Chapter V - Wonder World Under Water V [Animals with jointed Limbs] [This book has been distributed into different chapter for easier access. Picture shown - are not part of the book.] Just as insects dominate the land, having the largest population and variety, their relatives the Crustacean dominate the waters. Like worms, their bodies are segmented but the number of joints is far fewer. Their legs are jointed and their bodies are encased in hard armour made of chitin-a substance similar to the horn of cattle or our fingernails. They do not grow steadily, for the tough outer casing restricts expansion. They remain of the same size for many weeks or months. One fine day, their skin splits, and a soft animal come out. It drinks a lot of water and absorbs the lime from the water and starts building a new outer shell. When the new skin is soft, the body suddenly increases in size, but, in a few days the shell will have hardened, and no further growth will take place until the next time the skin splits. This process of throwing off the body-shell is known as moulting. Many crustaceans can break off their limbs at will. The break occurs at a particular place, where a blood vessel gets squeezed to prevent bleeding. If an enemy catches a crustacean by a leg, this will break and remain behind with the enemy while the crustacean escape. A new limb will grow in its place. Among the most numerous animals in the sea the copepods. Small in size, only a few millimeters long, they are the grazers of the sea, like sheep or goats on land. They feed on the small plant life drifting in the water and, in turn, serve as food for larger animals and fish. They cling to the skin or gills and feed on blood and body fluids. Certain kinds of copepods are also found in fresh water. As numerous as the copepods are the water fleas. Mostly found in fresh water, they can survive even if the water dries up. The female lays eggs but does not require mating with a male. The female dies when the water dries up, but the eggs remain in the bottom soil and hatch when rain fills the pond again. This characteristic of resistant eggs is also found in fairy shrimps. These are prettily colored and live in small, temporary puddles of fresh water. They swim on their back with their numerous legs. They die when the water dries up, but just before this happens they lay resistant eggs. A similar creature, the brine shrimp, is found in saltpans where seawater is allowed to dry with the sun's heat to form salt. They can tolerate a very high salt content in the water in which they live. Their eggs can be dried and kept for many years. When the eggs are put into salt-water, they hatch in a day. Seed shrimps and clam shrimps, like oysters, have their bodies enclosed between two valves. Tadpole shrimps also have a hard, flat shell covering part of their bodies; they look like miniature horseshoe crabs. Fish lice have flattened, horseshoe-shaped bodies. They grow up to a centimeter and are parasites living on fish. Opossum shrimps have a pouch-like organ below the belly where eggs are held. Aquatic sow bugs are found on sandy beaches. A few of them are parasites living on fish and prawns. The isopod lives inside a gill-chamber of the prawn. To accommodate the parasite, the shell of the prawn gets swollen over that gill-chamber. They have their bodies depressed (flattened from above, downwards). One kind of sow bug is peculiar. When young, a male and a female enter the hollow body of the sponge called Venus's Flower Basket and live there. Soon they grow so big that they cannot come out and have to spend their whole lives inside. The Japanese give a present of a sponge containing the two prisoners to a newly married couple, as a symbol of happy married life! The sow bug's cousins, called side swimmers or scuds, look similar to them but have their bodies compressed (flattened from side to side), with the result that they cannot walk erect but fall over on one side. The allied skeleton shrimps are so slim that they appear as if starving. Hanging on to branched polype colonies or seaweeds, they sway to and fro with their legs held in an attitude of prayer. Walking along stone or concrete jetties, you might see small Volcano-like shells opening at the top. When they are submerged at high tide, you will notice that the flap-like lid opens and a feathery appendage comes out and goes in repeatedly. These are acorn barnacles, and though they live inside a limy shell, they are not snails but crustaceans. While the majority are only a few millimeters across, a few grow to over 5 cm. Some acorn barnacles grow on the shells of turtles and even on whales. Their cousins are the goose barnacles-so called because people once believed that geese were born from them. They have a leathery stalk enlarging into a flattened body covered by a few flat, limy plates. They usually live on floating pieces of wood, but I have also seen them on glass bottles and even on rubber slippers floating in the sea. Some live attached to sea snakes. The more highly evolved crustaceans have ten legs. They compromise the prawns, lobsters and crabs, and all are good to eat. Prawns have a long snout, with