The correct answer is Arthropoda.

Key Points

• Arthropoda is a group of invertebrate animals having an exoskeleton, a segmented body and jointed legs.
• Their body consists of segments with a pair of appendages.
• Their reproduction occurs by internal fertilization (terrestrial species) and internal or external fertilization (aquatic species).
• They have an open circulatory system.
• Types of Arthropods –
  • Insects: Ants, Aphids, Butterflies, Grasshoppers, Termites, and etc.
  • Arachnids: Scorpion, Mites, Spiders
  • Crustacean: Crabs, Fish, Lobsters, Shrimp, and etc.
• Their evolution dates back to the Cambrian period.
• They are a source of food for humans.
• They are pollinators of crops.
• Some species spread diseases to humans, livestock, and crops.
• Largest phylum of invertebrate animals.

Additional Information

• Mollusca – 2^nd largest phylum of invertebrate animals mostly found in marine and freshwater having the soft body divided into head, visceral mass, muscular foot, and mantle. Examples: Snail, Octopus, Squid, Oyster, Clams, and etc.
• Nematoda: bilaterally symmetrical, elongate and tapered at both ends; an important role in nutrient recycling in the soil feed. They cause diseases such as Ascariasis, Enterobiasis, Filariasis, and etc. Examples: Ascarids, Worms
• Echinodermata: marine animals having the star-like appearance, the skeleton of calcium carbonate, usually elongated or spherical. Examples: Starfish, Sea Urchin, Crinoids, and etc.