Metazoans: A Look at Animal Life

The metazoans are all the animals we know, multicellular organisms that have shaped ecosystems and evolved in fascinating ways. Get ready to embark on an unforgettable journey through the universe of Metazoans.

Origins and Evolution

The origin of metazoans can be traced back to a single-celled ancestor, a type of protist known as choanoflagellate. This ancestor evolved about 600 to 800 million years ago, giving rise to what we know as Metazoans.

Evolution and Diversification

Metazoans have diversified enormously since that first ancestor. This diversification occurred due to evolutionary events, environmental changes and the appearance of new habitats, giving rise to the diversity of Metazoans that we observe today.

Section 2: Classification

The Metazoan classification encompasses a series of groups, each with common characteristics. The main phyla are:

The classification of Metazoans is a complex issue due to their great diversity. However, we can organize them into several main phyla, each with particular characteristics that distinguish them:

2.1 Porifera

The porifera, also known as sponges, are the simplest Metazoans and are the first representatives of this group. Their bodies contain numerous pores that they use to filter water and obtain their food.

2.2 Cnidarians

The cnidarians They include corals, sea anemones, and jellyfish. They have stinging cells called cnidocytes in their tentacles, used to capture prey.

2.3 Platyhelminthes

The platyhelminthes or flatworms, comprise a great diversity of forms, from parasites such as tapeworms to benign tricladids or "planar worms".

2.4 Nematodes

The Nematodes, or roundworms, include the human gut nematode and the scientific model Caenorhabditis elegans. Its body is elongated and its skin forms a resistant cuticle.

2.5 Mollusks

The molluscs They represent one of the most diverse phyla of the Metazoans, with forms as varied as terrestrial and marine snails, clams, octopuses and squids. They are known for their shell and soft body divided into head, visceral mass, and foot.

2.6 Annelids

The annelids They include segmented worms such as earthworms and polychaete marine worms. Their bodies are characteristically segmented, both internally and externally.

2.7 Arthropods

The arthropods They are the most diverse and numerous phylum of metazoans, including insects, spiders, crustaceans, and myriapods. They have an articulated exoskeleton, segmented body, and articulated appendages.

2.8 Echinoderms

The echinoderms They include starfish, sea urchins, and sea cucumbers. They are known for their radial symmetry in the adult stage and their system of water tubes, used for locomotion and feeding.

2.9 Chordates

The chordates They are the Metazoa that include vertebrates, which include fish, amphibians, reptiles, birds and mammals. A distinctive feature is the presence of a notochord (at least at some stage of its life), a supporting dorsal tube.

Classification in groups and subgroups with examples

Edge	examples	main features	Subgroups
porifera	sponges	Mainly marine, they are the simplest	Calcareans, Demosponges, Hexactinellids
cnidarians	Jellyfish, corals, sea anemones	Tentacles with stinging cells	Anthozoa, Medusozoa, Myxozoa
platyhelminthes	Planarians, roundworms	flatworms	Flukes, Cestodes, Turbellarians
Nematodes	Human intestinal nematode, worm C. elegant	roundworms	Secernentea, Adenophorea
molluscs	Snails, clams, octopus, squid	Diversity of shapes and sizes	Gastropods, Bivalves, Cephalopods
annelids	Earthworms, polychaete marine worms	segmented worms	Polychaetes, Oligochaetes, Hirudinea
arthropods	Insects, spiders, crustaceans, myriapods	Most diverse and numerous phylum, exoskeleton	Insects, Arachnids, Crustaceans, Myriapods
echinoderms	Starfish, sea urchins, sea cucumbers	Radial symmetry, water tube system	Asteroids, Echinoids, Holothuroids
chordates	Fish, amphibians, reptiles, birds, mammals	Includes vertebrates, notochord	Urochordates, Cephalochordates, Vertebrates

Metazoans, although varied in form and function, share some fundamental characteristics:

1. Multicellularity: All Metazoans are multicellular organisms. This means that they are made up of more than one cell, unlike single-celled organisms like bacteria.

2. heterotrophy: Metazoans are heterotrophs, which means they cannot make their own food (as plants do through photosynthesis) and are dependent on other sources of nutrients.

3. Motion: Most Metazoans have some form of movement ability, though the degree of this ability can vary considerably. Some actively move around in search of food or mates, while others, such as sea sponges, are largely sedentary.

Reproduction and Life Cycle

Metazoan reproduction and life cycle are fascinating aspects that vary considerably between different groups. Next, we'll explore the diversity of reproductive methods and life cycles in some notable Metazoans:

Diversity in Play Modes

Metazoans use a variety of reproductive strategies to ensure the survival of their species. These strategies may include sexual and/or asexual reproduction:

1. Sexual reproduction: Sexual reproduction involves the union of sex cells (eggs and sperm) from two individuals to produce genetically diverse offspring. This method promotes genetic variability and adaptation to the changing environment.

2. Asexual reproduction: Some Metazoans have the ability to reproduce asexually, which implies the generation of new individuals from a single parent. This can occur through cell division, budding, fragmentation, or regeneration.

Examples of Life Cycles in Different Groups

Metazoan life cycles can be complex and involve different stages and morphological forms. Here are some prominent examples:

1. butterflies: Butterflies go through a complete metamorphosis. They start out as eggs, then hatch into larvae called caterpillars. Caterpillars actively feed and go through various stages of molting until they become pupae, within which internal transformation occurs. Finally, they emerge as adult butterflies and start the cycle over again.

2. jellyfish: Jellyfish have a life cycle that involves two main stages: an adult medusa stage and a polyp stage. Adult jellyfish release eggs and sperm into the water, where they are fertilized and develop into planktonic larvae called planulae. These planulae settle on the sea floor and develop into polyps, which reproduce asexually and form young jellyfish.

3. amphibians: Amphibians such as frogs and toads have a life cycle that involves an aquatic and a terrestrial phase. They begin as eggs in the water, then develop into aquatic tadpoles that breathe through gills. Over time, tadpoles undergo metamorphosis, developing lungs and limbs to adapt to life on land as adults.

The Metazoans play a crucial role in ecosystems, influencing various interactions and contributing to the stability and functionality of natural systems. Next, we will explore the role they play in ecosystems and some of the important interactions they have:

1. Nutrient recyclers: Many Metazoans, such as earthworms and decomposition organisms, play a critical role in decomposition. of organic matter and the release of nutrients into the soil, which contributes to nutrient cycling in terrestrial ecosystems.

2. Pollinators: Insects, such as bees and butterflies, play a vital role in pollinating plants, which allows the reproduction and survival of many plant species and maintains the diversity of flora in the ecosystems.

3. Pest control: Some Metazoans act as natural predators of agricultural pests, regulating their population and contributing to a balance in ecosystems. Examples include insect-eating birds and nematodes that parasitize harmful insects.

1. mutualistic symbiosis: Some Metazoans establish mutualistic relationships with other organisms, benefiting each other. An example is the relationship between sea anemones and clownfish, where the anemones provide protection for the fish and the fish provide food scraps for the anemones.

2. Predation and food chain: Metazoans participate in food chains, where they act as predators or prey. For example, lions hunt herbivores such as zebras, and in turn, are preyed on by other predators such as crocodiles.

3. Parasitism: Some Metazoans are parasites, living in or on other organisms and obtaining resources at their expense. Lice, for example, feed on the blood of their mammalian hosts.