Mollusks (British spelling) or mollusks (American spelling) are a large collection of animals, e.g., over 110,000 living species. They are known for their decorative shells and mantles such as clams and abalone, and/or squid, cuttlefish and octopus, which are one of the more intelligent invertebrates known to man.
Mollusks have a mantle, which is simply a fold of the outer skin lining the shell, and a muscular foot that is used for motion and/or securing the individual. In many species, the mantle produces a calcium carbonate external shell, and their gill extracts oxygen from the surrounding waters and also disposes of wastes. All have a complete digestive tract that begins with the mouth and terminates with the anus. There are many having a teeth-like structure for feeding, i.e., the radula, which is composed mostly of chitin. These 'structures' are used to scrape algae off rocks, and also in the harpoon-like structures of cone snails. Squid, octopus, and cuttlefish also possess a chitinous beak.
There are ten classes of mollusks; two consist of fossilized members, i.e., Rostroconchia and Helcionelloida; and Caudofoveara and Aplacophora that contain deep-sea worm-like creatures; and, Monoplacophora, which contains deep sea limpet-like creatures, and also Scaphopoda, which relates to Tusk Shells and all not of special interest to aquarists and divers. Therefore species in those six will not be discussed here. Those of more interest are:
Class Polyplacophora (chitons; 600 species, rocky marine shorelines) Class Bivalvia (also Pelecypoda) (clams, oysters, scallops, mussels) Class Gastropoda (nudibranchs, snails and slugs, limpets, sea hares; sea angel, sea butterfly, sea lemon) Class Cephalopoda (squid, octopus, nautilus, cuttlefish)
As noted in the other sections/groupings of this Animal Library, there's room for additions, and no doubt corrections. I've laid the groundwork, so please let's not criticize; simply pitch in and help! Together we can make this 'Animal Library' for hobbyists and divers the best in the world. I should also add that since the supply of invertebrate photos from individuals appears to be somewhat scarce in certain categories, I've searched the web to find sites where none-copyrighted examples appeared to be available and/or sought permission to use their photos. I've posted these here with the website where located, such as the wonderful site at National Oceanic & Atmospheric Administration (NOAA) and www.edge-of-reef.com. By visiting the mentioned sites you might be able to gather more information about the species of interest. And if you have better photos, and/or more species information, please send it to me, as sharing is what this non-profit site is all about! (Email to saltcorner@cs.com) Also, where photos were not available, I've noted books where you can find a photo of the discussed species. - Bob
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