Kids Research Express

. Mesozoa (Greek mesos, “middle”; zōion, “animal”), phylum or superphylum of life forms, sometimes thought to be transitional from unicellular to multicellular organisms. The body consists of a layer of outer cells surrounding internal reproductive cells; it contains no real organs. Except at the time of dispersal, mesozoans live as internal parasites of marine invertebrates. Some authorities consider them degenerate flatworms; others deny that they are animals. The group contains about 50 species placed in two classes or orders.

. 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