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Crabs.

Crabs are found all over the world, both on land and in water. In fact, scientists have counted more than 4400 species of crabs! Crabs are crustaceans (crus TAY shuns), like lobsters and shrimp. Most crustaceans have a soft body covered by a hard shell, or carapace (CARE uh pace). Crustaceans breathe through gills, just like fish. Crabs smell through their antennas.

Characteristics

Crabs come in many sizes. The smallest is the pea crab, which is only 1/2 inch wide. The largest is the Japanese spider crab, which can grow up to 12 feet across. That is twice as long as your bed! Crabs have 10 jointed legs on the sides of their bodies. They usually walk sideways. Some crabs have paddles on their back legs and can swim in all directions. Crabs are scavengers, which means they eat dead plants and animals. They use their claws to grab food. Some of their favorite foods are fish (dead or alive), clams, plankton, and seaweed. Land crabs like to eat leaves and rotting fruit. Crabs have excellent eyesight. Their eyes are on stalks, which they can raise or lower.

Survivors

Crabs have been around for millions of years, changing little from their original forms. Birds, fish, and octopuses like to eat crabs. So do people! Crabs, though, are great survivors. To protect themselves, they hide in mud or sand with just their eyestalks sticking out. Sometimes they put shells or bits of seaweed or sponge on their shells for camouflage. Crabs are also protected by their shells and powerful, pinching claws. If an enemy grabs its leg, a crab can break it off and speed away! Later, the leg will grow back! This is called regeneration.

A Crab's Life

Crabs hatch from eggs. A female blue crab may lay up to 2 million eggs at once! However, most of these will not make it to adulthood. After hatching, crabs' bodies go through many changes before they become adults. Crabs grow bigger, but their shells don't. They shed their old shells and grow brand-new, bigger ones. When the new shell is ready, the crab leaves its old shell. This is called molting. Are crabs "crabby," like grouchy people? Experts disagree about whether crabs are bad-tempered, but many crabs do fight when crowded together.

Background

Many of us are familiar with crabs because we've seen them on our dinner plate or perhaps in a tasty soup or as a crab cake. However, the well-known species of edible crabs are just a tiny fraction of all the various kinds of crabs in the world. Crabs are fascinating, diverse creatures found almost everywhere on Earth. There are more than 4400 different species of crab.

Crabs are a much-loved food throughout the world. The annual harvest of crabs is a multimillion dollar industry in the U.S. For many people, crabbing is a fiercely independent way of life, passed down from generation to generation.

One of the most important food crabs is the blue crab, found along the Atlantic coastline. Another is the Dungeness, caught along the Pacific coast of the U.S. King crabs, prized for their large, tasty legs, live in the north Pacific and Bering Sea. For stone crabs, caught in the coastal waters of Florida and Louisiana, only the claws are eaten.

Most crabs live in the sea, but some live in fresh or brackish (partly salty) water, and some on land. Still others divide their time between the land and water. Crabs are crustaceans, like lobsters and shrimp. Scientists have found fossils that show crab ancestors were on Earth almost 200 million years ago and have changed little from their original form.

What Makes It a Crab?

Crabs have 10 jointed legs, 4 antennas, and a hard outer shell, or carapace (CARE uh pace) covering a soft body. They usually walk sideways, because their legs are attached to the sides of their bodies. Swimming crabs generally have paddles on their back legs and can swim in all directions. All crabs have claws on their 2 front legs. They use them to grab and hold food, to crack open the hard shells of their prey, and to fight and defend themselves. Their antennas help them smell, taste, and sense vibrations.

Crabs' eyes are on stalks, which they can raise or lower into their sockets. They can also rotate their eyes to see almost directly behind them. Crabs' eyes are compound, made of many lenses, and their eyesight is excellent. Sometimes crabs bury themselves in sand, with just their eyes poking up, hiding from predators or waiting for a meal to pass by. Burrowing crabs have a special mouth structure which allows them to breathe while buried. Crabs breathe like fish, taking oxygen from the water through their gills, which are located under their shells. Land crabs can breathe air, but must return to the water to wet their gills. You can tell the sex of most crabs by looking at the abdomen, or "apron."

