Have you ever wondered how animals survive and adapt? animals that have no bonesThese fascinating beings, known as invertebrates, make up the majority of the animal kingdom and are found in every corner of the planet, from the ocean floor to the most remote tropical forests. Their evolutionary strategies and the variety of shapes and sizes they present are truly surprising.In this article, you'll discover everything you need to know about these animals, their characteristics, classification, and some interesting facts that make them unique in nature.
The world of invertebrates The ecosystem is much broader and more complex than we might imagine at first glance. Although they sometimes go unnoticed due to their size or peculiar appearance, their importance in ecosystems is fundamental. Let's explore the particularities of this animal group in detail, breaking down the different types of invertebrates that exist and their main differences from vertebrates.
What are animals that don't have bones?
The word boneless animals to those who do not have one no articulated internal bone structure or spineThe most common scientific term to encompass them is invertebratesThey represent an overwhelming majority within the animal kingdom: according to scientific estimates, About 95% of all animal species are invertebrates, even reaching 97% in some calculations.
The absence of bones or a backbone has given rise to an astonishing diversity of body shapes and lifestyles.Their evolutionary success is largely due to these morphological adaptations. Some invertebrates develop exoskeletons (such as insects and crustaceans), others have soft bodies protected by shells (such as mollusks) and many others lack rigid protection, moving by means of muscular contractions or microscopic cilia.
Jean-Baptiste Lamarck was one of the pioneers in invertebrate zoology, distinguishing them as "animals without vertebrae." Linnaeus, for his part, also recognized the need to classify them separately from vertebrates, although his boundaries and categorizations have evolved greatly since then.
Main characteristics of invertebrate animals
The invertebrates They are distinguished, in addition to lacking a backbone, by a series of common features:
- They can be small in size, although there are colossal species such as the giant squid.
- They do not have an internal skeleton made of bones or cartilage.Instead, some have exoskeletons (arthropods), hydrostatic skeletons, or simple support structures.
- Many have shells, carapaces or hard covers for protection.
- Its morphology and physiology are extremely varied.: There are unicellular and multicellular invertebrates, with soft, segmented or branched bodies.
- They live in aquatic, terrestrial and aerial environments.. A species of invertebrate can be found in virtually any ecosystem.
The inventory of invertebrates has been a challenge for science due to its enormous variety and the difficulty to study Some species are vulnerable due to their tiny size or remote habitats. However, their biological role is irreplaceable: from plant pollination to the transformation of organic matter, including pest control and the maintenance of biodiversity.
Evolution and classification of invertebrates
Throughout history, invertebrates have been classified into various groups. With the development of evolutionary biology and genetics, these boundaries have been adjusted, but in a classical approach, we can divide the main invertebrate phyla into:
- porifera (sponges)
- Placozoa
- Cnidarians (jellyfish, corals and anemones)
- Acelomorphs
- Platelmintos (flatworms)
- annelids (worms and leeches)
- Molluscs (snails, clams, octopuses)
- Arthropods (insects, arachnids, crustaceans, myriapods)
- Echinoderms (starfish and sea urchins)
- Other less known groups: ctenophores, rotifers, nematodes, etc.
Each of these phyla represents a distinct evolutionary strategy and hosts thousands or even millions of species. For example, among the insects It is estimated that there are nearly one million described species, making this group the most diverse in the entire animal kingdom.
Prominent examples of animals that have no bones
In the vast universe of invertebrates, some groups deserve special mention for their relevance and diversity:
- Arthropods: They include insects such as butterflies, beetles and ants, arachnids such as spiders and scorpions, crustaceans such as crabs and shrimp, and myriapods such as centipedes and millipedes. Arthropods are notable for their articulated exoskeleton and its amazing capacity for adaptation.
- MolluscsThis group includes soft-bodied animals, some with shells (snails and clams) and others without (octopuses, squid). They are famous for their shape-shifting ability, their intelligence (octopuses), and their variety of habitats.
- annelids: Segmented worms, such as earthworms and leeches, play a crucial role in soil aeration and the decomposition of organic matter.
- Echinoderms: You'll only find them in marine environments. They have radial symmetry and often have external spines. Some examples are starfish, sea urchins, and sea cucumbers.
- Cnidarians: They group beings with gelatinous bodies and stinging tentacles, such as jellyfish, corals and sea anemones.
- poriferaSea sponges, organisms that filter water to feed and lack true tissues.
