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. However, a new use for the shell scraps emerged because of the cultured pearl industry in Japan. They needed tiny beads of real clam shell to implant to produce pearls. The oyster would reject other materials they tried. Shell scraps were sold to Japan. The Barry Machines were adapted to produce plastic buttons to continue the button industry. The boring sponge- Cliona- is not a predator, nor does it take any nutrients from its host. It is in competition for shelter on the ocean floor (substrate). Bivalve mollusk shells are a common host for the boring sponge. The sponge burrows into calcareous materials like corals and bivalve shells by acid etching creating a canal system (Entobia). This activity creates calcium carbonate sediment which other organisms can use to their benefit. If it covers the host shell completely, it can smother it. Or by damaging the shell covering it can weaken it to where the adductor muscles used to close the shell lose their attachment. Sponges are one of the most primitive of multi-celled animals. They have no specialized cells and no blood. They reproduce both sexually by releasing sperm into the ocean and asexually by budding. The boring sponge’s color ranges from yellow to dark brown. The color comes from hosting symbiotic dinoflagellates. Dinoflagellates are microscopic marine plankton. Dinoflagellates (Alveolata) contain chlorophyll. During daylight hours, they provide up to 90% of the sponge’s needs for metabolism, growth and reproduction through their photosynthesis. In return the dinoflagellates receive nutrients, carbon dioxide and a raised position on the seabed with access to sunlight. Let me give you some information on two of the pearl producers that I have found-Mercenaria and Panopea. MERCENARIA I believe these quahogs are not modern but date from the Pleistocene Period-Waccoma formation 1.5 to 2.0 million years ago. This is based on other fossils I found, at the same time, at North Myrtle Beach, South Carolina in November 2017. The quahog is a marine bivalve with the genus name of Mercenaria (formerly Venus). The east coast of the United States is home to two modern species: a northern variety Mercenaria mercenaria and a southern Mercenaria campechiensis which closely resembles the northern. The difference is it is slightly larger, lacks the purple coloration on the interior surface and it has no smooth areas near to its highest point on the shell (umbo). There is some interbreeding of these two species. Both have large heavy shells that they use to burrow shallowly in mud or sand. They filter feed on single celled algae and diatoms brought in through their inhalant siphon. The diatoms are filtered out by the gills and passed into the mouth by cilia. The shells have a range of color from a pale brown to shades of gray and white. The exterior is covered with a series of growth rings. The interior of the shell of M. mercenaria is colored a deep purple around the posterior edge and hinge. This purple part of the shell is called “wampum” and was used by Indians to trade for beads and other items. Reproduction begins after one year and continues thru out life. A lifespan of up to 40 years is possible. Mercenaria are prodandric hermaphrodites which means they change sex during their lifetime. Males develop first-98 % of juveniles are male. As they age and grow, the sex ratios even out. Approximately one half of the males change to female. Mercenaria both naturally grown and farmed are important commercially. At 4 to 8 years they reach 2 to 4 inches in size. Commercially named sizes: 2.0 to 2.5 “Littlenecks”, 2.5 to 3.0” Topnecks, 3.0 to 4.0” Cherrystone and 4.0+” Chowders or Quahogs. Growth ceases after 15 years. PANOPEA-GEODUCK (“GOOEY-DUCK”) These fossil Panopea bivalves lived during the Miocene Epoch 13 million years ago. It was found at Matoaka Cabins beach in Calvert county Maryland which is part of Calvert Cliffs. Panopea is a known fossil dating back to the Cretaceous Period 242 MYA. Its fossils are found world-wide. The geoduck name is native American in origin meaning “dug deep”. Modern species are native to the coastal waters of western Canada (British Columbia) and the northwest United States especially the state of Washington. It is a large, edible saltwater clam whose siphon can be over three feet in length. It is the largest burrowing clam in the world and has one of the longest lifespans of up to 168 years. It has few natural enemies which may account for its longevity. Using its long siphon, it feeds on plankton which it filters out of the seawater. The average shell size is 7 to 8 inches. Survival is due to its habit of deep burrowing. It burrows 1 foot per year until it reaches a depth of 3 feet where it lives out its lifetime. The 3+ foot siphon reaches to the top of the sea floor where it feeds. The Panopea is known for producing pearls. The clam’s shell is always open because the body and siphons are too large to be retracted into its shell. This allows pieces of material or foreign invaders to enter the mantle. These irritants prompt the production of calcium carbonate to cover up the irritation. One has a blister pearl attached near the hinge. Other pearls are on pieces of shell that look like a Panopea. The unattached fossil pearl was found in the same location and is likely from a Panopea. This pearl has been worn exposing the many concentric layers that were laid down by the clam in creating the pearl.