The size of crabs varies tremendously. Pea crabs may be just 1/2 inch wide. Meanwhile, the enormous Japanese spider crab may measure up to 12 feet from claw to claw!

With a varied diet and voracious appetites, crabs are scavengers, eating dead plants and animals. Among their favorite foods are fish (dead or alive), clams, plankton, and seaweed. Land crabs also enjoy dining on leaves and rotting fruit.

False Crabs

Some "crabs," like hermit and horseshoe crabs, aren't true crabs at all. Hermit crabs are not true crabs because they borrow their shells from dead marine animals such as periwinkles and whelks. Every so often, the hermit crab has to move to a "bigger house" when it outgrows its borrowed shell.

Unlike true crabs, horseshoe crabs have more than one pair of claws and lack jaws and antennas. Horseshoe crabs today are very similar to those living millions of years ago. For that reason, horseshoe crabs are sometimes called "living fossils." Scientists have been able to learn a lot about human eyesight from studying horseshoe crab eyes.

Life Cycle

Visual and auditory signals are especially important in the mating rituals of land crabs. Male fiddler crabs have elaborate courtship rituals for enticing females into their burrows. Water crabs use pheromones, or scents, to attract mates.

A female blue crab may lay up to 2 million eggs at a time! Only a few of these will survive to adulthood, however. When crab eggs hatch, tiny larvae called zoea emerge. Most zoea are just 1/100 inch wide. They do not look very much like adult crabs. The zoea feed on plankton (while larger plankton and fish feed on them!) They molt repeatedly and eventually become megalops, with very large eyes, a large abdomen, and long tails. Finally, the megalops become adult crabs.

In order to grow, crabs must molt. A new, larger shell has already grown underneath the old shell, but it is soft at first. Crabs are vulnerable and will hide during their soft shell stage, which lasts several days. Blue crab males will protect the female during this time. Right after the molt, the crab gulps water to make its body expand before the new shell hardens.

Crabs have some amazing abilities. One is called autotomy. If a predator grabs a crab's leg, or if it is injured or trapped, the crab can cast off its own claw or leg and escape. The leg or claw is broken off along a built-in weak spot, or breaking plane. To complete the process, the crab also has the ability to grow a new limb to replace the lost one! This is called regeneration. It takes many molts for a lost leg or claw to be completely regenerated.

Crab Products

When people eat blue crabs, they only consume about 10 to 15% of the crab. Rather than waste the remainder, researchers have found many uses for crab products. Crab parts are made into fish bait. The shells of crabs contain chitin (KITE in), a protein material similar to fingernails. Chitin is broken down into fibers and made into bandages. These bandages help skin grow better and speed the healing of wounds. They are often used on burn victims. Chitin is also spun into thread for sutures. It is often added to animal feed and used to enrich soil. Chitin has recently been marketed as a weight loss product, but its effectiveness has not been proven.

Future of Crabs

Crabs are remarkable survivors, having been on Earth for almost 200 million years. They protect themselves with their hard shells, powerful claws, and the ability to regenerate lost limbs. Many crabs also camouflage themselves, putting seashells, bits of sponge, or seaweed on their shells. Some crabs bury themselves in sand or mud, or hide among rocks and seaweed. Despite these defenses - and the fact that females produce vast numbers of eggs - scientists worry that crab populations may be declining, in some cases due to overfishing. For example, some experts predict that the Japanese spider crab may be extinct within a few decades. People are eating too many of them, including the egg-laying females.

Some fluctuations are seasonal. The number of crabs can greatly increase or decrease from year to year. Excessive rain can lower the salinity (salt) level of the water and kill crab larvae. Extremely cold temperatures in winter can kill dormant crabs. Unusually large numbers of predators can also affect crab populations.

