The mollusc collection is one of the world's largest,
covering all groups of Recent and Tertiary molluscs.
Many of the specimens are dry shells, but there is
also a large collection of preserved molluscs.
The collections date from the 1860s and include marine,
terrestrial and freshwater molluscs.
|
|
INVERTEBRATES
1. Molluscs
Many of the animals that live inside shells are molluscs. They are commonly known as shellfish. Molluscs are an enormous and varied animal group, with over 120,000 species worldwide. Mollusc means soft bodied. The typical mollusc has a soft body, a muscular foot on which it moves and a hard shell made of calcium carbonate and other minerals extracted from seawater; but there are many variations.
On the shore, the group includes gastropods (snail-like molluscs) such as limpets, abalones, topshells, nerites, winkles, conches, whelks, cowries, and cone shells. These animals' soft bodies are surrounded by hard shells, which protect them. Gastropod means "stomach-foot". The animals appear to slide along on their bellies.
Some molluscs have two shells, or valves. They are called bivalves. These include cockles, mussels, scallops, clams, oysters, razorshells, and shipworms. Tusk shells, chitons, sea-slugs, squid, and octopuses also belong to the mollusc group. All bivalves live near the water. Their shells are opened and closed by strong muscles. The animal's soft body is inside the two valves. It is completely protected by the shells. The animal eats by drawing water inside its shell and trapping the tiny creatures that float in the water.
Other molluscs like abalone, have one shell. Molluscs move along on a large fleshy foot, carrying their shell wherever they go. They have a long tongue, or radula, with rows of tiny teeth that scrape food. Some animals with shells live on rocky shores. They fix themselves to the rocks. When the tide goes out, some of the animals shelter under seaweed or in rock pools.
Scallops are one of the few bivalves that swim. They move by flapping their shells together and squirting out water. They can swim backwards and forwards.
When molluscs die, their soft bodies rot away. The empty shells are often washed up on the beach. Many people collect seashells. It is easy to begin a collection, as most shells are easy to find. Some shells are very rare, only a few collectors find them.
1.1 Mussels
Mussels attach themselves to rocks with a thread. A special gland in their foot produces a thick liquid, which hardens into a thread called byssus. Mussels can grow new threads if they break.
1.2 Oysters
Oyster shells are lined with mother-of-pearl. If a grain of sand gets inside the shell, it hurts the oyster's soft body. So it covers the sand with mother-of-pearl. This makes a pearl. Pearls are valuable. Divers swim to the seabed to collect them. Oysters are good to eat. A strong muscle holds the oyster's two shells firmly together. To get at the flesh, the shells must be levered open with a knife.
Oysters are often eaten raw in their natural juices, straight from the shell. There are many species of oysters from different regions. The oyster is a filter feeder. It draws in a current of seawater, filters out tiny floating food particles and passes these into its digestive system, using tiny beating hairs called cilia. They are often farmed in special oyster beds. Young oysters or spats float about in the water. As they grow older, they find a hard surface to attach themselves to. The farmer scatter shells for the spats to rest on. When the oysters are fully grown, the farmer can collect them with a rake.
1.3 Abalone
Abalones, or ear shells, are known for the beautiful rainbow-sheen mother-of-pearl on the inside of the shell. These relatives of topshells and limpets graze on algae and are themselves eaten as a seafood delicacy, especially western North America and the South Pacific.
1.4 Chitons
Chitons or coat-of-mail shells, are common molluscs on many rocky shores, but are difficult to spot as they blend in with the rocks. This species is a mid-shore seaweed-grazer from the Indian Ocean. Its tiny teeth are capped with a hard, iron-containing substance that prevents them from becoming worn.
1.5 Topshells
Topshells, with their striped and spotted cone-shaped shells, are bright and familiar inhabitants of rock pools.
 Back To The Top
2. Crustaceans
Some of the most curious-looking creatures of the shore are crabs, prawns, and lobsters. They are members of a large and varied group of animals called the crustaceans. In the same way that insects swarm on land, so crustaceans teem in the sea. Both groups are arthropods or joint-legged animals.
Crustaceans usually have jointed limbs (up to 17 pairs in some species), two pairs of antennae, and a hard shell, or carapace that encloses and protects much of the body. However the animals themselves vary enormously. They range from microscopic creatures that make up a large part of the floating plankton (the "soup" that nourishes so many filter-feeding sea animals), to the giant spider crabs of Japan, which measure more than 3.5m (12ft) across the claw-tips.
