Chondrichthyans, also called cartilaginous fish, are a group of very ancient aquatic vertebrates, and although they are not as numerous or as As diverse as bony fish, their morphological adaptations, their swimming muscles, sensory organs, powerful jaws, and their predatory habits have given them a strong ecological position in the environments where they live.
Beyond the fact that they derive from ancestors with a bony skeleton, chondrichthyans lack ossification in their bones, so they have a cartilage skeleton, and this is its main distinguishing feature. If you want to know about the other characteristics of the cartilaginous fish , their names and examples, continue reading this article on our site and we will tell you all about it.
Main characteristics of cartilaginous fish
There are two types of cartilaginous fish. Next, we will describe its main characteristics:
Elasmobranchs (sharks and rays)
This group includes sharks and rays. Some of them are carnivores that locate their prey through olfactory organs, since they have poorly developed eyesight Currently, there are 8 orders of sharks with more than 400 species and 4 orders of rays with almost 500 species. In the case of sharks, most have the following characteristics:
- Body: a fusiform body, in front a sharp rostrum with a ventral mouth. At the end of the body there is a heterocercal tail, that is to say that it has two lobes of different shape and structure, one of them containing the end of the vertebral column, and in front there are a pair of pectoral fins, a pair of pelvic fins and a pair of fins. two unpaired dorsal fins. In males, the pelvic fins are modified anteriorly as a sexual organ for copulation and are called myxopterygians, pterygopodia, or claspers.
- Vision, skin and receptor organs: they have paired nostrils, ventral and anterior to the mouth. The eyes lack eyelids, although some species have a nictitating membrane, and have a spiracle behind each one. The skin is hard and similar to sandpaper in some species, it has placoid scales, also called dermal scales, which are arranged in a way that reduces turbulence, facing backwards. Along the body and head they have neuromasts, receptor organs that are extremely sensitive to vibrations and water currents. They also have special receptors that allow them to detect their prey by the electric field they emit, and they are the ampullae of Lorenzini that are located on the head.
- Dientes: the teeth are not fused to the jaw and have two rows, the back one replacing the teeth that are lost from the row in front, and in this way they always have new teeth. These, depending on the species, can have a serrated shape, to cut their food, sharp with a grasping function and in the case of ray species, there are flat teeth that allow them to scrape on surfaces.
- Skeleton and swim: they have a mineralized cartilaginous skeleton, and not bony as in the rest of the fish. In addition, they do not have a swim bladder, and this means that they are constantly swimming or staying still at the bottom, since otherwise they would sink. On the other hand, they do have a voluminous liver that contains lipids (squalene), which also prevents it from sinking.
Holocephali (chimeras)
This small group is made up of approximately 47 species today. Anatomically it has a mixture of elasmobranch and bony fish characters:
- Body: they have a very curious shape, their body is elongated and the head is protruding and they have a clasper-like structure, which allows them to hold the female during copulation. Its snout resembles that of a rabbit and its tail is whip-shaped.
- Jaw and teeth: they do not have teeth, but rather wide and flat plates. The upper jaw is completely fused to the skull, unlike the others, and that's where its name comes from (holo=total, all and cephalo=head).
- Size: they can reach up to 2 meters in length.
- Defense: Its dorsal fin has a poisonous spine.
- Food: Their diet is based on crustaceans, molluscs, echinoderms, small fish and algae, a mixture of foods that they grind feed.
The rest of the characteristics regarding their reproduction and trophic ecology are similar to the rest of the chondrichthyans.
How do cartilaginous fish swim?
As already mentioned, elasmobranchs have dermal scales that allow them to reduce turbulence while swimming. On the other hand, along with their lipid-laden livers, air-swallowing ability, and fins, they become excellent swimmers and these adaptations allow them to stay on the water column. The odd fins allow it to roll and the even fins control it. On the other hand, the caudal fin, being heterocercal, allows it to control thrust and produce suspension force.
In the case of rays, they are all adapted for life in the bottom of the water, and their bodies have a flattened shape and with the paired fins enlarged and fused to the head, which function as wings when swimming. Their teeth are flattened and capable of scraping surfaces and grinding their food, which is often crustaceans, molluscs and often small fish.
Their whip-like tails end in one or more spines that are connected to venom glands in some species. They also have electrical organs on each side of their heads that produce shocks that can stun prey or predators.
In addition to knowing how they swim, we invite you to know how sharks sleep?
Reproduction of cartilaginous fish
Cartilaginous fishes have internal fertilization and different reproductive modalities that we will see next:
- Oviparous: they lay eggs loaded with yolk immediately after fertilization. Many sharks and rays lay their eggs in a horny capsule whose ends form tendril-like filaments that help them adhere to the first firm object they touch, and the embryo can be inside for anywhere from 6 months to 2 years. Generally, this modality occurs in small and benthic species, and they can lay up to 100 eggs.
- Viviparous: they develop an authentic placenta from which the embryo is nourished. This reproductive mode has facilitated this group's evolutionary success. It occurs in almost 60% of chondrichthyans and in large and active species.