DISPLAY ITEMS: modern oyster with a blister pearl, modern natural oyster pearl with shell, modern natural mussel pearl with shell, fossil? (Pleistocene-Waccoma Formation 1.5- 2.0MYA)) quahog with blister pearl, fossil Miocene Panopea shell with blister pearl, fossil Miocene Panopea? blister pearl, fossil Miocene Panopea? blister pearl eroded showing concentric layers, fossil? (Pleistocene) quahog with “pearl warts” from boring sponge, pearl warts on shell, fossil? (Pleistocene) Giant Atlantic Cockle shell with blister pearl, northern quahog shell-Mercenaria mercenaria and broken pieces of “wampum”, nacreous shells: Abalone, pen shell and Turbo, shell excavated by boring sponge (Entobia). NEEDED ITEMS: modern blister pearl-nacreous, preserved boring sponge, cultured nacreous pearl, baroque nacreous pearl, preserved Panopea with siphons, dinoflagellates with microscope, “pearl” buttons

PART 3: A FASCINATING TALE: HOW BRYOZOA AND CORAL “GO MOBILE” WITH HELP FROM A HERMIT CRAB’S (PAGURUS) USE OF DEAD MARINE SNAIL SHELLS What do these look like? Do they have the outline of the shell of a snail or gastropod? See the opening or aperture? Well that is essentially what they are. But there is much more to the story of how they got to look like this. First, a marine snail dies. Second, its empty shell may become occupied by a hermit crab. Hermit crabs are decapods-10 legged crustaceans with a long spirally curved abdomen which is soft unlike the hard-calcified abdomens of crabs and other crustaceans. The hermit crab uses the empty gastropod shell to protect itself from predators. It backs into the empty gastropod shell to protect its soft parts. The tip of the hermit crabs’ abdomen has adapted to grip strongly onto the central column or axis (columella) of the snail shell. As a hermit crab grows, it needs more space meaning a larger snail shell. There is fierce competition for shells. If a hermit crab fails to find a larger shell, it likely would be eaten because it cannot fully retract into its current shell. Third, sometimes the snail shell exterior becomes home for bryozoan or stony coral polyps. These can eventually grow to completely cover the gastropod shell. The bryozoan’s or coral’s growth extends the living chamber for the hermit crab as the hermit crab moves in and out as it feeds. This symbiotic relationship greatly benefits the hermit crab enabling it to remain in its current shell. It does not have to seek out a new larger shell. An available larger shell may be difficult to find. When making a shell switch, the unprotected hermit crab is exposed, and risks being eaten. The bryozoan or coral benefits by having a solid surface for growth and a higher position to receive more light. Movement by the hermit crab provides a mobile home for the bryozoan exposing it to new sources of food. The bryozoan layers can make up 49 to 97% of the thickness of the specimens. Using a dental pick, I scrapped away the bryozoan layers to expose the original shell. This shows how small the snail shell is in relation to the overall size of the specimen. They are called bryoliths. They are beach finds from North Myrtle Beach, South Carolina. I believe they are not modern but fossils that date to the Pleistocene Period-Waccoma Formation 1.5 to 2.0 million years ago. This is based on other fossils found on the beach at the same time. Each year I would find a few. But in the fall of 2017, I found 330 over two days of low tides. Collecting In a 200-yard stretch of beach, there was one of these fossils in every depression left in the sand by the outgoing tide. This fossil is covered with coral not bryozoan. But its story is the same as the bryozoan covered shells. This example is from the Pinecrest Beds in Florida. It lived about 3.5 million years ago. The 1100 hermit crab species are divided into 2 groups: 1. Marine (1 freshwater species) hermit crabs spend most of their life underwater as aquatic animals. They live in both shallow and deep water and breathe oxygen thru gills. Hermit crabs are omnivores and feed on small fish, invertebrates including worms, plankton and other food particles in the water. A few species don’t use empty snail