Some of the most surprising members of the crustacean group are the barnacles (cirripeds). These animals begin life as tiny, free-swimming larvae. Some species then settle on the shore, cement their heads to the rock, grow hard plates around their bodies, and use their six pairs of feathery, jointed "legs" to kick food into their mouths! The crustaceans most familiar use are the decapods, which include shore creatures such as crabs, lobsters, crawfish, hermit crabs, prawns, and shrimps. Decapod means "10-legged), and most of these creatures have 10 main limbs. Four pairs are for walking or swimming, and there is one pair of manipulating pincers.
A shell also protects a crustacean's body. The shell is like a suit of armour. It is jointed so that the animal can move. Crustaceans have claws for breaking up food. Examples of crustaceans include lobster, crabs, shrimps and prawn.
2.1 Crabs
Crabs are crustaceans. A hard shell covers their head and body. Crabs have four pairs of walking legs. They move sideways along the shore. They can bury themselves rapidly in the sand. Many different crabs live by the sea. Most crabs are adept scavengers, picking up almost anything edible from the sea-bed with their pinchers.
Early astronomers saw a crab-like pattern of stars in the northern night sky and named it Cancer after the Latin word for a crab. Cancer is also the forth sign of the zodiac, with the Sun passing through from about 21 June to 22 July.
2.2 Lobsters
Lobsters live in the sea. Although they live in offshore waters, lobsters are occasionally found on the lower shore marooned in rock pools. Like other crustaceans, they have the characteristic hard and heavy carapace. Lobsters usually hide in crevices and holes during the day, emerging at night to feed on dead or dying prey. They crush prey with the larger front claw and pick off bits with the smaller one. They crawl across the seabed looking for food. They can swim backwards, by flapping their tails. They catch their prey with huge pinchers. As the lobster grows, it needs a bigger shell. It hides in a safe place and sheds its old shell. A new, larger shell is underneath. The new shell is soft but it soon hardens. If a lobster breaks a claw, it can grow another one next time it moults.
3. Other
3.1 Squid
The biggest molluscs are giant squids. They live in the deep sea. They have a thin shell inside their body, and fins to help them swim. Squids swim by forcing a jet of water through a siphon. Their long tentacles have suckers for catching prey.
Back To The Top
4. Aquatic Plants
4.1 Seaweed
The most obvious seaweeds on the shore are usually the large brown seaweeds known as wracks and kelps. Wracks are leathery strap-like seaweeds that grow in bands between the high- and low-tide marks. Some species have air bladders that keep the main body (the thallus) of the weed afloat as the waves come and go. The kelps have much broader blade-like fronds and tend to live around the low-water mark and below. Red seaweeds are generally smaller and prefer shady rock pools and deeper water beyond the kelp zone. They contain a red pigment, phycoerythrin, that masks out the green pigment chlorophyll, which is present in all plants. This is more efficient at using the dim light filtering through seawater than the fucoxanthin pigment of the brown seaweeds. This means that the reds are able to grow at greater depths than other seaweeds.
The holdfast habitat. Seaweeds do not have true roots. The gnarled, root-like structures of large brown seaweeds are called, appropriately, holdfasts. They hold tight to the rock and provide anchorage, like a tree's roots in the soil. Unlike true roots, the rootlets of a holdfast do not take up water or nutrients; instead these are absorbed through the whole surface of the seaweed. However, holdfasts do provide shelter on the shore. Just as trees protect a woodland's interior from wind, driving rain, and hot sun, so the leathery fronds and tough holdfasts of the low-shore kelp forests keep off the sun and lessen the force of waves and winds. Many smaller plants and numerous shore animals, such as crabs, fish, prawns, and molluscs, take advantage of the calmer conditions within the forests of brown seaweeds. During storms, weaker seaweeds are torn from the rocks. In the storm's aftermath, huge mounds of kelp are found on the shore, often with their inhabitants still clinging to the fronds.
4.2 Seaweed Salad
Sea lettuce, which looks a lot like the plant we eat in salads,, can grow in many different habitats - in the slightly salty water of estuaries, in seawater, and even in mildly polluted waters. This green seaweed is very common. It can be found attached to rocks, floating freely, or washed up on shore.
4.3 Sugar kelp
The sugar kelp or sugar wrack is a big brown seaweed of the low-water level and below. Its crinkly frond and wavy edges are distinctive, as is the sweet taste of the white powder that forms on its drying surface. It is eaten as a delicacy in the Far East.
Source:
1989 Dorling Kindersley Limited, London. Seashore
Back To The Top
|
|
