The subgenus Rivulus is now containing 3 species only. Two from the Caribbean island Cuba and 1 found on Haiti. The latter is believed to be member of the subgenus but that need further conformation. These species differ from the members of other subgenera in the genus Rivulus by having the hypural plate completely fused (versus not fully fused in all other subgenera.)
Rivulus s.s. is one of the 10 subgenera in Rivulus so far with: Anablepsoides, Atlantirivulus, Benirivulus, Cynodonichthys, Laimosemion, Oditichthys, Owiyeye, Melanorivulus, and Vomerivulus, being the other subgenera.
Rivulus cylindraceus was the first Rivulus described ever in the then monotypich genus (Poey 1860).
From North-Eastern Cuba Rivulus berovidesi (Ponce de Leon et al. 2014) was described.
From the island "Pine - Island" just south from the Cuba coast another species (Rivulus insulaepinorum) was known but was synonymized with R. cylindraceus in the same paper where R. berovidesi was described. (Ponce de Leon et al. 2014.)
Members of the subgenus Rivulus might be close related to Kryptolebias. They share a more than random melanistic pigment and I suggest they share the same ancient ancestor. A deepened study could allow us to unravel this relationship.
The island Cuba inhabits Kryptolebias marmoratus, a hermaphrodite species that is found in marine and brackish waters along the shores of the caribbean islands and along the mainland as well.
Poey, F., 1860 [1858-1861] Memorias sobra la historia natural de la Isla de Cuba, acompañadas de sumarios Latinos y extractos en Francés. Tomo 2. La Habana. Entrega secundo [= second delivery], including Poissons de Cuba. Espèces nouvelles: 115-336, pls. 10-12 and 14
Trewavas, E. 1948. Cyprinodont Fishes of Santo Domingo, Island of Haiti. Proc. Zool. Soc. London, 118: 408, pl. 1 (fig. 1-2).
Huber, J.H. 1992. Review of Rivulus. Ecobiogeography - Relationships. Cybium Suppl., Société Française d'Ichtyologie Publ.: 586 pp., 40 pls., 85 figs., 8 tabs, 13 maps.
Costa, W.J.E.M. 2006f. Relationships and Taxonomy of the killifish genus Rivulus (Cyprinodontiformes: Aplocheiloidei: Rivulidae) from the Brazilian Amazonas river basin, with Notes on historical Ecology. Aqua, Journal of Ichthyology and Aquatic Biology, 11 (4): 133-175, 45 figs.
Costa, W.J.E.M. 2011c. Phylogenetic position and taxonomic status of Anablepsoides, Atlantirivulus, Cynodonichthys, Laimosemion and Melanorivulus (Cyprinodontiformes: Rivulidae). Ichthyological Exploration of Freshwaters (Ichthyol. Explor. Freshwaters), 22 (3): 233-249, 1 fig., 1 tab.
Huber, J.H. 2012b. Reappraisal of the Phylogeny of Rivulus and its Allied focused on External Characters. Killi-Data Series 2012, 9-25, 3 figs., 2 tabs.
Vermeulen, F.B.M. 2015b. The Killi's of the lost World. New World Killi Series, Pastelaria studios, vol. 1: 168 pp., figs.
Ponce de Leon J.L., Gunnary L., Rodriguez R., Metcalfe C.J., Hernandez D., Casane D., Garcia-Machado E. 2014. Phylogeography of Cuban Rivulus: Evidence for allopatric Speciation. Mol. Phyl. Evol., 79: 404–414, figs.
See the species pages of this subgenus.