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A Trilogy: Predation, Protection And A TRILOGY: PREDATION, PROTECTION AND COOPERATION: GASTROPOD, WORM AND BORING SPONGE INTERACTIONS WITH BIVALVES AND A RELATIONSHIP AMONG A GASTROPOD, A HERMIT CRAB AND BRYOZOA PART ONE: PREDATION BY MARINE GASTROPODS-SNAILS, SPONGES, CEPHALOPODS, STARFISH AND CRUSTACEONS ON MARINE BIVALVES-CLAMS AND OYSTERS. While walking the beach you will frequently come across shells of bivalves and gastropods that have small circular holes. Let us explore what made these holes. But first, what is our bivalve victim in this story? It is a soft bodied invertebrate-that means it does not have a backbone. The soft body is protected either completely or partially by a hard shell which the animal creates using a body part called a mantle that takes calcium carbonate out of the seawater. There are two hard shells which are known as valves. The valves are joined together by a flexible muscle called a ligament. The point of connection is called a hinge. The hinge has interlocking “teeth” which keep the two valves shells aligned with each other. Inside the shell are one or two muscles that pull the valves closed. When muscles are relaxed, the ligament opens the valves, allowing its foot and feeding and waste siphons outside of the shell. Common types of bivalves are clams, mussels, scallops, oysters and cockles. Now onto our villain, a marine gastropod or snail. Snails are also soft bodied invertebrates that are either protected by a single coiled or spiraled shell or unprotected like slugs that have no shell. As in bivalves, the hard shell is made by a body part called the mantle. A muscular foot enables them to move. They have a head with eyes and tentacles. Many marine snails are meat eaters or carnivorous. They prey on live bivalve mollusks such as clams and oysters and on other snails. Some snails scavenge for food from dead fish and other carrion. Examples of predatory snails are moons (Naticid, Sinum & Nautica), murex, olives (Olivia), tulips (Fasciolaria), cones, conchs, tritons and drills. Marine snails have three ways to feed on bivalves: 1. Use their snout to pry open the valves 2. Smother the clam with its large foot and or 3. Use its rasping tongue or radula to drill a hole through the clam shell and then feed on its flesh. The snail may also have an acid producing gland. The acid is used to soften the hard shell (calcium carbonate) so that drilling is easier and quicker. Perhaps one of the most common and fierce predatory snail is the moon snail (Naticid). Looking at a moon snail, it is clean and shiny. The snail’s body mantle forms two flaps that extend over its top protecting it. It burrows and hunts under the sand using its foot which it shapes into a wedge to move sand like a plow. It follows the chemical scent (chemoreception) of its prey. The moon snail can fill its foot with sea water enlarging it to over 12 inches long. It wraps its foot around its prey to suffocate it. If that fails, a gland at the tip of its proboscis produces an acid to soften the hard shell. It has a rasping tongue or radula. It does not bite its food but breaks it up by the rasping motion. The tongue has rows of very small teeth-like projections that rasp or grind up the flesh of its prey and moves the bits by its siphon into its gullet (stomach). This takes a day or more. In a lab setting, a snail feeds every 4 days or more. In looking at the drilled bivalves and gastropods, you can see that frequently drilling is done in favored locations depending on the shape of the shell and the best way for the snail to grasp its prey: Ark shells are drilled at the highest point of the shell, Lucine shells in the middle of the valve and moon snails through its largest whorl. Lightening whelks pry open bivalves using their tubular mouth and suck out the flesh. Gulf Oyster Drills (Urosalpinx) feed on bivalves and barnacles. Crabs crush snails and mollusks. Starfish use their arms to pry open bivalves. Drum fish and rays have bony mouth plates they use to crush mollusk shells. Cephalopods-octopus and squid drill holes to feed on bivalves and snails if prying them open with their arms fails. DISPLAY ITEMS: Drilled: moons, olives, arks, coquina and ---. Predators: snails: moons, baby ears, nautica, olives. Murex, tulip, drills, cones and horse conchs, and Lightening whelks. Starfish: partially crushed snail with stone crab claw. ITEMS NEEDED: NHSM Drum fish jaws, preserved snail showing body parts, snail radula (microscope to examine) PART 2: PEARLS ARE DEFENSIVE MECHANISMS CREATED BY MOLLUSKS TO PROTECT AGAINST INVADERS Invasion of marine bivalve shells and marine snails by bacteria, small aquatic organisms, worms or by