Pollution harms crabs in many ways. Fertilizers used on lawns and farms run off into waterways, encouraging an overgrowth of algae. Too much algae depletes the oxygen in the water. It also keeps sunlight from reaching the aquatic grasses which crabs eat and use for shelter. Run-off of manure from chicken farms has been blamed for recent outbreaks of disease in East Coast waters. These diseases kill large numbers of fish, which crabs, in turn, rely on as a food source. Scientists are now studying the adverse effects of ozone depletion on phytoplankton, the basis of the food chain in all rivers, bays, and oceans. So far, results show that phytoplankton in some areas, including the Chesapeake Bay (home to large numbers of blue crabs), are doing better than others.

National science Education Standards

Unifying Concepts and Processes (K-8)

* Systems, order, and organization

* Evidence, models, and explanation

* Constancy, change, and measurement

* Evolution and equilibrium

* Form and function

Standard A: Science as Inquiry (K-8)

* Abilities necessary to do scientific inquiry

* Understanding about scientific inquiry

Standard B: Physical Science (K-4)

* Properties of objects and materials

* Position and motion of objects (5-8)

* Properties and changes of properties in matter

* Motions and forces

Standard C: Life Science (K-4)

* The characteristics of organisms

* Life cycle of organisms

* Organisms and environments (5-8)

* Structure and function in living systems

* Reproduction and heredity

* Regulation and behavior

* Populations and ecosystems

* Diversity and adaptations of organisms

Standard D: Earth and Space Science (K-4)

* Properties of earth materials (5-8)

* Structure of the earth system

Standard G: History and Nature of Science (5-8)

* Science as a human endeavor

Meet Some Amazing Crabs

Japanese spider crabs - The largest of all crabs, they can grow to be 12 feet from claw to claw. A single claw may be 6 feet long! Their bodies are small relative to the size of their legs. These crabs use the hairlike hooks on their bodies to attach bits of shell and seaweed as camouflage.

Blue crabs - They are one of the most important food crabs for humans and are sometimes eaten in their soft shell state. Many people think they are the tastiest crabs. The greatest concentration of blue crabs is in the Chesapeake Bay. They live up to 3 years.

Pea crabs - One of the smallest crabs, they may be just 1/2 inch wide. Female pea crabs sometimes live inside the shells of mussels, clams, and oysters, feeding on whatever their host eats.

Stone crabs - The claws of these crabs are prized for eating. Crabbers in Florida catch them, remove one claw, and throw the crab back to grow another claw.

Robber or coconut crabs - They climb trees to get coconuts, crack them with their claws, and eat the meat. They are not true crabs.

Fiddler crabs - Fiddler crabs live on land, burrowing in mud or sand or among mangrove tree roots. Males have one large claw, which they use to signal other fiddler crabs. Crabs from different beaches may not understand each other's "sign language."

Ghost crabs - These fast land crabs dig large burrows in sand. They can run 7 feet in 1 second!

Dungeness crabs - These crabs are found on the Pacific coast, from Alaska to San Francisco. They are large, weighing up to 3 pounds and measuring 10 inches across their shell. They have a long life span for a crab (up to 8 years.)

Arrow crabs - A type of spider crab, these crabs spread out their long legs in the ocean. They then eat the bits of dead animal and plant matter that stick to their legs.

Striped shore crabs - These crabs live on beaches in Oregon and California and hunt for food in and out of the water. Their bodies are about 2 inches across.

DID YOU KNOW??

A crab's legs are made up of rigid parts with flexible joints, so they can bend.

DID YOU KNOW??

The fast ghost crab runs on its tip-toes!

DID YOU KNOW??

Female blue crabs are said to "paint their fingernails" because their claw tips are red.

DID YOU KNOW??

Callinectus sapidus is the scientific name for the blue crab. It means "beautiful swimmer."

DID YOU KNOW?

Most crabs can't swim.

DID YOU KNOW??

A crab's legs are made up of rigid parts with flexible joints, so they can bend.

