Atergatis obtusus A. Milne-Edwards 1865

Atergatis cf. obtusus A. Milne-Edwards, 1865 Fig. 90 Material examined MAURITIUS • 1 ♀ (35.6 ×23.0); 1885; Pere Antiga leg.; MNCN20.04/04377. Remarks The specimen was previously identified as Actaea laevigatus, a species name combination that has not been found in literature and is possibly due to a misspelling. The key provided by Serène (1984) leads to Atergatis laevigatus A. Milne-Edwards, 1865 (cw/cl = 1.6−1.7) and A. obtusus (cw/cl = 1.5), since our specimen ratio is at 1.54. According to Serène, it would not be any of these two species. However, Takeda & Marumura (1997) published that the carapace proportions of the genus Atergatis varied with the size of the specimens; subsequently, Maenosono (2022) identified a specimen as A. obtusus with a ratio of 1.54. Takeda & Marumura (1997) also observed that A. laevigatus has a prominently projecting anterolateral margin (shoulder), whereas A. obtusus does not, as Takeda & Marumura (1997) named it “sloping shoulder”. Our specimen agrees with the sloping shoulder shape. Subsequent to Serène (1984), the species Atergatis interruptus Takeda & Marumura, 1997 was described, which in its description take its place between A. laevigatus and A. obtusus based on the proportions. However, the posteriolateral edge is interrupted, which does not occur in our specimen. This species has few records, and was previously recorded in Thailand, Vietnam, Philippines and Japan (A. Milne-Edwards 1865; Lai et al. 2011; Maenosono 2022). If the identification is confirmed in the future, this work would provide the first record of A. obtusus in waters of Mauritius, and extend the distribution range for this species. This new citation, far from its known distribution area, would not be exceptional, as many other species in the Indian Ocean have very broad distributions. However, due to all the previously mentioned points, it is possible that there are very closely related “twin” species that have not yet been described, and a molecular approach could solve heir taxonomic status. For identification, see also A. Milne-Edwards (1865), Serène, (1984), Takeda & Marumura (1997) and Maenosono (2022).