Round ray
Encyclopedia
Urolophidae is a family
of rays
in the order Myliobatiformes
, commonly known as stingarees or round stingrays; this family formerly included the genera Urobatis and Urotrygon of the Americas
, which are presently recognized as forming their own family Urotrygonidae
. Stingarees are found in the Indo-Pacific
region, with the greatest diversity
off Australia
. They are sluggish, bottom-dwelling fish that have been recorded from shallow waters close to shore to deep waters over the upper continental slope. Measuring between 15–80 cm (5.9–31.5 in) long, these rays have oval to diamond-shaped pectoral fin discs and relatively short tails that terminate in leaf-shaped caudal fins, and may also have small dorsal fin
s and lateral skin folds. Most are smooth-skinned, and some have ornate dorsal color patterns.
Stingarees feed on or near the sea floor, consuming small invertebrate
s and occasionally bony fishes. They are aplacental viviparous, meaning that the embryo
s emerge from eggs inside the uterus
, and are sustained to term first by yolk and later by maternally produced histotroph ("uterine milk"). As far is known, the gestation period
lasts around a year and litter sizes tend to be small. Stingarees have one or two relatively large, venom
ous stinging spines on their tail for defense, with which they can inflict a painful wound on humans. Generally, stingarees have no economic value. Some species form a substantial component of the bycatch
of commercial trawl fisheries
.
and Jakob Henle
created the genus Urolophus in 1837; in their subsequent 1838–41 Systematische Beschreibung der Plagiostomen, the pair created the genus Trygonoptera and also made the first reference to the urolophids as a group. The family has traditionally also included the genera Urobatis and Urotrygon of the Americas
; John McEachran, Katherine Dunn, and Tsutomu Miyake moved them to their own family, Urotrygonidae
, in 1996.
Recent phylogenetic analyses have confirmed that the urolophids and related taxa
belong to the order Myliobatiformes; they were once placed in the order Rajiformes
with the guitarfish
es and skate
s. Based on morphological characters
, John McEachran and Neil Aschliman determined in a 2004 study that the urolophids formed a clade
with the giant stingaree (Plesiobatis daviesi), and that the two were basal
to a clade
containing all other myliobatiform families except Platyrhinidae
, Hexatrygonidae, and Zanobatidae. They proposed including Plesiobatis in the family Urolophidae, and classifying the family within the superfamily
Urolophoidea within Myliobatiformes.
T. testacea. It has often been considered synonymous with Urolophus, but this has been refuted by recent studies. Trygonoptera can be distinguished from Urolophus in that the outer rims of its nostrils are enlarged into broad, flattened lobes; the two also differ in aspects of the skeleton
.
oura, meaning "tail", and lophos, meaning "crest". In Urolophus, the outer rims of the nostrils are not enlarged into lobes, but may form a small knob at the back. Raia (Leiobatus) Blainville, 1816 is a synonym of Urolophus; though his account was published earlier, none of species Blainville listed for Leiobatus had descriptions, thus rendering them invalid. Urolophus fossil
s have been recovered dating back to the Eocene
epoch
(c. 56–34 Ma).
for stingarees is Australia
, where all 6 Trygonoptera and 15 of the 22 Urolophus species are endemic. A number of species are also found in the Coral Sea
, a few in the Malay Archipelago
, and one (the sepia stingray
, Urolophus aurantiacus) in the northwestern Pacific. Stingarees are bottom-dwelling rays that can be found from very shallow, inshore habitat
s such as estuaries and bay
s, to a depth of 420 m (1,378 ft) well offshore on the upper continental shelf
. Some are extremely common; one study in the coastal waters of southwestern Australia found that the four most abundant stingaree species constituted over 17% of the biomass
of benthic fishes.
in shape. The snout is usually short and does not protrude much from the disc. The eyes are placed atop the disc and usually fairly large; immediately posterior are teardrop-shaped spiracle
s (auxiliary respiratory
openings). There is a curtain of skin between the nostrils, formed from the fusion of the anterior nasal flaps, that reaches the mouth. There are varying numbers of papillae (nipple-like structures) on the floor of the mouth and sometimes also on the outside of the lower jaw. The teeth in both jaws are small, with rhomboid bases and blunt to pointed crowns; they are arranged with a quincunx
pattern and number less than 50 rows in either jaw. The five pairs of gill slit
s are short and located beneath the disc.
