Among the most successful of all marine animals, mollusks display great diversity and a remarkable range of body forms, allowing them to live almost everywhere from the ocean depths to the splash zone. They include oysters, sea slugs, and octopuses. Some species lack eyes and shells and live passively in sediment or on the seabed. Others are intelligent, active hunters with complex nervous systems and large eyes. Filter-feeding mollusks, such as clams, are crucial to coastal ecosystems, as they provide food for other animals and improve water quality and clarity. Many mollusks are commercially important for food, pearls, and their shells.
A.
Overall Anatomy : Most mollusks have the following body parts: a.
Head b.
Soft body mass – Mollusks have a hydrostatic skeleton – their bodies are supported by internal fluid pressure rather than a hard skeleton. They all have a mantle, a body layer that covers the upper body and may or may not secrete a shell. All Bivalves and snails, however, have a shell as well. c.
Muscular foot – the foot is formed from the lower body surface and helps it to move. The mollusk phyla are divided by the foot…
B.
Groups : a.
Bivalves – “Two-Shelled”
Bivalve Anatomy - The shell of bivalves (clams and relatives) has two halves jointed by a hinge.
These can be held closed by powerful adductor muscles while the tide is out or if danger threatens.
The siphon is a tube that can extend from its shell to reach the surface while buried in the mud. It contains photoreceptors on the outer edge, acting as a simple eye, detecting light and dark. The muscular foot is used for burrowing in the sand. Some bivalves move by clapping their two shells together, producing jerky movements. b.
Cephalopods – “Head Foot”…We will look at this group at a later time. c.
Gastropods – “Stomach Foot” …We will look at snails, but not sea slugs at this time.
Gastropod Anatomy – The body plan for snails features a head, large foot, and usually a spiral shell. All the soft body parts can be withdrawn into the shell for protection, or to conserve moisture while uncovered by the outgoing tide. To move, they glide across surfaces using their mucuslubricated foot.
C.
Feeding – The ways in which mollusks feed are very varied. a.
Sea snails have a rasping mouthpart, or radula , which is unique to mollusks. The radula has reinforced piercing “teeth” and is used to remove algae from rocks (other mollusks use the radula in different ways, but we’ll get to that) b.
Most bivalves create water currents through their siphons. They filter food from the moving water with their mucus-covered gills. Thus, bivalves are called “filter feeders”.
D.
Respiration
Most mollusks breathe using gills. Those bivalves that live in areas that are sometimes exposed to the air must keep their gills moist. At low tide, bivalves close their shells but retain a little water inside. Some gastropods clamp down against rocks or other shells to retain moisture.
E.
Reproduction and lifestyle
In most cases, reproduction involves releasing egg or sperm into the water (external fertilization). There is no parental care after this point. The eggs hatch into shell-less larvae, which live in the plankton. Only those that land in a suitable environment survive to reach sexual maturity. Individuals may be of separate sexes or hermaphroditic (having both male and female reproductive organs). Eggs, however, must still be fertilized by a different partner. Some can change sex with age. Oysters can change sex several times in a breeding season.

