Eutrigaster Cognetti de Martiis 1904

Genus Eutrigaster Cognetti de Martiis, 1904 Remarks. The genus Eutrigaster was erected to accommodate E. oraedivitis Cognetti de Martiis, 1904 based on the presence of three gizzards in an otherwise benhamiid earthworm. However, the structure that Cognetti de Martiis (1904) thought to be the first gizzard is in reality an enlarged semi-muscular proventriculus (Sherlock et al. 2011). Sims (1987) expanded the genus to include Neotropical dichogasterid species without penial setae and later, Csuzdi & Zisci (1991) revised Eutrigaster and redefined it to species with a semi-muscular enlarged proventriculus in segment 5, and two gizzards in segments 6–7. Csuzdi & Zicsi (1991) divided the genus into two subgenera for species with (Graffiona Csuzdi, 2014) or without penial setae (Eutrigaster). The classification suggested by Csuzdi & Zicsi (1991) transferred most Neotropical Dichogaster to Eutrigaster, with a few species still retaining their position within Dichogaster. Therefore, the only distinguishing characteristics between Eutrigaster and the predominantly African Dichogaster are that the latter lacks an enlarged proventriculus, and its gizzards are located in segments 5–6. However, several authors disagree with the validity of Eutrigaster as currently described (e.g., Fragoso & Reynolds 1997; James 1996, 2004; James & Gamiette, 2016). Firstly, the location of the gizzards is frequently variable in the literature and is very difficult to accurately determine as septae in this region are extremely thin and can break without leaving evident traces (Fragoso & Reynolds 1997). Secondly, the degree of enlargement and musculature of the proventriculus seems to be a function of body size rather than evolutionary history (James 1996). Interestingly, the Neotropical Dichogaster-Eutrigaster species seem to be unrelated to the Pantropical Dichogaster clades based on molecular phylogenetic inferences (Anderson et al. 2017). Here, we keep the Hispaniolan native dichogasterid species in Eutrigaster for consistency purposes, but recognizing that a revision of this group is needed and that changes in the current classification of both Eutrigaster and Dichogaster and their subgenera are likely to occur through the application of phylogenetic and phylogenomic analyses.