DID YOU KNOW??

Some male ghost crabs build sand pyramids to attract a mate.

DID YOU KNOW??

Callinecticus sapidus is the scientific name for the blue crab. It means "beautiful swimmer."

We suggest bringing a real crab or crab shell to class, if possible, so your students can examine it first-hand.

Vocabulary

Circle the things crabs like to eat. The words can go across, backwards, up, down, or diagonally.
S D Z B A I T V A H N V B L F
H S R F S E A W E E D Z H E P
R M N V R N O T K N A L P A S
I A E A A U K I I E P S S V Q
M L L B I F I S H E S D G E U
P C S S C L G T F L A Q G S I
D S M R O W S L A S Q A E V D

seaweed
plankton
eggs
bait
snails
clams
fish
leaves
worms
fruit
shrimp
eels
squid
Weeky Lab


Make your own bread roll crab!

You need: a kaiser (or other hard) roll, 5 large pipe cleaners (cut in half), 5 plastic straws (each cut in 8 pieces), 2 toothpicks, 2 raisins, 2 small binder or bulldog clips

Step 1: Slide 4 straw pieces onto a pipe cleaner. Bend 1 end of the pipe cleaner down to keep the straws from coming off. Push the other end of the pipe cleaner into the side of your roll. (See picture.) This is one of your crab's legs.

Step 2: Make 7 more legs and stick them into the roll. Put 4 legs on each side.

Step 3: Put 3 straw pieces on each of the last 2 pipe cleaners. Attach a binder clip to the end of each one. Stick the other ends of the pipe cleaners in the front of your roll. These are your crab's claws. (Bend all of your pipe cleaners.)

Step 4: Push a raisin onto the end of each toothpick. Stick the toothpicks in the top of your roll, near the front. These are your crab's eyes and eyestalks.

DID YOU KNOW??

The word crustacean comes from the Latin words "crusta" meaning shell and "acea" meaning group.

DID YOU KNOW??

Some "decorator" crabs trick their enemies by decorating themselves with shells and plants.

Bonus: Glue bits of tissue paper, sponges, and sequins on your roll to help disguise and protect your crab from enemies, just like decorator crabs.

Weekly Problem

Solve the problems to find out these crab facts.

Ghost crabs can run -- feet in one second.

(387 + 420) - 800 =

Dungeness crabs can live up to -- years.

(501 - 497) x 2 =

Crabs may molt more than -- times in their lives.

(27 x 7) - 169 =

A Blue crab can weigh -- pound.

2/10 + 3/10 = (reduce)

DID YOU KNOW??

Horseshoe crabs and hermit crabs are NOT really crabs.

DID YOU KNOW??

Crabs have eyes on long eyestalks. This lets them peep over things to check that everything is safe.

Writing for Science

The old science editor at 4KIDS-TV has just been fired for doing an awful job of researching their upcoming program on crabs.

Congratulations! You have been hired as the new, improved science editor. Your first job is to fix the mistakes in this story. Circle all the mistakes. Then write up your corrected crab report.

CRABS

There are less than 100 different species of crabs! All crabs have soft shells over their hard bodies. They have excellent eyesight. Some of their favorite foods are fish, clams, and plankton, but they will not eat anything that is dead. Crabs come in many sizes. The smallest crab is the tiny Japanese spider crab, no bigger than a nickel. Crabs have been on Earth for millions of years, and they have changed a lot from their original form. Crabs hatch from eggs. If a crab loses a leg, it can grow a new one? This is called molting.

DID YOU KNOW??

When a blue crab molts, it "backs out" of its old shell.

DID YOU KNOW??

The arrow crab has such long legs, it looks like it is walking on stilts.

DID YOU KNOW??

Coconut crabs climb palm trees to get coconuts to eat.

Challenge

Male fiddler crabs have one very large claw. They wave this claw to signal messages to nearby fiddler crabs. They also use it to fight other males and to attract females.

Play Fiddler Crab Charades!