D
ESCRIPTION
Lightning whelks reach a length of 2.5 to 16 inches (6 to 40 cm). Their distinguishing characteristics include their off-white to tan or gray shell with narrow, brown "lightning" streaks from the top of the shell to the bottom. The shell is white on the inside. The animal inside the shell is dark brown to black. Lightning whelks are unusual in that they have a counterclockwise shell spiral (lightning whelks are usually called "left handed").
L IFE H ISTORY
They consume bivalves (invertebrates with two shells), especially oysters, clams, and scallops, as the mainstay of their diet. Among the lightning whelk's predators are gulls, crabs, and other whelks. Their mating season is from late October to early January. Spawning season is from March through April. The female lays eggs in long strings of capsules 11 to 33 inches (27 to 83 cm) long. Each strand has up to 145 capsules and each capsule may contain 20 to 100 eggs. Only about 8 to 13 of the eggs in each capsule hatch. Juveniles will begin hatching in May and emerge as tiny lightning whelks. Their life span is unknown.
The carnivorous habits of the whelks begin as hatchlings. The whelks that hatch feed on the eggs that did not hatch. When feeding, an adult whelk will try to pry open a bivalve by inserting the edge of its shell inside the bivalve and using it like a crowbar. If it cannot pry the bivalve's shell open this way, it will grind the shell with its own shell until it creates a hole large enough to insert its radula (toothed tongue). The lightning whelk can "smell" its prey with special sensory organs inside its body and will almost completely bury itself searching for other food.
Like snails, the lightning whelk is in the class Gastropoda which means "stomach footed". Gastropods are univalves (have only one shell). Hermit crabs often make homes of unoccupied lightning whelk shells. A lightning whelk leaves behind a trail when crawling. It is often easy to track them. The shell grows very quickly when the whelk is young as long as food is abundant. As it gets older, the shell grows more slowly. The color of the shell depends greatly on light, temperature and age. Older whelks have pale shells.
H ABITAT
Lightning whelks may be found on the bottom of shallow bays in sand or mud near shoalgrass or turtlegrass meadows.
D ISTRIBUTION
O
THER
The lightning whelk's shell is a treasure that can often be found along the Gulf Coast from North
Carolina to Texas.
Native Americans harvested whelks for religious ceremonies and practical tools. Many tribes believed that the "left handed" spiral made the shells sacred objects, but whelks were also eaten and their shells used as scrapers, gouges and even cups and bowls. Some larger shells can hold up to one quart of liquid.
It is believed that sailors even used the egg cases as sponges for bathing. The lightning whelk shell is recognized as the official Texas State Shell.

Crawling beneath the sand, leaving a furrow, moon snails or "cat's eyes" have a greatly expanded foot which they use to engulf bi-valves; they drill through their shells with a moving ribbon of rasping teeth. A circular
"collar" of eggs cemented with sand grains can often be found on the low tidal flats in Spring and Summer. Class: Gastropoda , Family:
Naticidae/moon & ear shells
If you find a small, white ear-shaped shell on the beach, you have found the hidden beauty of the Ear Snail. The living snail is unable to draw its voluminous foot into its shell, so for protection it stays buried in the sand. At low tide, if you find a broad, semi-circular furrow in the sand, dig down a few inches, and you'll probably find the Ear Snail, oozing along, searching for a meal of small clams. Class: Gastropoda Family: < Ear and Moon>
is a particularly hardy and attractive gastropod that is found around oyster reefs and mud flats in West Florida.
Its handsome, pointed spiral shell is used extensively in shell craft. Tolerant of low salinities, Melongena is excellent for feeding demonstrations: food is placed in a test tube and the gastropod extends its long, snakelike probocis down to get it. Occasionally it feeds on live oysters. Size: 6-10 cm.

These highly polished, brightly colored snails with barber shop whorls feed on other small snails. They use their sharp operculums (the door that seals the shell) to slash at their prey. Their vase-shaped egg cases are commonly seen all over the grass flats in the Spring. Class: Gastropoda Family: Fasiolariidae/tulips and horse conchs
Unlike other bivalves, scallops can swim, and fairly quickly. They move a jet of water past the shell hinge, propelling it forward.
Scallops have fan-shaped shells, often with ridges or ribs. At the bottom of the shell, there are two auricles, or "ears." Scallops have about 60 eyes that line its mantle. These eyes may be a brilliant blue color, and allow the scallop to detect light, dark and motion. Scallops eat by filtering small organisms out of the water. As water enters the scallop, mucus traps plankton in the water, and then cilia moves the food into the scallop's mouth. Scallops are found worldwide, and they may live from the intertidal zone to the deep sea. Many scallops are hermaphrodites - they have both male and female sex organs. Others are only male or female. Scallops reproduce by spawning - releasing eggs and sperm into the water. Once an egg is fertilized, the young scallop is planktonic, and then settles to the sea floor, attaching to an object with byssal threads. Most scallop species lose this byssus and become free-swimming as they grow.