The pelvic fins are small with rounded margins; claspers are found on males. The tail is shorter than to about equal to the disc, either flattened or thickly oval in cross-section, and ends in a leaf-shaped, symmetrical caudal fin. One or two relatively large, serrated stinging spines are placed atop the tail about halfway along its length. Some species have a small dorsal fin
immediately before the spine, and/or lateral skin folds running along either side of the tail. All species lack dermal denticles (except for the New Ireland stingaree
, Urolophus armatus). Stingarees are generally shades of yellow, green, brown or gray above and pale below; some species are plain, while others are adorned with spots, rings, blotches, lines, or more complex patterns.
. They are predators of small benthic and burrowing invertebrate
s such as crustacean
s and polychaete worms, and also occasionally small bony fishes. Studies have shown that stingarees that overlap in range differ in their diet composition, which likely serves to reduce competition. For example, off southwestern Australia the masked stingaree
(Trygonoptera personata) and western shovelnose stingaree (T. mucosa) feed mostly on different types of polychaetes, while the sparsely-spotted stingaree (Urolophus paucimaculatus) and lobed stingaree
(U. lobatus) feed mostly on different types of crustaceans.
Like other myliobatiforms, stingarees have an aplacental viviparous mode of reproduction in which the embryo
s hatch within the uterus
and are nourished first by yolk, and later by histotroph ("uterine milk") produced by the mother and likely delivered through specialized extensions of the uterine epithelium
called "trophonemata". For those species whose life histories have been investigated, the gestation period
lasts 10–12 months and the litter size is small, no more than one or two in some cases. The small litter is likely due to the relatively large size of stingaree pups, which measure around half the maximum size at birth.
ous stings. Species differ in temperament; the sparse-spotted stingaree (Urolophus paucimaculatus) is reportedly more aggressive, and the spotted stingaree (U. gigas) less so. When threatened, the crossback stingaree (U. cruciatus) raises its tail over its disc like a scorpion
. Some species of stingarees are regularly caught incidentally
in bottom trawls by commercial fisheries
. They are generally discarded due to their small size, though some may be processed into fishmeal. Stingarees caught from shallow water likely have relatively high chances of survival, but of concern is their tendency to abort any gestating young when captured and handled.
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...
of rays
Batoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
in the order Myliobatiformes
Myliobatiformes
Myliobatiformes is one of the four orders of batoids, cartilaginous fishes related to sharks. They were formerly included in the order Rajiformes, but more recent phylogenetic studies have shown that the myliobatiforms are a monophyletic group, and that its more derived members evolved their...
, commonly known as stingarees or round stingrays; this family formerly included the genera Urobatis and Urotrygon of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
, which are presently recognized as forming their own family Urotrygonidae
Urotrygonidae
Urotrygonidae is a family of rays in the order Myliobatiformes, commonly referred to as the American round stingrays or round rays. They are native to the tropical and warm temperate marine waters of the Americas. The two genera in this family were formerly placed within the family Urolophidae,...
. Stingarees are found in the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region, with the greatest diversity
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...
off Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. They are sluggish, bottom-dwelling fish that have been recorded from shallow waters close to shore to deep waters over the upper continental slope. Measuring between 15–80 cm (5.9–31.5 in) long, these rays have oval to diamond-shaped pectoral fin discs and relatively short tails that terminate in leaf-shaped caudal fins, and may also have small 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 and lateral skin folds. Most are smooth-skinned, and some have ornate dorsal color patterns.
Stingarees feed on or near the sea floor, consuming small 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 occasionally bony fishes. They are aplacental viviparous, meaning that the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s emerge from eggs inside the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
, and are sustained to term first by yolk and later by maternally produced histotroph ("uterine milk"). As far is known, the gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
lasts around a year and litter sizes tend to be small. Stingarees have one or two relatively large, venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous stinging spines on their tail for defense, with which they can inflict a painful wound on humans. Generally, stingarees have no economic value. Some species form a substantial component of the 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...
of commercial trawl fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
.
