Kids Research Express

. Arthropod, animal with a hard, outer skeleton and a jointed body and limbs. Arthropods make up a phylum of invertebrates that includes insects , such as ants, beetles, and butterflies; crustaceans , such as lobsters, shrimps, and crabs; and arachnids , including scorpions, spiders, and ticks. In terms of sheer numbers and the variety of niches they fill, arthropods are the most successful animals on Earth. More than one million arthropod species have been identified—more than 20 times the number of known fish, amphibian, reptile, bird, and mammal species combined. This figure is considered a low estimate of the phylum's actual size because many arthropod species have yet to be discovered and documented. Some scientists suggest the number of arthropod species in tropical forests alone may approach six million to nine million. Traditionally, living arthropods are classified among three subphyla: the Chelicerata, Crustacea, and Unirama. Trilobites , a fourth subphylum, flourished

. Arthropoda -> Largest and most diverse invertebrate phylum characterized by animals with jointed limbs, a segmented body, and an exoskeleton made of chitin. Arthropods are abundant and successful in almost all habitats. The exoskeleton is divided into plates that enhance flexibility and movement. Periodic molting of the exoskeleton permits growth. Arthropods have a complex brain and nervous system. Many arthropods have a compound eye made up of numerous light-sensitive parts. Reproduction is sexual. – Examples: Ants, beetles, butterflies, lobsters, shrimp, crabs, scorpions, spiders, ticks Ectoprocta or Bryozoa -> Small, mostly marine animals that resemble simplified horseshoe worms, with a lophophore surrounding the mouth. They live in colonies, attaching to the sea bottom or seaweed. Bryozoans are hermaphroditic and reproduce asexually (by budding) and sexually. – Examples: Moss animals Entoprocta or Kamptozoa -> Small, mostly marine animals with a globular body mounted