Cheirocerus is a 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

In human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...

 Pimelodidae

Pimelodidae

Pimelodidae, commonly known as the long-whiskered catfishes, is a family of catfishes .-Taxonomy:Pimelodidae has undergone much revision. Currently, the family contains about 30 genera and about 90 recognized and known but unnamed species...

. It includes three species, C. abuelo, C. eques, and C. goeldii.

Distribution and habitat

Cheirocerus is distributed throughout much of the Amazon River

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...

 basin, and appear to be absent from the Orinoco River. C. abuelo occurs in the Lake Maracaibo

Lake Maracaibo

Lake Maracaibo is a large brackish bay in Venezuela at . It is connected to the Gulf of Venezuela by Tablazo Strait at the northern end, and fed by numerous rivers, the largest being the Catatumbo. It is commonly considered a lake rather than a bay or lagoon, and at 13,210 km² it would be the...

 basin, C. eques in the Amazon River basin, and C. goeldii in the Purus River basin.

C. goeldii is more typical of lowland large rivers where the water may be warmer and deeper, though it may also occur far upstream. C. eques appears to occur closer to Andean

Andes

The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

 foothills where rivers may be cooler and shallower.

Description

Species of Cheirocerus have a fully ventral mouth with relatively fleshy lips, a broad premaxilla

Premaxilla

The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

, a crimped gas bladder

Gas bladder

The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth without having to waste energy in swimming...

 that appears to have fringe or finger-like projections, and the slender hollow tube extensions on each side of the gas bladder. These fish have an undeveloped dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 locking mechanism and no dorsal fin spine. They also have a relatively long adipose fin. These species all have three pairs of barbels

Barbel (anatomy)

A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...

. C. eques and C. goeldii display some geographic variations in certain morphometric

Morphometrics

Morphometrics refers to the quantitative analysis of form, a concept that encompasses size and shape. Morphometric analyses are commonly performed on organisms, and are useful in analyzing their fossil record, the impact of mutations on shape, developmental changes in form, covariances between...

 characteristics.

C. abuelo has a dusky-gray body colouration that varies from relatively plain to having numerous small brown spots, and usually has a broad, diffuse band crossing the nape

Nape

The nape is the back of the neck. In technical anatomical/medical terminology, the nape is referred to by the word nucha, which also gives the adjective corresponding to "nape" in English, "nuchal"....

 at the dorsal fin origin. Both C. goeldii and C. eques have a relatively uniform body colouration without spots; C. goeldii has a small, triangular spot at the dorsal fin origin, while C. eques has a distinct dark band at the dorsal fin origin.

C. abuelo appears to attain the largest size of the three species, reaching at least 22 centimetres (9 in). By contrast, the largest known C. eques is about 14 cm (5.5 in) and the largest C. goeldii is about 15 cm (6 in)

Ecology

Cheirocerus species are generally nocturnal. This is evidenced by the specialized gas bladder, hypothesized to enhance hearing, and the poorly developed pigmentation.

Diet mostly consists of benthic

Benthic zone

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such...

 invertebrates, with chironomid

Chironomidae

Chironomidae are a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae...

 larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e being a dominant component, but also including ostracod

Ostracod

Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....

s and mayfly

Mayfly

Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...

 nymph

Nymph (biology)

In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...

s.