shells as “mobile homes” but live without moving in tubes created by worms, or in corals, sponges and tube forming, stationary gastropods. The 2nd group are land hermit crabs. They spend most of their life on land in tropical areas. They must keep their gills damp or wet, so they need access to fresh or saltwater to survive and reproduce. There are 15 terrestrial species. Their average life span is 1 to 10 years. Hermit crabs are found worldwide. They have 2 antennae and 5 pairs of legs. The first pair form chelae or pincers. The right one is usually larger and shaped to cover the shell entrance when the animal is inside. The crab walks on its 2nd and 3rd set of legs. It uses its shorter 4th and 5th pairs to grip the interior column of the snail shell Competition for a larger gastropod shell can be fierce if there is a small number of empty shells available and or a large group of hermit crabs. A unique behavioral pattern called a “vacancy chain” emerges for both marine and terrestrial hermit crabs. The chain begins when a hermit crab who needs a larger shell finds one and after trying it out finds it is either too small or too large. A hermit crab has been observed to wait nearby for up to 8 hours. Other hermit crabs arrive and inspect the empty shell. If they do not select it, they join the “chain” by holding on to one another with their claws. Up to 20 hermit crabs have been observed waiting in a “vacancy chain.” Finally, a crab selects a shell leaving its old one vacant. Simultaneously, all the crabs in the chain switch shells. If a crab is left without a larger shell, it is likely to be eaten by a predator since it cannot retract fully into its too small snail shell. Fossil hermit crabs have been found from the late Cretaceous Period 70 MYA to the present. What is a bryozoan? The bryozoans that cover these shells are invertebrate animals. Under magnification it resembles a coral with many small openings. But it is an entirely different marine invertebrate animal. Its nickname “moss animal” comes from one of their major habits of coating hard surfaces (encrusting). Bryozoa use a lophophore instead of a gill for filter feeding and respiration. They take their food out of the water using retractable hollow tentacles (lophophore) lined with cilia. The zooids are microscopic .02 on an inch long. Their body wall is made of calcium carbonate. Bryozoans form colonies composed of individuals which are connected to share food. Individuals in bryozoan colonies are not fully independent animals. Some specialize in feeding and excretion; some are hatcheries for eggs and defense. The individual animals take in oxygen and give off carbon dioxide. All the individuals are genetically identical. Most live in tropical waters and all but one is colonial. Bryozoans take 7 other forms from dome shaped, branching and free living. Colony lifespans are from one to twelve years. There are 4,000 living species but many times that number of fossil ones. They were the last major phylum to emerge in the early Ordovician Period 488 MYA. These examples are from the Class Cheilostomata which has the largest number of modern species. They produce a mineralized exoskeleton. Fossils of this class first appear in the mid-Jurassic 72 MYA and this type has been the most abundant and diverse bryozoan from the Cretaceous to the present. More recent bryozoans predominately take the encrusting form. The Paleozoic forms were erect. All species emit sperm into the water. Some release ova into the water while others capture sperm via their tentacles and fertilize the ova internally. Larva settle onto a hard surface and begin growing. The founder zooid (Ancestrula) grow new colonies by budding clones of themselves. All the individuals are genetically identical. Predators of bryozoan are sea slugs, fish, sea urchins, crustaceans and starfish.

DISPLAY ITEMS: fossil (Pleistocene Period-Waccoma Formation 1.5-2.0 MYA) bryozoan covered snail shells, fossil (Pleistocene) bryozoan covered snail prepped to expose the snail, fossil (Paleocene) coral covered snail, bryozoan colony

NEEDED ITEMS: preserved hermit crab, loaned live hermit crab, preserved bryozoan with polyps