Animal Phyla: Sponges, Cnidarians, Flatworms, Annelids and Arthropods
Sponges (Porifera)
Sponges are animals fixed to rocks. They filter water and obtain food particles from filtered water through choanocytes, specialized cells with flagella located inside their bodies.
Cnidarians
The first phylum is cnidarians. They have tentacles and can be sessile (polyps) or free-swimming (medusa). They have stinging cells called cnidocytes, which contain harpoon-like structures that release toxins on contact to stun or capture prey.
Flatworms (Platyhelminthes)
Flatworms are simple animals with organs. Some are parasites that can cause infections, such as tapeworms and flukes. Planarians are free-living, carnivorous aquatic flatworms. Tapeworms are parasitic and live in the intestines of other animals. Their structure is simple, lacking a true body cavity, and they reproduce asexually and sexually. They are considered the first major group of bilaterally symmetrical animals.
Roundworms (Nematodes)
Nematodes are worms with a slender, cylindrical body. Some cause serious diseases, such as intestinal roundworms and trichina.
Annelids
Annelids have a body divided into segments. The first segments have a mucus-covered body wall that helps them move through filaments or burrow. Annelids include earthworms and tubeworms. Some have a well-developed head with eyes, while others have a poorly developed head.
Land Earthworms and Leeches
Land earthworms have a poorly developed head. Leeches live in fresh water and feed on blood.
Molluscs
Molluscs have a soft body, normally protected by a shell. Gastropods have a single shell and can live in marine or fresh waters. Some have tentacles, a single foot, and eyes at head level. Bivalves have a body enclosed by two articulated valves, and they do not have a head. Cephalopods have a complex foot with tentacles, suckers, and beaks. They have two eyes and swim with great speed.
Echinoderms
Echinoderms live on the seafloor. Their skeleton is made of calcareous plates with spines. They show radial symmetry, many have an ambulacral system that lets them move, and water vascular tubes help them move through the sea. These animals have existed on Earth for more than 500 million years.
Types of Echinoderms
- Sea urchins: globular forms with spines.
- Sea stars: they feed on crustaceans and molluscs.
- Brittle stars: elongated arms.
- Crinoids (sea lilies): fixed to the seafloor by a stalk.
Arthropods
Arthropods are invertebrates adapted to a wide range of environments. Their body is divided into segments, and their appendages are articulated and specialized for different functions: antennae, claws, legs, jaws, and pincers. Their body is covered by a hard exoskeleton made of chitin, which they shed as they grow.
Arachnids
Arachnids have a body divided into a cephalothorax and abdomen, and have six pairs of appendages: a pair of chelicerae, a pair of pedipalps, and four pairs of legs.
Myriapods
Myriapods have many trunk rings formed by articulated segments, each with one or two pairs of legs.
Crustaceans
Crustaceans have a body divided into a cephalothorax and abdomen. Crustaceans and shellfish form two groups of lower arthropods.
Insects
Insects have a body divided into head, thorax, and abdomen. Their mouthparts are simple and the thorax has three pairs of legs. Most insects have two pairs of wings, and one pair sometimes serves to protect the body.
The biological success of insects lies in their ability to colonize wet places and other environments. Their small size and varied diets allow them to live in an environment without competing with other species. Larvae often have a different feeding habit than the adult animal.