Nannoptopoma is a small genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of catfish

Catfish

Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

es (order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Siluriformes) of the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Loricariidae

Loricariidae

Loricariidae is the largest family of catfish , with almost 700 species and new species being described each year. Loricariids originate from fresh water habitats of Costa Rica, Panama, and tropical and subtropical South America. These fish are noted for the bony plates covering their bodies and...

. This genus includes two species, N. spectabile and N. sternoptychum.

Taxonomy

Nannoptopoma is classified within the tribe Hypoptopomatini of the subfamily Hypoptopomatinae

Hypoptopomatinae

Hypoptopomatinae is a subfamily of catfishes of the family Loricariidae.Hypoptopomatinae is a monophyletic assemblage within the family Loricariidae. It is composed by 17 genera and approximately 80 species. This subfamily represents about one-tenth of all loricariid species.It is divided into two...

. It is most closely related to the genus Hypoptopoma

Hypoptopoma

Hypoptopoma is a genus of catfishes of the family Loricariidae.-Taxonomy:The genus was established by Albert C. L. G. Günther in 1868 for his new species H. thoracatum, on the basis of the peculiar, depressed, spatulate formation of the head with the eyes on the lateral edges of the head...

with which it has a sister group

Cladistics

Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...

 relationship.

Distribution

N. spectabile is known from the upper Amazon

Amazon River

The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...

 and Orinoco basins of Colombia

Colombia

Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...

, and N. sternoptychum is known from the lower Amazon River basin and tributaries below 200 metres (660 ft) elevation

Elevation

The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....

.

Physical description

Nannoptopoma differs from other members of the subfamily Hypoptopomatinae by osteological

Osteology

Osteology is the scientific study of bones. A subdiscipline of anatomy, anthropology, and archeology, osteology is a detailed study of the structure of bones, skeletal elements, teeth, morphology, function, disease, pathology, the process of ossification , the resistance and hardness of bones , etc...

 differences. They have no adipose fin, a greatly depressed snout and head, eyes visible from below, and a body that is not elongate or depressed. This genus is most similar in external appearance to Hypoptopoma

Hypoptopoma

Hypoptopoma is a genus of catfishes of the family Loricariidae.-Taxonomy:The genus was established by Albert C. L. G. Günther in 1868 for his new species H. thoracatum, on the basis of the peculiar, depressed, spatulate formation of the head with the eyes on the lateral edges of the head...

, though Nannoptopoma species lack pectoral fin spine serrae characteristics of Hypoptopoma and have a shorter, stockier body. Both species reach about 3 centimetres (1.2 in) SL

Fish measurement

Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...

.

N. sternoptychum differs from N. spectabile in head shape, pectoral fin length, and some meristic

Meristics

Meristics is an area of ichthyology which relates to counting quantitative features of fish, such as the number of fins or scales. A meristic can be used to describe a particular species of fish, or used to identify an unknown species...

 features.

Males have an elongate genital papilla and enlarged pelvic fin odontode

Odontode

Odontodes, or dermal teeth, are hard structures found on the external surfaces of animals or near internal openings. They comprise a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel, a structure similar to that of teeth. They generally do not have the same...

s. Also, there is a patch of odontodes involving four paired plates on either side of the pre-anal shield between the pelvic fin origin and the anus, possibly involved in increased adhesion in mating encounters.