cymadusa (Poore & Lowry 1997)   . Currently, the two characters used to separate Cymadusa   from Paragrubia   are the relative sizes of gnathopods 1 and 2, and the number of articles in the antenna 1 accessory flagellum.

In an assessment of new and known species that best correspond to the ampithoid genera Cymadusa   and Paragrubia   , the number of articles in the antenna 1 accessory flagellum range from scale-like to 1, 3, 4, 6, 7 and 10, forming an almost continuous series. As there is no clear break in the range of articles present, delimiting the two genera based on the number of articles would be largely arbitrary. A mutli-articulate accessory flagellum was initially thought to be only associated with gnathopod 1 dominance over gnathopod 2; however, new species as well as previously described species do not conform to this pattern. The opposing character combinations of a uniarticulate flagellum with dominant gnathopod 1 and a multi-articulate flagellum with dominant gnathopod 2 are now recognised among the new species identified here.

Presently gnathopod 1 and 2 sizes are assessed in relation to one another, gnathopod 1 is larger than gnathopod 2, gnathopod 1 is smaller than gnathopod 2, gnathopod 1 is subequal to gnathopod 2. This character delineation does not acknowledge the independence in development of these limbs. Within the newly described species, gnathopod 1 is enlarged ( P. apoorei   ), but also gnathopod 2 is reduced ( P. springthorpei   ). Equally, for species where gnathopod 1 and 2 are of similar size, they may both be enlarged or both reduced ( Paragrubia pilipes   and Cymadusa bilobata   , respectively).

We propose that the enlargement of gnathopod 1 and 2 be assessed separately. As independent characters, gnathopods may be either feeble/diminutive or stout/robust. This new character concept more clearly defines the generic diagnosis of Cymadusa   from Paragrubia   within the Ampithoidae   . The relative size difference of gnathopod 1, in comparision to gnathopod 2, is now considered to be of secondary importance. This subtle but important shift in character emphasis removes previous taxonomic ambiguity between Cymadusa   and Paragrubia   . The enlargement or reduction of gnathopods 1 and 2 is recognised as having generic level importance elsewhere in the Corophiidira ( Aoridae   ), but limited/poor character description and assessment has hampered the recognition of this generic level character within the Ampithoidae   . The enlargement or reduction in the gnathopods is considered here, also, to be of generic importance for the Ampithoidae  

Based on the above character information gained from the new species, the current generic diagnosis suggested by Lowry & Poore (1997) is no longer appropriate. Cymadusa   is rediagnosed to accommodate species with either a scale-like, 1, 2 or multi-articulate accessory flagellum; gnathopod 1 not stout or robust; gnathopod 1 smaller or subequal to 2; gnathopod 1 palm acute; pereopods 5–7 normal to prehensile and uropod 1 with distoventral spine; and telson trapezoidal.

Paragrubia sensu Chevreux (1901)   is reinstated here and expanded: gnathopod 1 enlarged to appear stout/ robust; gnathopod 1 is more robust than gnathopod 2. The antenna 1 accessory flagellum is present, and either single or multi-articulate. The diagnosis is expanded to include both subovate and trapezoidal telson shapes.

This new diagnosis for Paragrubia   affects the placement of three previously described species. Ampithoides mahafalensis   Ledoyer, 1967 previously in Cymadusa   is transferred to Paragrubia   based on the robust gnathopod 1. Acanthogrubia uncinata Stout, 1912   , placed in Paragrubia   by Shoemaker (1941) and Poore & Lowry (1997), is now transferred back to the Cymadusa   based on the gnathopod 1 being smaller than gnathopod 2. Lastly, Grubia variata Sheard, 1936   is transferred from Paragrubia   as designated by Poore & Lowry (1997) back to Cymadusa   based on the feeble/diminutive gnathopod 1, which is also smaller than gnathopod 2. The new combinations for these taxa are P. mahafalensis   comb. nov., C. uncinata   comb. nov. and C. variata   comb. nov.