Magosternarchus
Encyclopedia
Magosternarchus is a genus
of weakly electric knifefish
in the family Apteronotidae, containing two species
. They are native to Brazil
, occurring in large river
channels in the Amazon River basin. Both species are unusual benthic predators that specialize in biting off the tails of other knifefishes, and are characterized by their greatly enlarged jaws and teeth.
, who has made many contributions to the study of gymnotiform knifefishes; the latter part of the name sternarchus is from the Greek
sternon ("chest") and archos ("rectum"), referring to the forward placement of the urogenital opening
in this group of fishes. The species name of M. raptor is from the Latin
for "plunderer", referring to its tail-eating habits; the species name of M. duccis refers to the Duke University
Center for Creative Ichthyology (DUCCIS), an ichthyology
club. Based on several shared skeletal traits, the closest relative of Magnosternarchus is believed to be the genus Sternarchella.
system, including in the Rio Negro to at least above the confluence of the Rio Blanco
. M. raptor has been collected as far upstream as the lower Rio Jutai and as far downstream to the lower Rio Xingu; M. ducci has been collected as far upstream as Rio Ica and as far downstream as Rio Trombetas. They are found in large, swift-flowing whitewater
and blackwater river
channels, at least 10 m (32.8 ft) from shore, at depths of 1 –. They are absent from beach
es, small stream
s, and other marginal habitat
s.
s, allowing for a wide gape, and their numerous, large, conical teeth. Both the premaxilla
and the dentary bone are elongated, the former bearing two to three rows of teeth (numbering 9–14 in the outermost row) and the latter bearing three rows of teeth (numbering 15–19 in the outermost row). The deeply concave dorsal margin of the opercle also serves to distinguish this genus. The eye
s are small and placed towards the top of the head. The body is similar to other ghost knifefish
es, being laterally compressed with a long anal fin, a small caudal fin, and no dorsal
or pelvic fins. There is a dorsal filament originating posterior to the midpoint of the body.
The coloration is pinkish-white to translucent, with varying numbers of grayish-brown to black chromatophore
s on the upper sides of the body. The chromatophores are most concentrated at the dorsal midline, with the dorsal filament usually the darkest, and there are also thin, vertical lines of chromatophores on the connective tissue
between the anal fin radial muscle
s. The pigmentation on the nape
is interrupted by a pair of pale, comma-shaped lateralis tubes. Tiny light dots of electrosensory
cell cluster
s are present over the back. The anal fin is clear, the caudal fin is clear to dusky, and the anal fin is clear in front and darkly pigment
ed along the base in the back.
contents of Magnosternarchus specimens have been the tails of other gymnotiform knifefish
es. Most of the Magnosternarchus specimens thus far examined have also possessed regenerated
tails. Like other apteronid knifefishes, Magnosternarchus is capable of producing a continuous weak electrical discharge for electrolocation and electrocommunication
.
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 weakly electric knifefish
Gymnotiformes
The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
in the family Apteronotidae, containing two species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. They are native to 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...
, occurring in large river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
channels in the Amazon River basin. Both species are unusual benthic predators that specialize in biting off the tails of other knifefishes, and are characterized by their greatly enlarged jaws and teeth.
Taxonomy
The name Magosternarchus honors Dr. Francisco Mago LecciaFrancisco Mago Leccia
Francisco Mago Leccia born in Tumeremo Bolívar State – Venezuela on May 21, 1931. Death in Caracas - Venezuela in March 2004. Mago is distinguished Venezuelan ichthyologist specialized in electric fish of rivers and lagoon of Venezuela and South America...
, who has made many contributions to the study of gymnotiform knifefishes; the latter part of the name sternarchus is from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
sternon ("chest") and archos ("rectum"), referring to the forward placement of the urogenital opening
Urogenital opening
The urogenital opening is where waste products of the body and reproductive fluids are expelled to the environment outside of the body cavity. In some organisms, including birds and many fish, discharge from the urological, digestive, and reproductive systems empty into a common sac called the...
in this group of fishes. The species name of M. raptor is from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "plunderer", referring to its tail-eating habits; the species name of M. duccis refers to the Duke University
Duke University
Duke University is a private research university located in Durham, North Carolina, United States. Founded by Methodists and Quakers in the present day town of Trinity in 1838, the school moved to Durham in 1892. In 1924, tobacco industrialist James B...
