At some point Chasmogenus was considered a subgenus of Helochares, and according to Hebauer (1992), the species of Chasmogenus can be separated in two groups (subgenera): Chasmogenus sensu stricto (composed of the American species with 8 antennomeres and simple aedeagus) and the Chasmogenus Crephelochares (composed by the non American species with 9 antennomeres and "more differentiated" aedeagus). Regarding distributions, 17 species are Afrotropical, 5 Oriental, 3 Palaearctic and 15 Neotropical (see Hansen 1999). Hebauer also mentions affinities of Chasmogenus with Enochrus, which at this time is placed in a separate subfamily (see Short & Fikáček 2013).
As it happened with Helobata, the external morphology of Chasmogenus is very homogeneous, but not as extreme, so I started my matrix with the characters used by Short (2007) on the second chapter of his Dissertation: "Systematics and biology of the endemic water scavenger beetles of Hawaii (Coleoptera: Hydrophilidae)", which contains 55 characters, most of them associated with external morphology, knowing that it is very likely that not all the characters might be informative for my group. I also included characters from Hebauer (1992) and Clarkson & Ferreira (2014).
Then I selected specimens in order to start coding them on the matrix. The group of specimens at this time includes one species of Enochrus, Helobata striata, some Helochares, Chasmogenus abnormalis from Okinawa (Japan), Chasmogenus nitescens from New Caledonia, Chasmogenus ruidus from Costa Rica, and 26 unidentified Chasmogenus specimens (very likely different species, most of them undescribed) from Nicaragua, Costa Rica, Panama, Ecuador, Venezuela, Guiana, Suriname, French Guiana, Bolivia and Paraguay.
When I started looking at the specimens to code them, and as it usually happens while doing this, more characters and character states started to appear. Then I had to go back to the very useful drawings presented by Hansen (1991) and his list of characters, and at the same time get used to the terminology employed by some authors (e.g. mesoventrite to refer to the mesosternum). I have been also producing my own drawings in order to help me understand the variations and keep track of what I saw. Here are some of my schemes.
As of now, the matrix has 167 characters (86 binary). I know several are not going to be informative (either because all of the specimens have the same character state, or because they doesn't exhibit a clear signal) but also as soon as I start dissecting (mouthparts, wings, abdomen, male and female genitalia), many more characters are going to be added. I can't wait for that to happen!. Here is a screenshot of the matrix as it is now.
For now I need to keep coding the remainder taxa, as you can see I have only 3 out of the 26 specimens I selected, in part because every time I'm coding one specimen, new character states appear and I have to go back through all the other specimens that are already in the matrix in order to figure out the best way to code the character states, but at this time the matrix it's getting more stable.
References
- Clarkson, B., & Ferreira, N. (2014). Four new species and first nominal record of Chasmogenus Sharp, 1882 (Coleoptera: Hydrophilidae) from Brazil. Zootaxa, 3765(5), 481-494.
- Hansen, M. (1991). The hydrophiloid beetles. Phylogeny, classification and a revision of the genera (Coleoptera: Hydrophilidae). Biologiske Skrifter, 40, 1–367.
- Hansen, M. (1999). World catalogue of insects. Volume 2: Hydrophiloidea (s. str.)(Coleoptera). Apollo Books.
- Hebauer, F. (1992). The species of the genus Chasmogenus Sharp, 1882 (Coleoptera: Hydrophilidae). Acta Coleopterologica, 8(2), 61-92.
- Short, A. E. Z., & Fikáček, M. (2013). Molecular phylogeny, evolution and classification of the Hydrophilidae (Coleoptera). Systematic Entomology, 38(4), 723-752.
- Short, A. E. Z. (2007) Phylogeny, morphology, and biology of the hydrobiusine and hydrophiline water scavenger beetles (Coleoptera: Hydrophilidae: Hydrophilini). Ph.D. Dissertation, Cornell University. 219 pp.
