Invertebrates PDF

**Invertebrates** Did you know that invertebrates are the most numerous group of animals? They constitute 95 percent of known organisms in the animal kingdom. Invertebrate animals are multicellular and lack a backbone. They are divided into six groups. **Porifera or Sponges (examples: sea sponge)*...

**Invertebrates** Did you know that invertebrates are the most numerous group of animals? They constitute 95 percent of known organisms in the animal kingdom. Invertebrate animals are multicellular and lack a backbone. They are divided into six groups. **Porifera or Sponges (examples: sea sponge)** Porifera or sponges are very unusual organisms. They look like plants but are invertebrate animals. Their body is simple: they have no tissue or organs. They don\'t have a brain, head, blood, organs, or muscles. They vary in color, size, and shape. However, they do live a long time, as there are hardly any predators that consume them. Some porifera produce chemicals for protection; this makes them toxic to other organisms. Porifera are aquatic. Some live in freshwater, while others have adapted to live in saltwater. When they\'re young they\'re mobile larvae, but as adults they don\'t move from where they live. Porifera obtain food from the water around them. The surface of their body is covered in pores, through which they absorb water and oxygen, as well as discard waste. **Coelenterates (examples: sea anemone, fan coral)** Coelenterates are aquatic invertebrates. Most are marine (they live in saltwater). The main haracteristic of these animals is that they have an opening in the center of their body, through which they feed. This opening is surrounded by tentacles that they use to trap their prey. Although they have no brain, coelenterates have a simple nervous system. They reproduce sexually or asexually. Most of them produce toxins to protect them from predators and to paralyze their prey. They\'re beautiful, but it\'s best to admire them from afar, as the toxins that some of them produce can cause us a lot of pain, itching, and swelling. In Australia and other places, they can be fatal. Jellyfish, sea anemones, and corals are part of this interesting group of animals. **Worms** Worms are invertebrate animals with long, soft bodies. Occasionally, their body is divided into rings. They have no limbs and move by sliding or contracting. Worms are the most abundant animals on Earth. They can live underground, in the water, or in humid places. They don\'t have lungs: they breathe through the skin. Their predators include birds and salamanders. Although they have a mouth, they don\'t have teeth. However, they do eat a lot! They\'re also very valuable to agriculture, as they nourish our soil by eating and decomposing plants and dead animals, bacteria, and fungi. They can reproduce sexually or asexually. **Mollusks (examples: slugs, squid)** Mollusks can live on land and in the sea, and they have a soft body. Some have a very hard external shell that protects their body. Some have only one shell, like the queen conch and garden snails; others have two-layered shells, like clams. We can also find mollusks with no shell, like slugs. Have you noticed how a snail moves? Mollusks that crawl have a foot that helps them to move. They also have lungs that allow them to breathe. Mollusks that live in the water, like squids and octopuses, move and swim by propulsion: they expel water from the body. Have you seen how squids or octopuses swim? **Arthropods** Around 75 percent of animals belong to this group. Arthropods are distinguished by the presence of a shell, which is an exoskeleton that protects them. Their body is also divided into parts: legs and appendages with joints. Arthropods are cold-blooded and can live on land or in water, or fly. These tiny animals have very good eyesight and hearing. They use their antennae to monitor movement, heat, or vibrations around them. They also use them to smell and taste food, among other uses. Arthropods are classified into four subgroups: insects, arachnids, crustaceans, and myriapods. - They usually have six legs. - They have two antennae. - They have eyes on each side of the head. - Some, like bees, produce toxins. - They have eight legs. - They don\'t have antennae. - Their body has two parts: the cephalothorax and the abdomen. - Some have more than two eyes. - They feed on insects and other small animals. - Many are venomous. - Most live in water. - Their body is divided into the cephalothorax and abdomen, and they have a very strong shell. - They have two antennae on the head. - Most have ten legs. - The front legs of some are in the form of pincers, which helps them defend themselves and obtain food. - They have two antennae, but more than twenty legs. - Their body has rings, and each ring has two legs. - Some are venomous. **Echinoderms (examples: starfish, sea lilies, sea urchin)** Starfish, sea urchins, and sea cucumbers are animals classified into the same group: echinoderms. The group\'s name comes from the Greek words echinos and derma, which mean spiny and skin, respectively. Clearly, this name refers to the rigid and spiny surface typical of these invertebrate animals. Echinoderms live in water. They usually have a star or round shape, but have no distinguishable head. They have small feet that help them to move on the sea floor. Some have an internal skeleton formed of **calcareous** plates. On these plates, there may be spikes or spines. They reproduce sexually and begin life in a larval state. Some live on rocks or corals, while others can be found in the sand on the sea floor. calcareous: made of calcium carbonate Interesting Facts about Echinoderms - Around 7000 species of echinoderms are currently known to exist. - They have no heart or blood. - Although they move slowly, they can swim and crawl thanks to their arms. - Not all echinoderms have five arms, like starfish.