- Ovoviviparous: hold the embryo in the oviduct while it develops and feeds on its yolk sac until it is born. In turn, it presents different types of feeding for the embryo, such as lecithotrophy, where the embryo is nourished by the yolk; histotrophy, where the embryo or embryos are nourished from a fluid (histotroph) produced by villi on the inner surface of the uterus. On the other hand, there is oophagy, where the embryo feeds on fertilized eggs while they are inside the uterus; and, finally, there is adelphophagy or intrauterine cannibalism, where the strongest embryo that hatches first eats its hatched or hatched siblings.
They have no parental care, so once the embryos hatch, they fend for themselves.
Names and examples of cartilaginous fish
The chondrichthyans (khondro=cartilage and ikhthys=fish) are a class of vertebrates that includes the subclasses Elasmobranchs (sharks, rays) and Holocephalians (chimeras), and between both groups it is estimated that there are more than 900 species, most of them marine and some freshwater or euryhaline, that is, waters that have different concentrations of s alts.
Examples of sharks
Sharks are divided into a large number of species, so here we will name their current 8 orders and examples of each of them:
- Heterodontiformes – Horned sharks such as Heterodontus francisci are found here. They are small in size and inhabit warm and temperate waters of the Indian Ocean and western Pacific, they are absent in the Atlantic.
- Scualiformes: the species that make up this group lack a nictitating membrane and an anal fin. They inhabit deep waters of the Atlantic Ocean. They are medium-sized and some species have poisonous spines on their dorsal fins, such as Squalus acanthias.
- Pristioforiformes: this group includes the so-called sawsharks. They have an elongated and serrated face in the shape of a saw that serves to stir in the mud and look for their food, which is based on squid, shrimp and small fish. An example is Pristiophorus japonicus, typical of Japan.
- Squatiniformes: includes angel sharks, they have a flattened shape and wide pectoral fins, reminiscent of rays, such as Squatina squatina, also called angelfish. They have a fairly wide distribution, since they are found in the Atlantic Ocean, the Mediterranean Sea, the Dead Sea and the North Sea. Some species can perform migrations.
- Hexanchiformes-This includes the most primitive sharks in existence today. One example is Hexanchus nakamurai, the big-eyed cow shark, which is found in the Atlantic and Indian Oceans. Although it looks dangerous, it feeds on invertebrates and is harmless to humans.
- Orectolobiformes: These are warm-water sharks with short snouts and small mouths. They inhabit the seas and oceans around the world. This includes the largest shark in existence, the whale shark Rhincodon typus. It inhabits warm tropical and subtropical waters, it feeds by filtration, which in addition to its appearance, makes it similar to whales.
- Carcharhiniformes: This order is the most diverse, found in tropical, temperate, and deep waters around the world. It has an elongated snout and a large mouth, it has a nictitating membrane that protects the eyes. This includes one of the best-known sharks, such as the Galeocerdo cuvier tiger shark, which bears its name due to the stripes on its sides and back.
- Lamniformes: they are the best known sharks, such as the white shark Carcharodon carcharias, famous for being a species that frequently attacks humans. It lives in warm and temperate waters of almost all oceans.
Examples of dashes
The stripes are classified in 4 orders:
- Rajiformes: These are the so-called true rays. Species can be found in all oceans, from the Arctic to the Antarctic. Here, for example, are the freshwater stingrays Potamotrygon motoro, an inhabitant of tropical waters in South America. Feared for the sting they have at the end of their tail fin, since attacks on humans have been recorded.
- Pristiformes: they are called sawfishes, since they have a long snout full of teeth, like Pristis pectinata, which also has a flattened body and winged pectoral fins. They inhabit tropical and subtropical waters around Africa, Australia, and the Caribbean and hunt at night. They should not be confused with shark rays, as they belong to another group.
- Torpediniformes: These are commonly called Torpedo Rays or Electric Rays, as they can produce an electric shock to stun their prey or predators by electrical organs located at the base of the pectoral fins. They are inhabitants of all the temperate and tropical seas of the world, such as the Torpedo torpedo that lives in the waters of the Atlantic Ocean and the Mediterranean Sea.
- Myliobatiformes: is a group closely related to the Rajiformes, as they are very similar to them. They are the largest rays in the world, and here the manta ray Mobula birostris is included, they lack a stinger in the caudal fin. They live in warm-water seas around the world.
You may also be interested in this other article on our site about Animals of the deep sea.
Examples of holocephalians
Holocephalians are classified in only one order, the Chimaeriformes, a group that includes the chimaeras or ghost fish. There are only three families here:
- Callorhynchidae.
- Rhinochimaeridae.
- Chimaeridae.
There are few differences between them, some species have a very long snout with nerve endings that allow them to detect small prey. An example is the common chimaera Chimaera monstrosa, which inhabits the Atlantic Ocean and the Mediterranean Sea.
Now that you know more about cartilaginous fish, we encourage you to read this other article about 9 animals without bones.
