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15.7: Marine Animals in Benthic Environments - Mollusca

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    10396
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    Mollusca

    Mollusca (or mollusks) are a very diverse groups of animal with at about 85,000 living species. Mollusks are the largest marine phylum, comprising about 23% of all known marine organisms. Mollusks include clams, scallops, oysters, mussels, limpets, chitons, and snails (snails are gastropods—the account for about 80% of invertebrate species). Cephalopods are mollusks and include octopuses, squid, cuttlefish, and nautilus.

    • Mollusks all have unsegmented soft bodies with a "head" and a "foot" region (they may not look like a head or foot!).
    • Often their bodies are covered by a hard exoskeleton, as in the shells of snails and clams or the plates of chitons.
    • Many have shells, either calcareous, or made of proteins and chitin.
    • Most mollusks have eyes.
    • Mollusks have a mantle with a body cavity (used for breathing and excretion), and the presence of a radula (something tongue-like).
    • All mollusks larvae nervous system, blood circulation system, and often complex digestive system.
    • All produce eggs that emerge as larvae or miniature adults.

    Mollusks appeared in the Cambrian Period and have diversified into their multiple forms. A large group called ammonites dominated the oceans during the Mesozoic era, but vanished with many other species at the K/T Boundary extinction event. Their distant relatives, squids, that do not have calcareous shells, survived the K/T extinction event. Another distant relative, the nautilus, also survived the K/T event.

    Examples of Mollusks
    Clam Scallop oysters Blue Mussels
    Figure 15.21. Clams Figure 15.22. Scallop Figure 15.23. Oysters Figure 15.24. Mussels
    Giant clam limpet Chiton nudibrach
    Figure 15.25. Giant clams Figure 15.26. Limpet Figure 15.27. Chiton Figure 15.28. Nudibrach
    gastropod conch Cowrey Nautilus
    Figure 15.29. Gastropod Figure 15.30. Conch Figure 15.31. Cowrie Figure 15.32. Nautilus
    Octopus Squid Ammonite Bellemnites
    Figure 15.33. Octopus Figure 15.34. Squid Figure 15.35. Ammonite (extinct) Figure 15.36. Belemnites (extinct)
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