saw-like teeth, between the eyes. In addition to the five pairs of walking legs, they have swimming paddles on the lower side of the abdomen. The eyes are carried on the tips of long stalks, and each eye has many prism-like components, each forming a separate image. When alarmed, the prawns shoot backwards to escape danger. They are very particular about their personal cleanliness. The pistol shrimp can make a loud noise by snapping the thumb of its large claw against the palm. If you stand on the seashore, you will often hear their clicks. The cleaner shrimp is like a doctor to sick fish. It is transparent and selects a stone for its "clinic". Fish with parasites or wounds visit the clinic and allow the cleaner shrimp to climb onto their bodies, where it eats parasites and pieces of dead skin around wounds. Lobsters look somewhat like prawns, but grow larger, are more colorful, and have their outer shells hardened by lime. Their eggs remain attached to the swimming paddles for a few weeks while the babies form inside the eggs. Baby lobsters look very different from the adult, having a flat, leaf-like, transparent body with long legs. Lobsters walk on the sea bottom but can swim backward for short distances by flapping their abdomens. Crabs have very small abdomens, which are tucked under the body. Their sex can be easily made out by turning the crab over. The male has narrow, V-shaped abdomens, but in the female it is much wider. Crabs too carry their eggs tucked under their bodies, but their babies very different from those of lobsters, having long spines on their heads and noses. In walking crabs, all the legs ends in pointed tips, but in swimming crabs, the tips of the last pair are flattened to act as swimming paddles. In all crabs, the first pair of legs is modified to form claws, and in many crabs these claws are much larger in the male. In the Christ crab, there is a natural design of a crucifix in the center of the body, flanked on either side by an angel with flowing wings, Spider crabs have very long legs, and many of them have numerous spines. Some spider crabs break off pieces of sponge or seaweed and stick them on their spines, and look like a veritable walking garden. Thus their enemies cannot detect them. Others carry a large piece of sponge or the valve of a calm over their backs. Pea crabs enter the shells of claws or oysters when young and spend their enemies and eat the food collected by the claw, and the male visits her only to mate. The male fiddler crab has one of its two claws bigger than its body. It digs a burrow in the sand and waits at the entrance. When a female fiddler crab (which has small claws) passes nearby, he waves his claw frantically as if inviting her in. If she accepts his invitation, he leads her into his burrow where they mate. Two males encountering each other will wave their big claws threateningly, and sometimes a fight ensues. If a male loses his large claw is replaced by a small one. Sometimes you will see a crab with a soft, jelly-like mass between its main body and abdomen. This is a crustacean parasite, which spreads a network of tubes inside the crab's body. A peculiarity of this parasite is that if it attacks a male, the crab will change its sex and turn into a female! The whole body of lobsters and crabs is encased in a thick armour-like shell. In hermit crabs, the front part of the body is so protected, but the abdomen is soft and, therefore, vulnerable. To protect its belly, the hermit crab tucks it inside an empty snail shell and carries the shell wherever it goes. Since the snail shell is coiled, the hermit crab grows too big for its snail shell, it discards the shell and over a shell. Some hermit crabs place a sea anemone over their snail shell home. The sea anemone gives it protection against its enemies and, in turn, gets a free ride and bits of food when the hermit crab feeds. The robber crab is a giant cousin of the hermit crab, but lives most of the time on land. It can climb trees, and its powerful claws easily break a coconut, the inside of which it eats. Its abdomen however, is quite hard, so it does not require to be protected inside a snail shell. This is fortunate for the robber crab, for where would it find a snail shell big enough to accommodate its belly? Robber crabs are extremely rare, and are found, in India, only on one of the Andaman Islands. The mantis shrimp has a short head and chest, and a long abdomen. Its claws are held close to the body, as with the praying mantis, but they can suddenly shoot out to catch prey. These shrimps are as abundant as prawns in the sea, but are not eaten because of their small size and thick shell. The horseshoe crab is not a crab, but related to the spiders. Its name comes from the shape of the plate covering its body. This covers the body and legs, leaving only a long, spike-like tail exposed. It grows to 60 cm, and is found at a few places on the shores of Bay of Bengal. Sea spiders are tiny creatures with very small bodies and long legs. The body is so small that parts of the liver and stomach are inside the legs. Continue to Chapter VI - Wonder World Under Water VI [Snails, Clams and Cuttlefish]