Galeus
Encyclopedia
Galeus 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 catshark
Catshark
Catsharks are ground sharks of the family Scyliorhinidae, with over 150 known species. While they are generally known as catsharks, many species are commonly called dogfish....

, 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...

 Scyliorhinidae, commonly known as sawtail catsharks in reference to a distinctive saw-toothed crest of enlarged dermal denticles found along the upper edges of their caudal fins. They are found in the Atlantic, the western and central Pacific, and the Gulf of California
Gulf of California
The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland...

, inhabiting deep water on or close to the bottom. Members of this genus are rather small, slim sharks with firm bodies and thick, rough skin. Their heads are usually fairly long and pointed, and have large mouths with well-developed furrows at the corners. They have large pectoral and anal fins, and two similar 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...

s placed well back. Many species are ornately patterned with dark saddles and/or blotches. Sawtail catsharks feed on various invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

es, and may be either egg-laying or live-bearing. These harmless sharks are sometimes caught as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

 but are of minimal commercial value.

Taxonomy

Galeus, derived 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;...

 galeos meaning "shark", is one of the oldest carcharhiniform
Carcharhiniformes
The ground sharks, order Carcharhiniformes, are the largest order of sharks. With over 270 species, carcharhiniforms include a number of common types, such as the blue shark, catsharks, swellsharks, and sandbar shark....

 generic names. It was first used in a binomial
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...

 by Constantine Samuel Rafinesque in his 1810 Caratteri di alcuni nuovi generi e nuove specie di animali (principalmente di pesci) e piante della Sicilia: con varie osservazioni sopra i medesimi. Rafinesque listed G. melastomus, G. vulpecula (=Alopias vulpinus), G. mustelus (=Mustelus mustelus), and G. catulus (=Scyliorhinus canicula). Subsequently, in 1816 Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...

 used Galeus to refer to the genus presently known as Galeorhinus, and in 1818 William Elford Leach
William Elford Leach
William Elford Leach FRS was an English zoologist and marine biologist.Leach was born at Hoe Gate, Plymouth, the son of a solicitor. At the age of twelve he went to school in Exeter, studying anatomy and chemistry. By this time he was already collecting marine samples from Plymouth Sound and along...

 used Galeus to refer to genus presently known as Mustelus. As a result, 19th century authors generally used Galeus for the tope sharks, and Pristiurus, coined by Charles Lucien Bonaparte
Charles Lucien Bonaparte
Charles Lucien Jules Laurent Bonaparte, 2nd Prince of Canino and Musignano was a French naturalist and ornithologist.-Biography:...

 in 1834, for the sawtail catsharks.

Rafinesque likely intended G. mustelus to be the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 for Galeus, but of his listed species he furnished a description only for G. melastomus. Therefore, in 1908 Henry Weed Fowler
Henry Weed Fowler
Henry Weed Fowler was an American zoologist born in Holmesburg, Pennsylvania.He studied at Stanford University under David Starr Jordan...

 designated G. melastomus as the type species of Galeus, establishing the genus to contain the sawtail catsharks. Pristiurus became a junior synonym, though it continued to appear in scientific literature for some time after. Fowler's definition of Galeus gained widespread acceptance after Henry Bryant Bigelow
Henry Bryant Bigelow
Henry Bryant Bigelow was an American oceanographer and marine biologist.After graduating from Harvard in 1901, he began working with famed ichthyologist Alexander Agassiz. Bigelow accompanied Agassiz on several major marine science expeditions including one aboard the Albatross in 1907...

 and William Charles Schroeder
William Charles Schroeder
William Charles Schroeder was an American ichthyologist. He was born on Staten Island, New York. He, along with his lifelong colleague Henry Bryant Bigelow, made substantial contributions to the knowledge of the fish fauna of the western North Atlantic...

