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April 5, 2017

Molluscs have such diverse shapes that many textbooks base their descriptions of molluscan anatomy on a generalized or hypothetical ancestral mollusc. The Tasmanian giant crab is long-lived and slow-growing, making it vulnerable to overfishing.[72]. Likewise, the relationships between various arthropod groups are still actively debated. At the time these were interpreted as evidence that the modern phyla had evolved very rapidly in the Cambrian explosion and that the Burgess Shale's "weird wonders" showed that the Early Cambrian was a uniquely experimental period of animal evolution. The earliest animals were marine invertebrates, that is, vertebrates came later. Arthropods' primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph - analogue of blood - circulates; they have open circulatory systems. The Crustacean Fisheries group is responsible for providing information on blue crab, stone crab, shrimp, and horseshoe crab fisheries in Florida. Thirdly, it has a nervous system including a complex digestive system using microscopic, muscle-powered hairs called cilia to exude mucus. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Trilobites, now extinct, roamed oceans for 270 million years. [17] A re-analysis of fossils from the Burgess Shale lagerstätte increased interest in the issue when it revealed animals, such as Opabinia, which did not fit into any known phylum. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Scientists have proposed many conflicting ideas about how arthropods evolved and diversified. Horseshoe CrabsHorseshoe crabs are important to both coastal communities and human health. They form a phylum which includes insects, arachnids, myriapods, and crustaceans. What kind of symmetry do arthropods have? Arthropods' methods of reproduction and development are diverse; all terrestrial species use internal fertilization, but this is often by indirect transfer of the sperm via an appendage or the ground, rather than by direct injection. Further, it is held by some scientists that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution. [52], Giant tube worms cluster around hydrothermal vents. Which of the following is dorsoventrally flattened? Sponges do not have nervous, digestive or circulatory systems. [51] Their numerical dominance, often exceeding a million individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of life cycles, and their presence at various trophic levels point at an important role in many ecosystems. These classes include gastropods, bivalves and cephalopods, as well as other lesser-known but distinctive classes. Florida Fish and Wildlife Conservation Commission • Farris Bryant Building Cnidarians include corals, sea anemones, jellyfish and hydrozoans. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells.

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