The smooth butterfly ray (''Gymnura micrura'') is a species of

cartilaginous Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

in the family Gymnuridae. It is a member of the order

Myliobatiformes Myliobatiformes (), commonly known as stingrays, are one of the four orders of batoids, cartilaginous fishes related to sharks. They are members of the subclass elasmobranchs. They were formerly included in the order Rajiformes, but more recent ...

, which contains 10 total families. Its natural

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s are shallow

sea A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...

s, subtidal aquatic beds,

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

waters, and coastal saline

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s. Its common name is derived from its compressed body, pectoral fins that are wider than their length, and overall diamond shape.

Taxonomy

Gymnura The butterfly rays are the rays forming the genus ''Gymnura'' and the family Gymnuridae. They are found in warm oceans worldwide, and occasionally in estuaries. The body of butterfly rays is flattened and surrounded by an extremely broad disc f ...

is derived from Greek roots and translates into 'naked tail'. They belong to a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group of Batoid fish. This group contains over 500 other

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by h ...

fishes which includes

electric ray The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, depending ...

sawfish Sawfish, also known as carpenter sharks, are a family of very large rays characterized by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged in a way that resembles a saw. They are among the lar ...

es,

guitarfish The guitarfish, also referred to as shovelnose rays, 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 tro ...

es, skates, and

stingray Stingrays are a group of sea Batoidea, rays, a type of cartilaginous fish. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae (deepwate ...

s. They are a part of Order Myliobatiformes and are characterized by their pectoral fins being widely expanded and fused to their heads. The family Gymnuridae contains two genera which encompass 12 different species.

Description

These are broad diamond-shaped rays with a short tail that has low dorsal and ventral fin folds. The tail has three to four dark lines that are referred to as crossbars. The edges of the disc are concave. The caudal fin is never present and a variable number of tubercles can be found on larger specimens. The smooth butterfly rays have disc widths nearly twice the size of their body lengths and are very flat-bodied (compressed). The width of the rays are between 16 and 22 centimeters when they are born and are about 50 cm when mature for a female and about 42 cm for a male. Females are bigger than their male counterparts; this allows them to carry larger embryos and a greater abundance of embryos. They have a maximum size of 120 cm.

The ventral side is lightly colored while the dorsal side is variable in color. The ventral side is usually white but can contain a rusty or bronze coloration. The dorsal side can be grey, light green, brown, and also not uniform in color. They tend to use

countershading Countershading, or Thayer's law, is a method of camouflage in which animal coloration, an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptile ...

to blend in with the bottom of their environments in order to hide from predators and to catch prey. The dorsal spine on the tail is absent; therefore, no stinging can occur to harm humans.

Distribution and habitat

Smooth butterfly rays are found in the western and eastern parts of the Atlantic Ocean (Maryland to Brazil) and the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

. They are most commonly found in

neritic The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...

waters, but are also known to enter brackish

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

and hypersaline

s. They have a range that extends from the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

to 40 meters deep in tropical and warm waters. They prefer habitats that have either sandy or muddy bottoms.

Behavior and ecology

Lifecycle

These rays invest a large amount of energy into reproduction and only give birth to a few offspring; however, they give birth on a yearly basis. They use internal fertilization which is the process of the male inserting his

clasper In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's ...

s into the female's

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

to fertilize the eggs. The offspring take between two and four months to develop inside the mother. They use aplacental uterine viviparity and the young are histotrophs. The foraging strategy that these rays use is dependent on the abundance of prey in their environments. They either use opportunistic feeding where they eat what is available, or they use specialized feeding where they eat a specific organism. They tend to feed on larger prey items and swallow them whole; then they enter a long digestion time period where they feed very little or not at all. They prey mainly on

Teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

s and crustaceans, but have also been noted to consume bivalve mussels and

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

s. They use a structure called the

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...

canal; it is located on the dorsal side from the head to the pectoral fins, and are arranged in a branching pattern. The lateral line contains neuromasts that assists the rays in detecting changes in water movement. The upper jaw consists of 6 to 120 teeth and the lower jaw has 52 to 106 teeth; each jaw contains 6 to 8 simultaneously functioning rows. They are hunted by larger predators, such as sharks. The

great hammerhead The great hammerhead (''Sphyrna mokarran'') is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining an average length of and reaching a maximum length of . It is found in tropical and warm temperate waters world ...

specializes in feeding on butterfly rays and is their main predator in some areas.

Locomotion

''Gymnura micrura'' alter their swimming habits depending on where they are swimming in the water column. They tend to change between an

undulation Undulation may refer to: * Undulation of the geoid, the separation between the geoid and the reference ellipsoid of the Earth * Undulation point, a point on a curve where the curvature vanishes but does not change sign * Undulatory locomotion, ...

pattern and an

oscillation Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

pattern. They use small amplitude undulations of their fins when they are swimming along the bottom, but switch to an oscillatory approach when they are swimming freely in the water. When swimming freely in the water column, they use a quick, powerful downstroke to increase their speed; this means they move their fins down and then quickly back up. They pause after each stroke and then repeat.

Conservation

The species is currently classified as

Near Threatened A near-threatened species is a species which has been Conservation status, categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature (IUCN) as that may be vulnerable to Endangered species, endangerment in the ne ...

by the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

. It is frequently taken as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

but generally released alive. The species is fished commercially and recreationally in parts of Australia, Europe, and Asia.

References

{{Taxonbar, from=Q3017002 Gymnuridae Taxonomy articles created by Polbot Fish described in 1801