's 1948 taxonomic review. In 1952, Philip Orkin advocated that Pristiurus take precedence over Galeus, based on David Starr Jordan
David Starr Jordan
David Starr Jordan, Ph.D., LL.D. was a leading eugenicist, ichthyologist, educator and peace activist. He was president of Indiana University and Stanford University.-Early life and education:...

 and Barton Warren Evermann
Barton Warren Evermann
Barton Warren Evermann was an American ichthyologist. He was born in Monroe County, Iowa, and graduated from Indiana University in 1886. For 10 years, he served as teacher and superintendent of schools in Indiana and California. He was professor of biology at the Indiana State University in...

's (possibly questionable) designation of G. mustelus as a type species for Galeus in 1896. Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...

 and most other recent authors have not upheld his proposal, in the interests of taxonomic stability.

Phylogeny and evolution

Most taxonomic studies have concluded the closest relatives of Galeus to be Apristurus
Apristurus
Apristurus is a genus of catshark, the family Scyliorhinidae, commonly known as the ghost or demon catsharks.-Species:* Apristurus albisoma Nakaya & Séret, 1999* Apristurus ampliceps Sasahara, Sato & Nakaya, 2008...

, Asymbolus
Asymbolus
Asymbolus is a genus of catshark in the family Scyliorhinidae.-Species:* Asymbolus analis * Asymbolus funebris Compagno, Stevens & Last, 1999...

, Parmaturus
Parmaturus
Parmaturus is a genus of catshark in the family Scyliorhinidae.-Species:* Parmaturus albimarginatus Séret & Last, 2007 * Parmaturus albipenis Séret & Last, 2007...

, and/or Cephalurus. Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...

 has placed Galeus with Apristurus, Bythaelurus
Bythaelurus
Bythaelurus is a genus of catshark in the Scyliorhinidae family.-Species:* Bythaelurus alcockii * Bythaelurus canescens...

, Cephalurus, Parmaturus, and Pentanchus in the tribe Pentanchini of the subfamily Pentanchinae, based on morphological characters
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

. Galeus was suggested to be the sister group of Apristurus in a 2005 phylogenetic study based on mitochondrial
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...

 and nuclear DNA
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...

 gene sequences, by Samuel Iglésias and colleagues. The affinity between Galeus and Apristurus was also upheld, albeit weakly, in a 2006 phylogenetic analysis based on three mitochondrial DNA genes, by Brett Human and colleagues. Within the genus, though the G. arae species complex
Species complex
A species complex is a group of closely related species, where the exact demarcation between species is often unclear or cryptic owing to their recent and usually still incomplete reproductive isolation. Ring species, superspecies and cryptic species complex are example of species complex...

, G. atlanticus, G. eastmani, G. melastomus, G. piperatus, G. polli, and G. sauteri definitely form a monophyletic group, the assignment of other species (e.g. G. murinus) within the genus is more problematic. In the aforementioned study by Iglésias and colleagues, which included five Galeus species, G. eastmani, G. gracilis
Slender sawtail catshark
The slender sawtail catshark is a little-known species of catshark, family Scyliorhinidae, endemic to northern Australia. It is found over the continental slope in on water...

, and G. sauteri were grouped into one clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 and G. melastomus and G. murinus grouped into another. Galeus fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s, dating to the Burdigalian
Burdigalian
The Burdigalian is, in the geologic timescale, an age or stage in the early Miocene. It spans the time between 20.43 ± 0.05 Ma and 15.97 ± 0.05 Ma...

 (20.43–15.97 Ma) and Langhian
Langhian
The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene epoch/series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma . The Langhian was a continuing warming period defined by Lorenzo Pareto in 1864, it was originally established in the Langhe area north...

 (15.97–13.65 Ma) stages of the early Miocene
Early Miocene
The Early Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages....

, have been recovered from France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

.

Distribution and habitat

The centers of biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 for Galeus are the North Atlantic (8 species) and the northwestern Pacific (4 species). A few outlying species are found in the South Atlantic (G. mincaronei and G. polli), Oceania
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...

 (G. gracilis and G. priapus), and the Gulf of California
Gulf of California
The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland...

 (G. piperatus). In the western Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

, this genus appears to be replaced by the ecologically similar genus Holohalaelurus
Holohalaelurus
Holohalaelurus is a genus of catshark in the family Scyliorhinidae, commonly known as Izak catsharks or hallelujah sharks.-Species:* Holohalaelurus favus Human, 2006...