Divide up into. teams. Quietly, decide on the crab words you want to use. Write them on slips of paper and put them in a bag. The words must have something to do with crabs, like a crab part, something crabs eat, or the name of a type of crab.

Now you are ready to play! Take turns picking words from another team's bag. You can use your body to give clues to your teammates, but no talking is allowed!

Bonus: Try giving clues using just one arm (your "claw") like fiddler crabs do!

DID YOU KNOW??

Crab shells contain chitin, which is used to make bandages.

DID YOU KNOW??

If a male fiddler crab's large front claw breaks off, it grows a small new one. Then its other front claw turns into the big one.

DID YOU KNOW??

Some ancient Egyptian coins had pictures of crabs on them.

Puzzle

Some female pea crabs live inside these.

1) Cross out all the consonants in Row C.

2) Cross out all the letters in Row B that come before the letter M in the alphabet.

3) Cross out all the vowels in Columns 1, 3, and 5.

4) Cross out all the letters h, f, and w.

5) To find the answer, circle the remaining letters. Write them, in order, in the spaces below.

DID YOU KNOW??

The pine crab lives in water that collects at the bottom of bromeliad plants that grow on tropical trees.

Level Pre-A

Main Concepts: Crabs have hard shells and 10 legs. They are many kinds of crabs.

Picture Activity

Ask your students what they see on the front page. WHY-FLY is looking at some crabs on the beach - (from left to right) a fiddler crab, a ghost crab, and a blue crab. Explain that there are many kinds of crabs. They have hard shells and 10 legs. Their hard shells protect them. Read what WHY-FLY is saying. Explain that some crabs swim and others walk. The ghost crab can run very fast. The fiddler crab has one very large claw for signaling to other fiddler crabs. The blue crab is a water crab and swims very well. Have them point out each crab. Ask if they have ever seen a crab.

Vocabulary

Go over the "sh" sound together. Have everyone put a finger to their lips and say "Shhh!" Read the sentences to them. Then have them trace over all the letters "sh." Have them say the "sh" words out loud.

Weekly Problem

Answers: The fiddler crab has the most legs - 10 (circle in red). The girl has the fewest legs - 2 (circle in purple). (The dog has 4 legs and the ant has 6.) Explain that all crabs have 10 legs. First go over the directions together and then have them color in the mini-crayons. Next have them count the legs on each one and circle the ones with the most legs and the fewest legs.

Storytelling

Crabs' eyes are on stalks. The stalks can go up, down, and all around. Explain that sometimes crabs will hide in mud or sand with just their eyes sticking out. This helps protect the crabs from their enemies. The buried crabs can easily see when an enemy or something to eat comes by. Crabs see very well, which helps them find food.

Challenge

Crabs' legs are on the sides of their bodies. This is why they walk sideways, but can swim in all directions. Have them try walking like a crab on their hands and knees. They can try crawling forwards and then sideways. Which was harder for them? (It is harder for us to crawl sideways, because our legs are not on the sides of our bodies.) If space permits indoors, or the weather is nice outdoors, plan a class crab relay race. Have them alternate crawling forwards and sideways or have teams try one method and then the other.

Weekly Lab

You need: scissors, paper plates, staplers or tape, pipe cleaners, mini-marshmallows, paper fasteners, crayons (optional - a hole punch). This lab will help reinforce the parts of a crab's body - shell, legs, and claws. Explain that a crab's legs are jointed, so they can bend. Ask them if their legs can bend. Have your students fold their plates in half. Then have them cut out the side legs, the front legs, and the claws. They can tape or staple the side legs to the sides of their plates. Then have them tape the rest of the plate together, leaving an open space in front. Have them insert paper fasteners in the red dots on the 2 front legs and the claws, and attach them together. (You can use a hole punch, if needed, to make the holes.) Next have them attach the 2 front legs to the front of the paper plate with paper fasteners - at the blue dots. Finally, have them put their mini-marshmallows (or gum drops may also be used) on the ends of the pipe cleaners. They will stick the pipe cleaners into the front of their plates. They may need to use more tape or staples to secure them. These will be their crab's eyes and eyestalks. Have them color in their crab's shell. Encourage them to be creative - most often, crabs are green, blue, or gray, but some are purple, red, pink, yellow, orange, or spotted.

