Lacantunia enigmatica
Encyclopedia
The Chiapas catfish, Lacantunia enigmatica, is an unusual species 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...

 (Order Siluriformes) newly described in 2005 from the Lacantún River
Lacantún River
-References:*Atlas of Mexico, 1975 .*The Prentice Hall American World Atlas, 1984.*Rand McNally, The New International Atlas, 1993....

 in the Mexican
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 state of Chiapas
Chiapas
Chiapas officially Estado Libre y Soberano de Chiapas is one of the 31 states that, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 118 municipalities and its capital city is Tuxtla Gutierrez. Other important cites in Chiapas include San Cristóbal de las...

. While discovery of an undescribed species of catfish is not uncommon, discovery of a new family-level taxon of any vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

 group is a rare event. The Chiapas catfish mainly feeds on crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s, prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...

s, small fish, and large, tough plant seeds. This catfish is commonly fished in its natural habitat, where it is known as madre de juil, which means "mother of Rhamdia
Rhamdia
Rhamdia is a genus of catfishes of the family Heptapteridae.The monophyly of Rhamdia is not yet established.Rhamdia catfishes are nocturnal, opportunistic carnivores. This genus includes a number of troglobitic members, encompassing a number of taxa, including R. quelen urichi, R. laticauda...

" (a common fish in the area).

Discovery

It first came to the attention of scientists in 1996 when Rócio Rodiles-Hernández, a Mexican ichthyologist conducting a biotic survey on the river, collected the first specimens from the Chiapas-Guatemala
Guatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...

 border. Unable to identify the species, Rodiles involved two American catfish specialists, Dean A. Hendrickson of the University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...

 and John G. Lundberg of the Academy of Natural Sciences
Academy of Natural Sciences
The Academy of Natural Sciences of Drexel University, formerly Academy of Natural Sciences of Philadelphia, is the oldest natural science research institution and museum in the New World...

 of Philadlephia. A detailed comparative morphological study employing high resolution, three-dimensional CT-scan imagery of the fish's anatomy revealed a number of distinctive characteristics unique to this species and the absence of characters needed to place this fish in any existing catfish family. In a 2005 publication these three ichthyologists with Julian M. Humphries of the University of Texas described this fish as a new species, genus and family of catfish.

Taxonomy

This fish is not related to any of the families found in its range (Ariidae
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...

, Ictaluridae
Ictaluridae
The Ictaluridae, sometimes called Ictalurids, are a family of catfish native to North America, where they are important food fish and sometimes as a sport fish. They include fish commonly known as bullheads, madtoms, channel catfish, and blue catfish....

, Heptapteridae
Heptapteridae
Heptapteridae is a family of catfish that originate from Mexico to South America. Heptapteridae is derived from Greek, hepta meaning seven and pteron meaning fin....

). It is most similar to Ictaluridae, but lacks some important characteristics to classify this fish into this family or the other two families. Initial study has placed this fish above Diplomystidae, Cetopsidae
Cetopsidae
Cetopsidae is a small family of catfishes , commonly called the whale catfishes.-Taxonomy:This family contains five genera. It is divided into two subfamilies, Cetopsinae and Helogeneinae. Helogeneinae was previously a family-level group, but now it has been reclassified as a subfamily of Cetopsidae...

, and Hypsidoridae, but further classification is unknown. It is probable that this family represents a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 group in which intermediates have disappeared.

With recent molecular evidence, it has been shown that Lacantunia 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 Claroteidae
Claroteidae
The Claroteidae are a family of catfish found in Africa. This family was separated from Bagridae. However, the monophyly of the family is sometimes contested....

, an Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

n catfish family. It probably diverged from the claroteids in the Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 between 75 to 90 mya.

Distribution and habitat

The generic name of the fish reflects its distribution in the Río Lacantún
Lacantún River
-References:*Atlas of Mexico, 1975 .*The Prentice Hall American World Atlas, 1984.*Rand McNally, The New International Atlas, 1993....

 drainage, flowing through the Montes Azules and Selva Lacandona Biosphere Reserves in México into that country’s largest river, the Río Usumacinta
Usumacinta River
The Usumacinta River is a river in southeastern Mexico and northwestern Guatemala. It is formed by the junction of the Pasión River, which arises in the Sierra de Santa Cruz and the Salinas River, also known as the Chixoy, or the Negro, which descends from the Sierra Madre de Guatemala...

. Its known distribution does not extend beyond a small area in the Lacantún and Lacanjún rivers of central Chiapas. Lacantunia has never been collected in the large Usumacinta River into which these smaller rivers flow. With the description of the new family, there are four catfish families found in this region

These fish inhabit deep river channels and pools with rocks and strong eddy currents. Few specimens were taken in stream mouths.

Physical characteristics

Key variations that differentiate this genus from all other families are the shape of the animal's skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

, jaw muscles, 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...

 — which fish use to rise and sink in water. The gas bladder has paired diverticulae
Diverticulum
A diverticulum is medical or biological term for an outpouching of a hollow structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false....

, while other catfish families either have no diverticulae or singular diverticulae. Some external characteristics that may help distinguish this fish include nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...

s set far apart, the presences of nasal barbels, maxillary barbels placed above the lip distantly from the corner of the mouth, and a rounded caudal fin. This fish has four pairs of barbels. The maximum length of fish ish of this species exceed 40 centimetres (16 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:...

. It is depressed (flattened) near the head and compressed (thin) near the tail. The head is blunt and rounded, and the mouth is usually not subterminal (down-turned). The adipose fin is large and thick. This fish has dorsal and pectoral fin spines.

External links

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