Clams

Among the invertebrates, most of the world s production is associated with mussels, oysters, shrimp, scallops, and clams. Crawfish culture is of considerable importance in the United States, but amounted to only 24,211 metric tons in 1992 (4) insignificant compared to some other invertebrate species. 

Fig. 2. Internieshing co-iotating twin-sciew extrudei A, motoi B, geai box C, feed poit D, clam shell baiiel E, vent poit F, sciew shafts G, conveying screws H, kneading paddles 1, baiiel valve and J, bhstei rings. Courtesy of APV Chemical Machinery Inc.

Asiatic clams are freshwater moUusks. They probably origiaated ia China or eastern Asia and were iatroduced iato North America and Europe ia the past century. They were originally found ia warm water but their territory now extends to Minnesota. They have not yet been seen ia Canadian rivers or lakes. 

Fig. 13. Juvenile Asiatic clams passiag through a water iatake screea.

Fig. 14. Surface coadeaser iafested with adult Asiatic clams...

Other Lethal Agents. There are a number of substances, many found in nature, which are known to be more toxic than nerve agents (6). None has been weaponized. Examples of these toxic natural products include shellfish poison, isolated from toxic clams puffer fish poison, isolated from the viscera of the puffer fish the active principle of curare "heart poisons" of the digitaUs type the active principle of the sea cucumber active principles of snake venom and the protein ricin, obtained from castor beans (See Castor oil). 

Each tubercle exhibited small clam-shell marks or growth rings (Fig. 3.30). Each ring was formed by fracture at the tubercle base during growth. Ejected internal contents rapidly deposited when contacting oxygenated waters. Tubercles were hollow (Fig. 3.31). Surfaces below the... 

Figure 3.30 Scanning electron micrograph of tubercles in Fig. 3.28. Note the clam-shell growth steps formed by successive fractures at the tubercle base. Tubercle is about 200 pm in diameter. (Courtesy of National Association of Corrosion Engineers, Corrosion 91 Paper No. 84 by H. M. Herro.)...

Shells, clams, wood fragments, and other biological materials can also produce concentration cell corrosion. Additionally, fragments can lodge in heat exchanger inlets, locally increasing turbulence and erosion-corrosion. If deposits are massive, turbulence, air separation, and associated erosion-corrosion can occur downstream (see Case History 11.5). 

Clams, mussels, and other bivalves are a serious problem in many cooling water systems. Zebra mussels and freshwater Asiatic clams are relative newcomers to the United States. Because of a lack of natural predators and prodigious reproduction rates, they have rapidly become a serious threat to the operation of many cooling water systems. 

Figure 6.15 A main mill water-strainer basket caked with clams.

Figure 6.16 Small clams lodged in heat exchanger tube inlet ends. (Courtesy of Rick Ruckstuhl, Nalco Chemical Company.)...

Pedersen patented a series of ftis-crowns related to the above except that the side chain was bound on each side to a crown. Cram " and Sutherland have both reported similar structures. Pedersen suggested the name clams for such species but the name has not found wide acceptance. 

A number of bridged crown ethers have been prepared. Although the Simmons-Park in-out bicyclic amines (see Sect. 1.3.3) are the prototype, Lehn s cryptands (see Chap. 8) are probably better known. Intermediates between the cryptands (which Pedersen referred to as lanterns ) and the simple monoazacrowns are monoazacrowns bridged by a single hydrocarbon strand. Pedersen reports the synthesis of such a structure (see 7, below) which he referred to as a clam compound for the obvious reason . Although Pedersen appears not to have explored the binding properties of his clam in any detail, he did attempt to complex Na and Cs ions. A 0.0001 molar solution of the clam compound is prepared in ethanol. The metal ions Na and Cs are added to the clam-ethanol solutions as salts. Ultraviolet spectra of these solutions indicate that a small amount of the Na is complexed by the clam compound but none of the Cs . 

Although the clam structures are of interest as ammonium ion binders, they are by no means the only azacrown compounds of interest in this application. Sutherland and coworkers have examined a number of azacrowns as primary ammonium ion bind-ers - . In addition, Metcalfe and Stoddart have utilized bis-azacrowns to bind secondary ammonium cations. 

Fe2+,Fe3+ 5000 mg 15mg Component of hemoglobin, myoglobin Liver, meat clams, spinach... 

Cr3 5 mg 0.2 mg Glucose metabolism affects action of insulin Com, clams, nuts... 

In Mollusca, bioluminescence occurs in a great variety of organisms having distinctly different appearances, such as the classes Gastropoda (limpets, snails and sea hares), Bivalvia (clams), and Cephalopoda (squids and octopuses). All luminous molluscs currently known are marine organisms, except the New Zealand fresh water limpet Latia neritoides and the Malaysian land snail Quantula (Dyakia) striata. No information is yet available on the biochemical aspects of the Quantula luminescence. 

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