boring sponges cause irritation to the soft body (mantle tissue) inside their hard shells. Mollusks which is the large grouping or phylum name for 3 major types of invertebrates- cephalopods-octopi and squid and bivalves and gastropods -snails. The last two build their shells out of calcium carbonate which they extract from sea water. When their tissue is irritated, it covers up the invader with the same material as its shell. It creates layer after layer of material forming a pearl. There are two types of pearls: nacreous, also known as mother-of- pearl, is composed of layers of the mineral aragonite and non-nacreous which are calcium carbonate concretions. Nacre or mother-of-pearl appears iridescent. Most of the nacreous pearls are made by man’s intervention introducing an irritant into the mantle of the shell. But natural nacreous pearls occur rarely in oysters, pen shells, scallops and abalone. It is estimated between 1 in 5,000 to 10,000 non-farmed oysters will produce a pearl. Nacre is strong, resilient and displays a pattern of iridescence. Nacre appears iridescent because aragonite has a more ordered crystalline structure which lets light reflect thru its layers. The layers reflect light back differently. This produces multiple colors that we call mother-of-pearl. Non-nacreous pearls are formed naturally in many types of both marine and freshwater bivalves. Aragonite and calcite are composed of the same minerals but have different crystalline structures. Many bivalve mollusks do not produce nacre. The interior of their shell is lined with calcium carbonate or calcite. Pearls produced by these shells are calcium carbonate concretions which are a dull beige to brown color. Calcite is like a thick porcelain which does not reflect and refract light. Some non-nacreous pearls are colored and can reflect light in a beautiful display called a fire pattern. Quahog (Mercenaria) pearls are purple to violet. Melo-melo shell pearls are yellow-gold. Blue mussels (Mytlius edulus) produces a purple to black pearl. Other colors are orange, white, beige and brown. These colors result from various pigments in the bivalve body. My wife found this cockle shell valve at North Myrtle Beach. It has a grouping of pinkish blister pearls. If you hold it up to the light, there are many very small holes including two through the blister pearls. Pearls have two forms: Blister pearls are attached to the interior of the shell and are irregular in shape. Free form pearls form within the mantle tissues and are not attached to their shell. Their shape is round, oval, button or irregular which is termed baroque. Pearls continue to form for the life of the animal. If you cut through the pearl, you can see the multiple concentric layers of its formation. Multiple very small blister pearls called “pearl warts” can form from invasion by a boring sponge or by worm (Trematode) larvae penetrating the mantle tissue producing tiny pits. The pits are later filled with calcium carbonate material. Growth of the bivalve’s mantle forces the parasite to move toward the outer edge of the mantle resulting in an arrangement of warts in rows which have been named “comet trails (Lauckner 1923). I am going to ask you a question and the winner gets a prize. You cannot use your cellphone for the answer. Where was the pearl button capital of the world from the 1890’s to the 1960’s? You need to give me more than a country’s name! It was Muscatine, Iowa on the Mississippi River. There was a “Mississippi River Gold Rush”. The industry lasted for 75 years. 1.5 billion pearl buttons were produced yearly. This was almost 38% of the world’s button supply. Pearl buttons were cut from freshwater clams that lived in the nearby Mississippi River. Twelve species of clams were used for the buttons. Eventually clams were being taken from rivers in 19 midwestern states. The Barry Automatic steam machine was developed to process the buttons. A machine could process 21,600 buttons daily. The buttons had to be cut out of the shell, have 2 or 4 holes drilled, be ground and polished to bring out the luster. Each button was handled 30 times. It was very labor intensive. Girls 14 to 18 sorted and sewed the buttons onto cards for sale in retail stores. Only 10% of the shell was used for buttons. Shell chips and shell dust was used by farmers as a natural insecticide, as a mineral supplement and as grit for chickens. Shell pieces were dyed for decoration in fish tanks and flower gardens. The shells were also used for jewelry such as hatpins, tie tacks and belt buckles. The creation and switch to plastic buttons began in the 1920’s and the pearl button industry collapsed in the 1960’s.
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