Center for Creative Ichthyology (DUCCIS), an ichthyology
Ichthyology
Ichthyology is the branch of zoology devoted to the study of fish. This includes skeletal fish , cartilaginous fish , and jawless fish...
club. Based on several shared skeletal traits, the closest relative of Magnosternarchus is believed to be the genus Sternarchella.
Distribution and habitat
Both species of Magnosternarchus are believed to range widely in the Amazon RiverAmazon 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...
system, including in the Rio Negro to at least above the confluence of the Rio Blanco
Río Blanco
-United States:*Rio Blanco & Rio Blanco County, Colorado**Rio Blanco Oil Shale Company*Rio Blanco, Puerto Rico*Blanco River -Uruguay:...
. M. raptor has been collected as far upstream as the lower Rio Jutai and as far downstream to the lower Rio Xingu; M. ducci has been collected as far upstream as Rio Ica and as far downstream as Rio Trombetas. They are found in large, swift-flowing whitewater
Whitewater
Whitewater is formed in a rapid, when a river's gradient increases enough to disturb its laminar flow and create turbulence, i.e. form a bubbly, or aerated and unstable current; the frothy water appears white...
and blackwater river
Blackwater river
A blackwater river is a river with a deep, slow-moving channel that flows through forested swamps and wetlands. As vegetation decays in the water, tannins are leached out, resulting in transparent, acidic water that is darkly stained, resembling tea or coffee. Most major blackwater rivers are in...
channels, at least 10 m (32.8 ft) from shore, at depths of 1 –. They are absent from beach
Beach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
es, small stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s, and other marginal habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s.
Description
Magosternarchus species are immediately recognizable by their large jawJaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
s, allowing for a wide gape, and their numerous, large, conical teeth. Both the 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....
and the dentary bone are elongated, the former bearing two to three rows of teeth (numbering 9–14 in the outermost row) and the latter bearing three rows of teeth (numbering 15–19 in the outermost row). The deeply concave dorsal margin of the opercle also serves to distinguish this genus. The eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
s are small and placed towards the top of the head. The body is similar to other ghost knifefish
Ghost knifefish
The ghost knifefishes are a family, Apteronotidae, of ray-finned fishes in the order Gymnotiformes. These fish can be found in the freshwater of Panama and South America....
es, being laterally compressed with a long anal fin, a small caudal fin, and no dorsal
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...
or pelvic fins. There is a dorsal filament originating posterior to the midpoint of the body.
The coloration is pinkish-white to translucent, with varying numbers of grayish-brown to black chromatophore
Chromatophore
Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...
s on the upper sides of the body. The chromatophores are most concentrated at the dorsal midline, with the dorsal filament usually the darkest, and there are also thin, vertical lines of chromatophores on the connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
between the anal fin radial muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s. The pigmentation on 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"....
is interrupted by a pair of pale, comma-shaped lateralis tubes. Tiny light dots of electrosensory
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
cell cluster
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s are present over the back. The anal fin is clear, the caudal fin is clear to dusky, and the anal fin is clear in front and darkly pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
ed along the base in the back.
Biology and ecology
The only identifiable stomachStomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
contents of Magnosternarchus specimens have been the tails of other gymnotiform knifefish
Gymnotiformes
The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
es. Most of the Magnosternarchus specimens thus far examined have also possessed regenerated
Regeneration (biology)
In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organs, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. At its most...
tails. Like other apteronid knifefishes, Magnosternarchus is capable of producing a continuous weak electrical discharge for electrolocation and electrocommunication
Animal communication
Animal communication is any behavior on the part of one animal that has an effect on the current or future behaviour of another animal. The study of animal communication, is sometimes called Zoosemiotics has played an important part in the...
.
Species
- Magnosternarchus duccis Lundberg, Coz Fernandes & Albert 1996 This species differs from M. raptor in having a markedly projecting lower jaw that often extends past and over the upper jaw and snout. The head is elongated and deep, with a concave dorsal profile. There are 204–212 fin rays in the anal fin, 14–16 rays in the pectoral fins, and 15 rays in a pointed caudal fin. The maximum reported length is 22.6 cm (8.9 in).
- Magnosternarchus raptor Lundberg, Coz Fernandes & Albert 1996 This species has an elongated, deep head with a moderately elongated, conical snout. The jaws are of equal length or the upper jaw is slightly longer. There are 180–197 fin rays in the anal fin, 14–16 rays in the pectoral fins, and 17 rays in a rounded caudal fin. The maximum reported length is 19.9 cm (7.8 in).