Glanapteryginae is a subfamily 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...

 Trichomycteridae

Trichomycteridae

Trichomycteridae is a family of catfishes commonly known as the pencil or parasitic catfishes. This family includes the infamous candiru fish, feared by some people for its alleged habit of entering into the urethra of humans....

. It includes four genera

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...

, Glanapteryx

Glanapteryx

Glanapteryx is a genus of catfishes of the family Trichomycteridae. It includes two species, G. anguilla and G. niobium....

, Listrura, Pygidianops

Pygidianops

Pygidianops is a genus of catfishes of the family Trichomycteridae. It includes three species, P. cuao, P. eigenmanni, and P. magoi.-Distribution:...

, and Typhlobelus

Typhlobelus

Typhlobelus is a genus of catfishes of the family Trichomycteridae. It includes four species, T. guacamaya, T. lundbergi, T. macromycterus, and T. ternetzi.-Distribution:...

.

Phylogeny

Monophyly

Monophyly

In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...

 of the subfamily is supported by five synapomorphies

Synapomorphy

In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...

 involving reductions in the fins, caudal skeleton, and laterosensory system

Lateral line

The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...

. It has been proposed that the sister-group to this subfamily is the Sarcoglanidinae

Sarcoglanidinae

Sarcoglanidinae is a subfamily of catfishes of the family Trichomycteridae. It includes six genera, Ammoglanis, Malacoglanis, Microcambeva, Sarcoglanis, Stauroglanis, and Stenolicmus.-Taxonomy:...

. Listrura is the 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...

 to the remainder of the subfamily. Glanapteryx is sister to a clade formed by the sister taxa Pygidianops and Typhlobelus.

Distribution

Glanapteryx, Pygidianops, and Typhlobelus are distributed in the Orinoco

Orinoco

The Orinoco is one of the longest rivers in South America at . Its drainage basin, sometimes called the Orinoquia, covers , with 76.3% of it in Venezuela and the remainder in Colombia...

 and 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...

. Listrura species are from Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, outside of the Amazon River basin. However, the distribution of glanapterygines may be greater than previously thought.

Description

Most of the subfamily is constituted by miniaturized species. Though miniaturized fish usually refers to fish that do not reach 25.4 millimetres (1.0 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:...

, Glanapteryx and Typhlobelus have been considered elongate miniatures due to their paedomorphic features and small head sizes, despite their lengths exceeding 25.4 mm.

Pygidianops and Typhlobelus are the most modified glanapterygines sharing extreme reduction or loss of pigmentation, fins, laterosensory system, and eyes; they are also miniaturized, yet retain the well-ossified

Ossification

Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

 skeleton comparable in both bone differentiation and degree of calcification to that observed in larger trichomycterids. All four of these genera are currently monophyletic.

Habitat

Glanapterygine phylogeny indicates that the evolution of the group followed a trend of decreasing dependence on leaf litter and increasing association with sand. Listrura occur in shallow-water leaf-litter deposits underlain by mud or deeper layers of leaf litter. Little is known about the habitats of the species of Glanapteryx, but information available indicates that they have been collected in association with leaf litter underlain with sand. By contrast, Pygidianops and Typhlobelus are entirely disassociated from leaf litter, and occupy exclusively clear loose sand; some species have been found to live exclusively in the substratum of the sand (rather than on the sand surface or in the water column above the sand), which could be the first vertebrates identified to be part of the meiofauna of benthic organisms. The latter two genera are more specialized for this lifestyle than any other catfishes, as evidenced by their loss of morphological traits. These two species also have paired keels called metapleural keels; these keels, formed by long ridges of stiffened integument, extend along the entire ventral margin of the abdomen, ending posteriorly shortly posterior to the anus. These keels probably serve to stabilize the body while moving in sand.