Types of Invertebrates
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Zoologists (scientists who study animals) classify invertebrates into about 30 major groups, known as phyla. These phyla vary enormously in the number of species they contain. Arthropods (phylum Arthropoda) are the invertebrate phylum with the most species—more than one million known species and countless more awaiting discovery. The mollusks (phylum Mollusca) make up the second largest group of invertebrates, with at least 50,000 species. Among the simplest invertebrates are the sponges (phylum Porifera). Other major invertebrate phyla include the cnidarians (phylum Cnidaria), echinoderms (phylum Echinodermata), and several different groups of worms, including flatworms (phylum Platyhelminthes), roundworms (phylum Nematoda), and annelids (phylum Annelida).
Invertebrates Phylum:
Placozoa -> Microscopic marine animal. Flattened body composed of two outer layers of flagellated cells enclosing loose cells. Reproduces asexually and possibly sexually. – Examples: Single species identified as Trichoplax adherens.
Porifera -> Simple, multicellular animals with tissues but no distinct organs. Commonly known as sponges, they typically attach to rocks, shells, or coral. Most sponges have an irregular shape supported by a skeleton composed of calcareous crystals, silicon spicules, or spongin fibers. Most sponges have an internal water canal system that moves water through the body, providing a constant supply of food particles and oxygen to all cells and removing wastes. Sponges reproduce sexually. They regenerate lost or injured body parts. – Examples: Sponges
Cnidaria -> Aquatic radially symmetrical animals with tentacles encircling the mouth at one end of the body. Cnidarians appear in two forms during their life cycle, the sessile, cylindrical polyp and the free-swimming medusa that looks like a jellyfish. Most feed on zooplankton, although some eat larger invertebrates. Cnidarians use tentacles to capture prey, immobilizing the prey with stinging cells called nematocysts. Cnidarians reproduce both asexually (by budding) and sexually. Some species are hermaphroditic, with both eggs and sperm produced in each individual. Most regenerate lost or injured body parts. – Examples: Coral, hydra, jellyfish, Portuguese man-of-war, sea anemone
Invertebrates Phylum:
Placozoa -> Microscopic marine animal. Flattened body composed of two outer layers of flagellated cells enclosing loose cells. Reproduces asexually and possibly sexually. – Examples: Single species identified as Trichoplax adherens.
Porifera -> Simple, multicellular animals with tissues but no distinct organs. Commonly known as sponges, they typically attach to rocks, shells, or coral. Most sponges have an irregular shape supported by a skeleton composed of calcareous crystals, silicon spicules, or spongin fibers. Most sponges have an internal water canal system that moves water through the body, providing a constant supply of food particles and oxygen to all cells and removing wastes. Sponges reproduce sexually. They regenerate lost or injured body parts. – Examples: Sponges
Cnidaria -> Aquatic radially symmetrical animals with tentacles encircling the mouth at one end of the body. Cnidarians appear in two forms during their life cycle, the sessile, cylindrical polyp and the free-swimming medusa that looks like a jellyfish. Most feed on zooplankton, although some eat larger invertebrates. Cnidarians use tentacles to capture prey, immobilizing the prey with stinging cells called nematocysts. Cnidarians reproduce both asexually (by budding) and sexually. Some species are hermaphroditic, with both eggs and sperm produced in each individual. Most regenerate lost or injured body parts. – Examples: Coral, hydra, jellyfish, Portuguese man-of-war, sea anemone
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