Taxonomy and phylogeny
German biologists Johannes MüllerJohannes Peter Müller
Johannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...
and Jakob Henle
Friedrich Gustav Jakob Henle
Friedrich Gustav Jakob Henle was a German physician, pathologist and anatomist. He is credited with the discovery of the loop of Henle in the kidney. His essay "On Miasma and Contagia" was an early argument for the germ theory of disease...
created the genus Urolophus in 1837; in their subsequent 1838–41 Systematische Beschreibung der Plagiostomen, the pair created the genus Trygonoptera and also made the first reference to the urolophids as a group. The family has traditionally also included the genera Urobatis and Urotrygon of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
; John McEachran, Katherine Dunn, and Tsutomu Miyake moved them to their own family, Urotrygonidae
Urotrygonidae
Urotrygonidae is a family of rays in the order Myliobatiformes, commonly referred to as the American round stingrays or round rays. They are native to the tropical and warm temperate marine waters of the Americas. The two genera in this family were formerly placed within the family Urolophidae,...
, in 1996.
Recent phylogenetic analyses have confirmed that the urolophids and related taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
belong to the order Myliobatiformes; they were once placed in the order Rajiformes
Rajiformes
Rajiformes is one of the four orders of batoids, flattened cartilaginous fishes related to sharks.Rajiforms are distinguished by the presence of greatly enlarged pectoral fins, which reach as far forward as the sides of the head, with a generally flattened body. The undulatory pectoral fin motion...
with the guitarfish
Guitarfish
The guitarfish are a family, Rhinobatidae, of rays. The guitarfish are known for an elongated body with a flattened head and trunk and small ray like wings. The combined range of the various species is tropical, subtropical and temperate waters worldwide. They often travel in large...
es and skate
Skate
Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....
s. 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....
, John McEachran and Neil Aschliman determined in a 2004 study that the urolophids formed a 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...
with the giant stingaree (Plesiobatis daviesi), and that the two were 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:...
to a 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...
containing all other myliobatiform families except Platyrhinidae
Platyrhinidae
Platyrhinidae is a family of rays in the order Myliobatiformes, commonly known as thornbacks due to their dorsal rows of large thorns. They resemble guitarfishes in shape, but are in fact more closely related to stingrays.-Genera and species:...
, Hexatrygonidae, and Zanobatidae. They proposed including Plesiobatis in the family Urolophidae, and classifying the family within the superfamily
Superfamily
The term superfamily is used to describe several different concepts in different scientific fields:* Superfamily and Superfamily : a level of biological classification; redirects to Taxonomic rank...
Urolophoidea within Myliobatiformes.
Trygonoptera
Müller and Henle defined Trygonoptera in 1841, along with the type speciesType 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...
T. testacea. It has often been considered synonymous with Urolophus, but this has been refuted by recent studies. Trygonoptera can be distinguished from Urolophus in that the outer rims of its nostrils are enlarged into broad, flattened lobes; the two also differ in aspects of the skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
.
Urolophus
Müller and Henle created Urolophus in an 1837 issue of Bericht Akademie der Wissenschaften zu Berlin; the type species is Raja cruciata (=U. cruciatus) Lacepède, 1804. The name is derived from the GreekGreek 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;...
oura, meaning "tail", and lophos, meaning "crest". In Urolophus, the outer rims of the nostrils are not enlarged into lobes, but may form a small knob at the back. Raia (Leiobatus) Blainville, 1816 is a synonym of Urolophus; though his account was published earlier, none of species Blainville listed for Leiobatus had descriptions, thus rendering them invalid. Urolophus fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been recovered dating back to the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
epoch
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
(c. 56–34 Ma).
Distribution and habitat
The center of biodiversityBiodiversity
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 stingarees is Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, where all 6 Trygonoptera and 15 of the 22 Urolophus species are endemic. A number of species are also found in the Coral Sea
Coral Sea
The Coral Sea is a marginal sea off the northeast coast of Australia. It is bounded in the west by the east coast of Queensland, thereby including the Great Barrier Reef, in the east by Vanuatu and by New Caledonia, and in the north approximately by the southern extremity of the Solomon Islands...
, a few in the Malay Archipelago
Malay Archipelago
The Malay Archipelago refers to the archipelago between mainland Southeastern Asia and Australia. The name was derived from the anachronistic concept of a Malay race....
, and one (the sepia stingray
Sepia stingray
The sepia stingray is a species of fish in the Urolophidae family. It is found in Japan, Taiwan, Vietnam, possibly North Korea, and possibly South Korea. It is threatened by habitat loss.-Source:...
, Urolophus aurantiacus) in the northwestern Pacific. Stingarees are bottom-dwelling rays that can be found from very shallow, inshore 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 such as estuaries and bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, to a depth of 420 m (1,378 ft) well offshore on the upper continental shelf
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,...