DID YOU KNOW??

The fast ghost crab runs on its tip-toes!

Level A

Main Concepts: Crabs have hard shells and 10 legs. There are many kinds of crabs. They may live on land or in water.

Picture Activity

See TN Level Pre-A - PICTURE ACTIVITY.

Vocabulary

Go over the "sh" sound together. Have everyone put a finger to their lips and say "Shhh!" Have them write "sh" in the blank spaces. Read the sentences and have them say the "sh" words out loud. Can they think of any more words that begin with the "sh" sound?

Weekly Problem

Answers: dog - 4, fiddler crab - 10, girl - 2, ant - 6. The fiddler crab has the most legs (circle in red). The girl has the fewest legs (circle in purple), Explain that all crabs have 10 legs. First read the directions and then have them color in the mini-crayons. Next have them count the legs on each one, fill-in the boxes, and circle the ones with the most and the fewest legs.

Writing for Science

Explain that crabs' eyes are on stalks that can go up, down, and around. Crabs sometimes hide in mud or sand with just their eyes peeking out. This protects them from their enemies. The buried crabs can easily see when an enemy or something to eat comes by. Crabs see very well, which helps them find food. Encourage them to use their imaginations when creating their stories.

Challenge

Crabs' legs are on the sides of their bodies. This is why they walk sideways, but can swim in all directions. Have them try walking like a crab on their hands and knees. They can try crawling forwards and sideways. Which was harder for them? (It is harder for us to crawl sideways, because our legs are not on the sides of our bodies.) If space permits indoors, or the weather is nice outdoors, plan a class crab relay race. Have them alternate crawling forwards and sideways or have teams try one method and then the other.

Weekly Lab

See TN Level Pre-A-WEEKLY LAB. In addition, at this level, they will be making 2-part claws that open and close. Have them use paper fasteners to attach each of the claw pieces to each other (at the yellow dots).

DID YOU KNOW??

The word crustacean comes from the Latin words "crusta" meaning shell and "acea" meaning group.

DID YOU KNOW??

Some ancient Egyptian coins had pictures of crabs on them.

Level B

Main Concepts: There are many kinds of crabs. Some live in water and some on land. Crabs have hard shells and 10 legs. Some crabs have paddles for swimming. The Japanese spider crab on the front page is twice as long as a bed. The pea crab is as tiny as a pea.

Vocabulary

Answers: fish, shells, shore, shirt. Go over the pictures together first. Have them think of other words with the "sh" sound.

Weekly Problem

Answers: 1) 7, 14 2) 12.

Writing for Science

Explain that crabs' eyes are on stalks. The stalks can move up, down, and all around. Sometimes crabs hide in mud or sand with just their eyes sticking out. This helps protect them from their enemies. The buried crabs can easily see when an enemy or something to eat comes by. Crabs see very well, which helps them find food. Encourage your students to think of different situations at home, school, and play where they could benefit from having their eyes on stalks.

Challenge

Crabs' legs are on the sides of their bodies. This is why they walk sideways, but can swim in all directions. Have them try walking like a crab on their hands and knees. They can try crawling forwards and then sideways. Which was harder for them? (It is harder for us to crawl sideways, because our legs are not on the sides of our bodies.) If space permits indoors, or the weather is nice outdoors, plan a class crab relay race. Have them alternate crawling forwards and sideways or have teams try one method and then the other. Have them switch, and try again. Which way did they prefer?

