The species belonging to Ctenosta are distinct from other species of the phyletic line Castrida - Caminara (sensu Jeannel, 1940) for the loss of the basal seta that in the others exists close to hind angles of the pronotum.
In all species of the subgenus Ctenosta, invariably, the hind angles of the pronotum are quite obliterated and the sculpture of elytra is characterized by 16 intervals on each of them; that means having a single tertiary interval on the sides of a secondary one ("triploïde" type). Also all the intervals are always distinctly separated by the striae.
The subgenus Ctenosta has a characteristic Indo-African spreading, already detected and discussed by Jeannel (1940; 1961) from the biogeographic point of view. In fact Ctenosta is specific to Africa including the island of Madagascar, where there are two endemic species, but it is also present in the Indian peninsula where we find another endemic species. This distribution seems consistent with the hypothesis of a differentiation before the separation of India from the African continent. This hypothesis has been advanced by Jeannel (1961: 20) for some groups of Carabidae with a similar distribution but it is undermined by the results of recent genetic studies (Su et Al., 2005) that seem to indicate that the origin of Calosomatina is much more recent than what had been previously hypothesized.
Moreover Jeannel (1940) had considered Aplothorax burchelli Waterhouse 1842 from island of St. Helena being closely related to Ctenosta, based on phylogenetic considerations. On the contrary, according to Basilewsky (1972) it would be a quite distinct entity that should be attributed to a specific tribe (Aplothoracini), due to the characteristics of the male genitalia and due to the external morphology of the adult and mainly of the larva.
Later on, Aplothorax burchelli was placed again as a separate genus inside of the subtribe Calosomatina, by reverting to the primacy of the phylogenetic considerations (Prüser and Mossakowski 1998: 300). This position seems to be further confirmed by Sota & al. (2020) that, according to a phylogenetic analysis of mitogenome sequences, believe that A. burchelli might constitute a monophyletic group with the Ctenosta species from Africa. Finally Toussaint & al. (2021), again using phylogenomics techniques, propose the synonymy of Aplothorax resulting in the new combination Calosoma (Ctenosta) burchelli.
However, also wanting to take the results of the genetic analysis into account. we think that Basilewsky's arguments are difficult to surmount, particularly as for what regards the unique larval morphology of Aplothorax burchelli. Consequently, at least for the moment, we prefer not to include it inside Calosomatina.