Cymadusa Hughes & Peart, 2013, comb. nov.
Creators: name: Hughes, Lauren E.
name: Peart, Rachael A.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Ampithoidae
Cymadusa

description: 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.
description: Published as part of Hughes, Lauren E. & Peart, Rachael A., 2013, New species and new records of Ampithoidae (Peracarida: Amphipoda) from Australian Waters, pp. 1-102 in Zootaxa 3719 (1) on pages 4-5, DOI: 10.11646/zootaxa.3719.1.1, http://zenodo.org/record/246657