Limbless vertebrate animals

Have you ever confused the terms “animal” and “vertebrate”? Although it is very common in everyday life, it is something that should not happen. Roughly speaking, we could say that the first encompasses the second, but this does not mean that it has a lesser diversity of organisms. An example of this, the main theme of this article, is that not all vertebrates have limbs.

Characteristics of vertebrate animals

Vertebrate animals are a very diverse group (subphylum) within the phylum of chordates, belonging in turn to the Animal kingdom or metazoans. The most important characteristic of vertebrates is the presence of the vertebral column or notochord and their first forms of life arose in the Ediacaran period (at the beginning of the Precambrian), about 635 million years ago.

There are approximately 60,000 species of vertebrates that occupy all habitats and regions; with a great diversity of vital strategies associated with reproduction and survival. Some typical characteristics of vertebrates are the increase in body size and activity; the increase in predatory forms and the development of musculature and skeleton thanks to the endoskeleton, or internal skeleton , of cartilage or bone.

The limbless vertebrates that live in water that we currently find are those belonging to the class Agnatos (fish without jaws): the hagfish and the lampreys.

The mixines

Mixins are limbless vertebrate animals that are distributed throughout the world. They are completely cold and deep water marine, scavengers or ghouls (they feed on dying fish or dead matter). Its mucous glands are characteristic, which generate proteins and carbohydrates, which when in contact with water turn into gelatin as a defense system. They have serious overexploitation problems, being hunted to use their skin. In Spain we find the genus Myxine extending along the Atlantic coast.

Lampreys

Lampreys (whose name refers to their habit of holding onto the surface of stones with their mouths) are migratory species that inhabit cold waters in northern latitudes. Not all of them are parasites, although many are and are blood-sucking (they feed on the blood of the species they parasitize). In the Iberian Peninsula they have been reduced in some areas due to damage to fisheries. An example of them is Lampetra planeri ; critically endangered.

Amphibians without limbs

Advancing in the evolutionary line, with the jump to the terrestrial environment, we find more cases in the amphibian group: the caecilians .

These types of amphibians are adapted to underground life , so he knows little about them, and their body morphology is vermiform with a ringed body, that is, they are shaped like an earthworm . Their eyes are very small or absent and they are predators of other animals such as earthworms, ants or termites. An example is Boulengerula taitana , the first case of an oviparous species, whose young feed on the mother’s dead skin.

Within the reptiles we find a great variety of vertebrates without limbs. The first of these could be the case of pygopodia (in the same group as geckos). These have reduced hind legs and whose function has been lost during evolution; but they lack the front ones, which gives them a body morphology of the snake type. Some of them are adapted to excavation and underground life. Thus, an example of limbless vertebrate animals within reptiles is Pygopus lepidopodus .

A similar case is that of the skinks or lizards of the sands : burrowers and underground with morphology similar to that of snakes, but with traces of legs or small limbs. An example of these animals is the Lerista aericeps .

We can also find the l uciones , elongated apodal lizards from small ( Elgaria parva ) to large ( Ophisaurus apodus ), which can sometimes present reduced or vestigial limbs. Some inhabit the land and not buried.

Another example is the amfisbénidos (or lizards in two directions) can move forward and backward. They include species of blind shingles that live underground, with a solid head, the ability to burrow and slide by folding their skin like an accordion. They have no external ear and the eyes are atrophied.

And finally we come to the ofidio s or snakes , without limbs or waists except vestigial or reduced level pythons and boas. They advance by undulating movements thanks to the arrangement of the scales, the larger ones being able to approach their prey through rectilinear movements. The lower jaw, joined by muscles and skin, can be opened or dislodged to ingest large prey and have a specialized dentition, which allows them to inoculate powerful poisons and hold their prey. They hunt using chemical senses, such as their forked tongue and lateral stimulus receptors that act as infrared detectors.

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