It’s time to learn all about the marine rays, which are cartilaginous fish that belong to the Chondrichthyes class, of which sharks, skates, and chimaeras are also members.
This class represents one of the two large groups of fish, the other being the Osteichthians, or bony fish. The name Selachii is also sometimes used for the group containing the Sharks. Additionally we can mention that they belong to the Batoidei order which includes 534 species.
Table Of Content
Marine Rays’ Main Characteristics
These awesome creatures have a flattened, disc-like body, and their five gill openings and their mouths are usually located in their lower portion. Moreover, marine rays have large wing-shaped pectoral fins, which extend forward along the head´s sides above the gill openings.
Most of them swim and breathe differently from sharks, propelling themselves with their pectoral fins and suctioning water to breathe through large openings (spiracles) located at the top of their head, rather than through their mouth.
Their tails are usually long and thin, and in many species they have one or more sharp-edged poisonous spines, with serrated edges, which can be used to cause painful wounds. It is also important to mention that they swim very slow, which prevents them from chasing their prey and forces them to wait them on the sand.
Let´s watch them
Where Do Marine Rays Inhabit?
They are mostly marine species and are distributed throughout the world’s oceans, from the Arctic to Antarctic waters, and from shallow coastal platforms to open seas and abyssal regions.
Some of them can be found in rivers and others in estuaries, but most are marine and live near the seabed at depths of up to 3,000 m or more. Many of them are inhabitants of the bottom of their habitats, in which they usually move slowly.
What Do Marine Rays Feed On?
Marine rays feed on plankton and small animals (especially manta rays); and in some cases of fish and invertebrates, which sometimes generates damage to the seafood beds of commercial value.
Due to their slow speed, marine rays usually lay on the ground and sometimes bury themselves in the sand, where they remain motionless for a long time, waiting for the passage of a possible prey.
How Do Marine Rays Reproduce?
These really striking creatures reproduce by means of internal fertilization, since the male introduces its sperm into the female, employing its special reproductive organs (claspers), which are actually the modified edges of its pelvic fins. In general, copulation occurs between a single male and a female.
In many cases, the males bite the anterior margin of the female’s disc, in order to insert its clasper. The males of many marine rays’ taxa have sharp and pointed teeth, unlike the flat teeth of the females; which allows them to remain in contact during intercourse.
Main Types of Marine Rays
Marine rays can be classified in the following groups: electric rays, saw fish, skates and several families of rays that have slender whip tails equipped with spines, that are called Stingray or whip-tailed rays
Electric Rays (suborder Torpedinoidei)
These rays are distinguished by having big paired electric organs between the pectoral fins and the head, which they can use to apply powerful electric discharges for defensive purposes or to kill their preys. Electric rays have a smooth and naked skin.
Their head and trunk in conjunction with their pectoral fins, form a circular disc, and their tail is short and robust. Some 20 species are known to inhabit warm seas, and some reach a weight of 200 pounds (90 kg). All other types of rays, which lack electrical organs, usually have rough skin and strong spines.
Let´s meet them
Sawfish (Pristidae Family)
The rays have a snout that modifies on a sort of long sheet that possesses a series of strong teeth on each side. There are about six known species that surround the warm seas, which frequent sandy beaches and estuaries.
Skates Fish (suborder Rajoidei),
Skates fish are round or triangular with elongated noses, in contrast to the typical diamond shape of most rays. They have large pectoral fins that extend to the snout and backward, ending abruptly at the base of a slender tail.
Unlike other rays, skates produce eggs; which are large and oblong shaped with dark shells and leathery with a tendril at each corner, so they are attached to algae or other objects.
The skates lack the long, slender spine that distinguishes the stingrays. The most widespread skates belong to the genus Raja of the family Rajidae.
Stingrays
These marine rays belong to the Myliobatoidei suborder and are probably the most known marine rays. They are easily identified by their elongated and slender tails with sharp points. Most stingrays´ tails have poisonous glands, which inject an incredibly painful toxin when they sting.
Fortunately, the Stingrays only sting in self-defense. It is unlikely that a diver will be stung by a stingray unless it feels threatened. These marine rays can also be identified by their characteristic diamond shape and location, since they are often half-buried in the sand looking for food.
Many stingrays spend most of their time at the bottom of the sea; however, some of them like the case of eagle rays are seen more frequently swimming freely. These rays can be found everywhere in the world, even in freshwater.
Here they are
The remaining rays, like the stingray, comprise the suborder Myliobatoidei and consist of the butterfly rays, (Gymnuridae), stingarees (Urolophidae), Manta or devil rays (Mobulidae) and cow nose rays (Rhinopteridae).
The common characteristic of the rays of all these families is their long, slender whip-shaped tail, which usually has a spiked spine connected to a poisonous gland.
This spine is capable of causing serious wounds and is a dangerous weapon when the tails are tied. Almost all these rays are inhabitants of warm seas, with the exception of some species of rays that live in the rivers of South America.
The Marine Rays’ Evolution
Their fossil record dates back to the early Jurassic 150 million years ago. All major taxa are known for the Upper Cretaceous until the Paleocene. Most of the first fossils come from North Africa and southern Europe, areas that at the end of the Mesozoic and the early Cenozoic formed part of the Thetis Sea, (a shallow tropical sea that separates the continents from the north and south during this period)
Although the fossil record covers more than 150 million years, the record is very incomplete, due to the shortage of parts of hard bodies of marine rays. Unlike bony fish, sea rays lack large external and internal bony structures that are easily fossilized. In many cases, fossils are represented only by enlarged teeth or scales.
The teeth and scales serve to identify fossils as marine rays, but provide little information about body structure or phylogenetic relationships. Recent molecular data provide support for the traditional relationship of marine rays as a sibling group of sharks. If molecular data are correct, they suggest that sharks and rays shared a common ancestor.