. Sawtail catsharks are demersal in habits and occur in deep water over outer continental and insular shelves
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

 and upper slopes.

Description

Sawtail catsharks reach maximum lengths of between 25 and 90 cm (9.8 and 35.4 in). They have slender, firm bodies and narrow, slightly flattened heads with short to long, pointed snouts. The nostrils are divided into incurrent and excurrent openings by triangular flaps of skin on their anterior rims. The horizontally oval eyes are placed mostly on the sides of the head and equipped with rudimentary nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...

s (protective third eyelids); below each eye is a subtle ridge, and behind is a small spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

 (auxiliary respiratory
Aquatic respiration
Aquatic respiration is the process whereby an aquatic animal obtains oxygen from water.-Fish:In most fish respiration takes place through gills. Lungfish, however, possess one or two lungs...

 opening). The mouth is rather large and wide, and when closed the upper teeth are exposed. There are short to long furrows around the corners of the jaws. The teeth are small and number 47–78 rows in the upper jaw and 48–82 rows in the lower jaw; each tooth has a narrow central cusp flanked by one or more smaller cusplets on either side. There are five pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...

s.
The two 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...

s are nearly equal in size and shape, and are placed well back on the body, behind the origins of the pelvic fins. The pectoral fins are fairly large and broad, with angular to rounded corners. The pelvic fins are much smaller, and bear claspers in males; in G. murinus and G. nipponensis, the pelvic fin inner margins are partially fused to form an "apron" over the base of the claspers. The anal fin is elongated and much larger than the pelvic and dorsal fins; its position relative to the pelvic and caudal fins varies from very close to well-spaced. The caudal peduncle can be nearly cylindrical to laterally compressed, depending on species. The caudal fin comprises more or less a quarter of the total length, and is low with a small lower lobe and a ventral notch near the tip of the upper lobe.

The skin is thick and densely covered by small, overlapping, well-calcified
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...

 dermal denticles; each denticle has a leaf-shaped crown with a horizontal ridge and three teeth on the posterior margin. There is a prominent, saw-like crest of enlarged denticles along the dorsal margin of the caudal fin. G. murinus and G. springeri also have a similar crest along the ventral margin of the caudal fin. Galeus species are typically grayish or brownish above and lighter below, and most have a pattern of darker saddles and/or blotches along the back and tail. The interior of the mouth may be light or dark.

Biology and ecology

Natural history data is scant for most Galeus species. They feed on various types of invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

es on or near the bottom. In Suruga Bay
Suruga Bay
Suruga Bay is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of an imaginary line joining Omaezaki Point and Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honshū to the southwest and west and the Izu Peninsula to the east.-Geology:Suruga...

, the dietary compositions of G. eastmani and juvenile G. nipponensis differ significantly, suggesting there is reduced interspecific competition
Interspecific competition
Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resource in an ecosystem...

 between co-occurring Galeus species. Reproductive modes within the genus are notably diverse: while most species are oviparous and lay encapsulated eggs on the sea floor, there is a single aplacental viviparous species (G. polli) that retains eggs internally and gives live birth. Among the oviparous species, most (e.g. G. murinus, G. nipponensis) exhibit single oviparity, in which only a single egg matures within each of the female's oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...

s at a time. In contrast, a few species such as G. atlanticus and G. melastomus exhibit multiple oviparity, in which several eggs can mature within each oviduct simultaneously. Single oviparity is considered to be the 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:...

 condition, while multiple oviparity and aplacental viviparity are thought to be more derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...

.

Human interactions

Sawtail catsharks pose no danger to humans and have little economic value, though varying numbers are caught incidentally
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

 by deepwater commercial fisheries. Some of the larger species, such as G. melastomus and G. polli, are occasionally utilized for meat, fishmeal, and/or leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...

. The International Union for Conservation of Nature (IUCN) has listed G. atlanticus and G. mincaronei, both of which have very restricted distributions, as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...

 and Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...

respectively.
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