By Bob Goemans
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 Tridacna crocea (Boring Clam, Crocea Clam)

Tridacna crocea
Lamarck, 1819

Boring Clam, Crocea Clam

Likely Reef Tank Suitable

Likely Fish-Only Tank Suitable


Those animals in the Phylum Mollusca, (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)

And in this grouping, those in the Class Bivalvia will be discussed.

Finally, to repeat here, as many in this portion of the Library are maintained purposely in hobbyist aquariums, light intensity and the strength of water movement is paramount to their well being. Therefore I'll repeat light intensity and the strength of water movement as denoted in the opening to the Anemone Section of the Species Library;

As to PAR impact, there are shallow water/fringing reef stony corals/anemones that require certain levels light to remain healthy/colorful, such as a PAR value of about 400 - 800. Then there are soft and stony corals/other animals liking medium light, such as a PAR value in the range of 100 - 400. As for the low light corals, such as mushrooms and others, they prefer a PAR value of about 50 - 100. For water motion, I've decided to relate it to the visible intensity of water motion on that of a long tentacle anemone. No visible tentacle motion is '0,' whereas a slight movement of some tentacles is '1.' If all the tentacles are gently swaying in the current it is '2.' If all tentacles are moving fairly fast and bouncing into each other it is '3.' Should all tentacles be driven with such force they are extended in one direction or unable to sway back to their central position it's '4.' Try to keep these values in mind, but if necessary revert back to this paragraph, as you will see them as - PAR - XXX & WM - X. Hopefully you'll find this quite helpful.

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