Eucalliaxiopsis Sakai 2011

Genus Eucalliaxiopsis Sakai, 2011 TYPE SPECIES. — Eucalliax cearaensis Rodrigues & Manning, 1992, by original designation and monotypy. INCLUDED FOSSIL SPECIES. — Eucalliaxiopsis alabamensis (Rathbun, 1935a) n. comb.; E. pseudorakosensis (Lőrenthey in Lőrenthey & Beurlen, 1929). DIAGNOSIS. — See Sakai (2011: 503, 504). REMARKS The assignment of Callianassa alabamensis Rathbun, 1935, to Eucalliaxiopsis is based on the combination of the following characters: a subquadrate manus, a triangular fixed finger with an oblique longitudinal ridge, and a smooth lower margin of cheliped merus. The oblique longitudinal ridge is also present in Calliaxina Ngoc-Ho, 2003 (Hyžný 2012; Poore 2021), but it is accompanied by a lateral concavity in the minor chela in this genus (Hyžný 2012), a character which is not identified in C. alabamensis. In Calliaxina, the lower margin of the cheliped merus has denticles (Poore 2021), whereas it is smooth in C. alabamensis. The observed variation of two morphotypes of cheliped dactylus in C. alabamensis corresponds to differences between major and minor claws as exemplified in extant species of Eucalliaxiopsis (Poore 2021). At least some fossil species of Eucalliax Manning & Felder, 1991, as listed by Schweitzer et al. (2010) and Hyžný & Klompmaker (2015), probably belong to Eucalliaxiopsis. This is because they were assigned to Eucalliax largely based on similarities with some extant species, previously classified within Eucalliax. Recent revisions (Poore et al. 2019; Robles et al. 2020; Poore 2021) recognized the genus Eucalliax to be monotypic, with the only extant representative being its type species, E. quadracuta (Biffar, 1970), while the species previously treated under Eucalliax were reassigned to other eucalliacid genera. In this respect, Hyžný & Dulai (2021) reassigned Eucalliax pseudorakosensis (Lőrenthey in Lőrenthey & Beurlen, 1929) from the Miocene of Central Europe to Eucalliaxiopsis. Other fossil species of Eucalliax are still pending revision.