The Mexican rivulus (''Millerichthys robustus'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of killifish from the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Rivulidae which is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

where it is found in the

Papaloapan The Papaloapan River () is one of the main rivers of the Political divisions of Mexico, Mexican state of Veracruz (state), Veracruz. Its name comes from the Nahuatl ''papaloapan'' meaning "river of the Butterfly, butterflies". In 1517, Juan de Gri ...

and

Coatzacoalcos River The Coatzacoalcos is a large river that feeds mainly the south part of the state of Veracruz; it originates in the Sierra de Niltepec and crosses the state of Oaxaca in the region of the Isthmus of Tehuantepec, flowing for toward the Gulf of M ...

basins. This annual killifish grows to a

total length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish ...

of . It is the only known species in its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

, but its exact

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

position remains uncertain, as it has not been included in any

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

study. This species was described by Robert Rush Miller and Carl Leavitt Hubbs as ''Rivulus robustus'' in 1974, it was reclassified in the monotypic genus ''Millerichthys'' in 1995, the generic name honouring Robert Rush Miller.

References

Rivulidae Endemic fish of Mexico Freshwater fish of Mexico Fish described in 1974 Taxa named by Robert Rush Miller Taxa named by Carl Leavitt Hubbs {{Cyprinodontiformes-stub