Kids Research Express

. 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 identi

. 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

. Annelida -> Segmented worms with a muscular body wall used for burrowing. External hairs called setae aid in traction during burrowing. An internal coelom is divided into compartments by walls known as septum. The digestive system stretches from the mouth to the anus, differentiated into regions, each with a different function. Reproduction is sexual. – Examples: Lugworms, earthworms, leeches Pogonophora -> Deep-sea worms that live in chitinous tubes attached to the ocean floor. Their long, slender body has a beard of tentacles at the head end. There is no mouth or digestive system and these animals absorb all nourishment through the body surface. They reproduce sexually. – Examples: Bead worms Vestimentifera -> Giant deep-sea worms that live in chitinous tubes attached to the ocean floor. They derive nutrition using a specialized organ called a trophosome to digest sulfide-oxidizing bacteria. – Examples: Llamellibrachs Sipuncula -> Marine worms with a saclike body an

. Kinorhyncha or Echinodera -> Tiny worms with spiny bodies. An outer protective cuticle is segmented and articulated. Found in the muddy bottoms of coastal waters, they feed on microorganisms and organic particles by means of a sucking pharynx. Reproduction is sexual. Examples: Echinoderes, Condyloderes Nematoda -> Commonly known as roundworms, these animals are one of the most diverse and geographically widespread invertebrate phyla. Free-living roundworms inhabit freshwater and marine habitats, as well as soil. Parasitic roundworms prey on both plants and animals, causing widespread agricultural damage and disease. Roundworms have long, cylindrical bodies with a mouth surrounded by lips and sensory papillae or bristles. Fluid in the body cavity distributes nutrients and oxygen—roundworms do not have special respiratory or circulatory systems. Roundworms prey on other invertebrates as well as diatoms, algae, and fungi. They reproduce sexually and larvae undergo at least four

. Ctenophora -> Jellyfish-like marine animals distinguished by eight rows of cilia that propel the body in swimming. They feed on other invertebrates using two retractable sticky tentacles to capture prey. All ctenophores are hermaphroditic and reproduce sexually. Many are luminescent. – Examples: Sea walnuts, comb jellies Platyhelminthes -> Structurally simple worms with no anus or circulatory system. Known as flatworms, their flattened bodies enable internal tissues to be near the skin surface, permitting gas and nutrient exchange with the environment. A muscular layer just beneath the skin layer aids in locomotion. Flatworms are hermaphrodites and reproduce sexually. They typically have a life cycle involving a parasitic larval stage. Many types of flatworms are parasites of vertebrates. – Examples: Flatworms, flukes, tapeworms Mesozoa -> Minute parasitic animals of invertebrates, particularly squids and octopuses. These worms have a simple, elongated, ciliated body. The