Each of these groups includes organisms with very different structures and functions, but they all share the primary characteristic: his life without bones.
The biodiversity of invertebrates
The biodiversity of invertebrates is staggering. Just to give you an idea, according to the IUCN and recent scientific estimates, the number of described species per class is as follows:
- Insects: 1.000.000
- Arachnids: 102.250
- Molluscs: 85.000
- Seafood: 47.000
- millipedes: 16.000
- Other invertebrates: about 109.000
In total, we are talking about more than 1.359.000 species known, although it is estimated that the real number could be much higher, since many invertebrates have not yet been described by science.
Ecological and biological importance of invertebrates
The invertebrates Not only do they stand out for their variety, but they are also key to the functioning of ecosystems. Many species are essential as pollinators, decomposers and the base of food chains. For example, insects pollinate most plants that we humans later consume, while earthworms improve soil fertility.
Another fundamental aspect is its role as bioindicators of the quality of the environment, especially freshwater macroinvertebrates. The presence of certain insects, crustaceans, mollusks or annelids in rivers, lakes and ponds allows us to evaluate the health of these ecosystems..
In addition, many invertebrates have been crucial in scientific research, such as the fruit fly (Drosophila melanogaster) and nematode Caenorhabditis elegans, helping to understand the secrets of genetics and animal development.
Reproduction and life cycles of boneless animals
The reproduction of invertebrates is as varied as they themselves. Most reproduce sexually, producing gametes (eggs and sperm). which fuse to form a zygote. However, many can also reproduce asexually by budding, fragmentation, parthenogenesis, or sporulation.
There are species that alternate between the two types of reproduction depending on environmental conditions. For example, Some species of mites have gone millions of years without sexual reproduction, perpetuating their lineage only through asexual reproduction.
Their life cycles may include complete metamorphoses, as occurs in many insects, or simple changes in size throughout life, as in molluscs and annelids.
Nervous and respiratory systems in invertebrates
The invertebrates They have much less centralized nervous systems than vertebrates. However, Very sophisticated neurons and adaptive responses have been found in many of them. For example, jellyfish have diffuse neural networks, mollusks like the octopus have complex systems capable of learning and memory, and flies have tiny but highly functional brains.
As for breathing, the following stand out: tracheal systems of insects, with a network of tubes that carry oxygen directly to the tissues. Others, such as echinoderms, They breathe through their skin or specialized gills, and sponges simply exchange gases throughout their entire body.
Macrolevels of classification within invertebrates
In practice, scientists often subdivide invertebrates into large groups to facilitate their study and understanding. The most common divisions are:
- Arthropods: Insects, arachnids, myriapods and crustaceans.
- annelids: Worms and leeches.
- Molluscs: Clams, squid, octopus, snails.
- Echinoderms: Starfish and sea urchins.
- Cnidarians: Jellyfish, corals, polyps.
- porifera: Sponges.
- Platelmintos: Flatworms.
- Nematodes: Cylindrical worms.
This classification, although traditional, serves to give a general idea of the variety of forms and styles of life.
Relationship between vertebrates and invertebrates
Life on Earth cannot be understood without considering the relationship between invertebrates and vertebrates. While the latter have a backbone and an ossified skeleton, invertebrates have developed a multitude of alternative adaptations. Both groups constantly interact: Some invertebrates serve as food for vertebrates, Others establish symbiotic relationships and some may even be parasites.
The distinction between the two groups is still widely used in education and research, although from a phylogenetic point of view, "invertebrates" do not form a single evolutionary group.
Other minor groups and curiosities
In addition to the main groups, there are minor phyla of invertebrates that are less known but equally fascinating, such as the tardigrade (microanimals capable of surviving the most extreme conditions), rotiferous (microscopic and abundant in fresh waters), and the entoprocts o nematomorphsTo better understand their role in biodiversity, you can visit our section on animals that have no bones.
It is estimated that there are thousands of species yet to be discovered, especially in underexplored regions such as the deep sea or tropical soils. However, Invertebrates are essential for the health of ecosystems and the stability of life on our planet.They exhibit an astonishing variety of forms, functions, and adaptations that demonstrate life's ability to thrive in extreme conditions and in every possible habitat.
Their role in pollination, nutrient recycling, and pest control is vital to maintaining ecological balance. The richness and diversity of invertebrates highlight the importance of conserving their habitats and promoting their study to better understand our natural environment.