. Some are extremely common; one study in the coastal waters of southwestern Australia found that the four most abundant stingaree species constituted over 17% of the biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
of benthic fishes.
Description
Stingarees are modestly sized, ranging from 30 to 80 cm (11.8 to 31.5 in) long. They have greatly enlarged pectoral fins fused to the head, forming a disc that may be nearly circular, to oval, to rhomboidRhomboid
Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are oblique.A parallelogram with sides of equal length is a rhombus but not a rhomboid....
in shape. The snout is usually short and does not protrude much from the disc. The eyes are placed atop the disc and usually fairly large; immediately posterior are teardrop-shaped 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...
s (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...
openings). There is a curtain of skin between the nostrils, formed from the fusion of the anterior nasal flaps, that reaches the mouth. There are varying numbers of papillae (nipple-like structures) on the floor of the mouth and sometimes also on the outside of the lower jaw. The teeth in both jaws are small, with rhomboid bases and blunt to pointed crowns; they are arranged with a quincunx
Quincunx
A quincunx is a geometric pattern consisting of five points arranged in a cross, that is five coplanar points, four of them forming a square or rectangle and a fifth at its center...
pattern and number less than 50 rows in either jaw. The 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 are short and located beneath the disc.
The pelvic fins are small with rounded margins; claspers are found on males. The tail is shorter than to about equal to the disc, either flattened or thickly oval in cross-section, and ends in a leaf-shaped, symmetrical caudal fin. One or two relatively large, serrated stinging spines are placed atop the tail about halfway along its length. Some species have a small 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...
immediately before the spine, and/or lateral skin folds running along either side of the tail. All species lack dermal denticles (except for the New Ireland stingaree
New Ireland stingaree
The New Ireland stingaree is a species of stingray in the family Urolophidae, known only from a single juvenile male long, collected in the Bismarck Archipelago. This species has an oval pectoral fin disc with tiny eyes and a rectangular curtain of skin between the nostrils...
, Urolophus armatus). Stingarees are generally shades of yellow, green, brown or gray above and pale below; some species are plain, while others are adorned with spots, rings, blotches, lines, or more complex patterns.
Biology and ecology
Stingarees are slow swimmers that can often be found lying still on the bottom, sometimes partly or completely buried in sedimentSediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
. They are predators of small benthic and burrowing 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 such as crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and polychaete worms, and also occasionally small bony fishes. Studies have shown that stingarees that overlap in range differ in their diet composition, which likely serves to reduce competition. For example, off southwestern Australia the masked stingaree
Masked stingaree
The masked stingaree is a common species of stingray in the family Urolophidae, endemic to southwestern Australia. It prefers moderately deep areas of sand or seagrass some distance from shore, though it can be found in very shallow water or to a depth of...
(Trygonoptera personata) and western shovelnose stingaree (T. mucosa) feed mostly on different types of polychaetes, while the sparsely-spotted stingaree (Urolophus paucimaculatus) and lobed stingaree
Lobed stingaree
The lobed stingaree is a common species of stingray in the family Urolophidae, endemic to southern Western Australia in shallow, inshore sand and seagrass habitats. This species is plain sandy in color above and has a broad, rounded pectoral fin disc...
(U. lobatus) feed mostly on different types of crustaceans.
Like other myliobatiforms, stingarees have an aplacental viviparous mode of reproduction in which the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s hatch within the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
and are nourished first by yolk, and later by histotroph ("uterine milk") produced by the mother and likely delivered through specialized extensions of the uterine epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
called "trophonemata". For those species whose life histories have been investigated, the gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
lasts 10–12 months and the litter size is small, no more than one or two in some cases. The small litter is likely due to the relatively large size of stingaree pups, which measure around half the maximum size at birth.
Human interactions
Though generally innocuous towards humans, when disturbed stingarees can inflict a painful wound with their stout, venomVenom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous stings. Species differ in temperament; the sparse-spotted stingaree (Urolophus paucimaculatus) is reportedly more aggressive, and the spotted stingaree (U. gigas) less so. When threatened, the crossback stingaree (U. cruciatus) raises its tail over its disc like a scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
. Some species of stingarees are regularly 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...
in bottom trawls by commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
. They are generally discarded due to their small size, though some may be processed into fishmeal. Stingarees caught from shallow water likely have relatively high chances of survival, but of concern is their tendency to abort any gestating young when captured and handled.