''Nesiarchus nasutus'', the Black gemfish, 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
snake mackerel
The snake mackerel (''Gempylus serpens'') is the sole species of fish in the monotypic genus ''Gempylus'', belonging to the family Gempylidae (which is also referred to generally as "snake mackerels"). It is found worldwide in tropical and sub ...
found in tropical and subtropical waters in most parts of the world, though not in east Pacific and north Indian waters. It occurs at depths of from though they make
diel vertical migration
Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24-h ...
s from
benthopelagic to
mesopelagic depths at night. This species can reach a length of
SL though most do not exceed SL. It is of minor importance to local
commercial fisheries. This species is currently the only known member of 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 ...
, ''Nesiarchus''.
That genus is thus considered
monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
.
References
Mackerels
Gempylidae
Fish described in 1862
Monotypic fish genera
Taxa named by James Yate Johnson
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