Weekly Lab

This lab will help reinforce the parts of a crab's body - shell, legs, and claws. Explain that a crab's legs are jointed, so they can bend. You may use gum drops instead of marshmallows for the crab's eyes. You may need to use tape or staples to securely hold the pipe cleaner eyestalks in place. Encourage your students to be creative when coloring their crabs' shells - most often, crabs are green, blue, or gray, but some are purple, red, pink, yellow, orange, or spotted. Some crabs put small shells and bits of seaweed on their shells to help camouflage themselves.

Level C

Main Concepts: There are thousands of kinds of crabs. They can protect themselves from enemies in many ways. Crabs molt when they get too big for their shells.

Vocabulary

Answers: The 2 missing consonants are "s" and "I." 1) shell 2) stalks 3) claws 4) paddles.

Weekly Lab

For this lab, you can use any type of hard roll - round or oval shapes work well (e.g., Kaiser rolls or small baguettes.) Mini-marshmallows or gum drops can be used instead of raisins for eyes. The binder or bulldog clips are a nice feature to add, because they illustrate the strong gripping power of a crab's claws. You can also have them construct 2 part claws, made out of cardboard. Put the parts together with paper fasteners, so they can open and close, and attach them to the ends of the 2 front pipe cleaners. They can also use large, open paper clips to represent the claws.

Weekly Problem

Answers: Crabby ate 17 pieces of food, Gabby ate 27 pieces, Tabby ate 15 pieces, and Abby ate 30 pieces. Abby ate the most.

Writing for Science

Discuss the different ways crabs protect themselves. They have hard shells and claws for pinching. They can hide in mud or sand with just their eyes sticking out. Some crabs camouflage themselves with bits of sponge, shells, and seaweed. The male fiddler crab even has one huge front claw that it can use to fight with other males. Have your students imagine some special ways a "Supercrab" could protect itself. Then have them write their stories.

Challenge

See TN Level B - CHALLENGE. In addition, have them name some other animals that have legs on the sides of their bodies (e.g., spiders, lobsters, lizards, etc.).

Puzzle

Answers: ACROSS - bait, seaweed, fish BACKWARDS - plankton, worms UP - clams, eggs DOWN - shrimp, eels, leaves, squid. Crabs are scavengers - they eat dead plants and animals. (They also eat live plants and fish.) Ask if your students have ever gone crabbing. What did they use for bait?

DID YOU KNOW??

Soldier crabs walk forwards, not sideways, like other crabs.

Level D

Main Concepts: There are thousands of kinds of crabs. Crabs are crustaceans. They protect themselves from predators in many ways. Crabs molt when they get too big for their shells.

Vocabulary

Answers: ACROSS - bait, seaweed, fish BACKWARDS - plankton, worms UP - clams, eggs DOWN - shrimp, eels, leaves, squid. Crabs are scavengers - they eat dead plants and animals. (They also eat live plants and fish.) Ask if your students have ever gone crabbing. What did they use for bait?

Weekly Lab

See TN Level C - WEEKLY LAB. In addition, for the bonus, have your students glue bits of sponges, tissue paper, sequins, or small shells on their crabs. This is similar to how decorator crabs "disguise" themselves from their enemies.

Weekly Problem

Answers: 1) 7 2) 8 3) 20.

Writing for Science

See TN Level C - WRITING FOR SCIENCE.

Challenge

Fiddler crabs have one very large claw that they use to signal to other fiddler crabs. Scientists have found that fiddler crabs living on one beach may not be able to understand the signals of those on another beach. Play this game like regular Charades, but use only crab-related words. You might want to review Charades signals such as "sounds like," "short word," etc.

Puzzle

Answer: oysters. (The o will be left in Row A. The y, s, and t will be in Row B, the e in Row D, the r in Row F, and the s in Row G.) Female pea crabs are no more than 1/2 inch wide, and sometimes live inside the shells of live oysters. These tiny crabs feed on whatever the oyster eats.

Level E

Main Concepts: There are more than 4400 species of crabs. They are crustaceans and have many ways of protecting themselves. Crabs molt when they get too big for their shells. They can regenerate lost limbs.

Vocabulary

Answers: ACROSS - bait, seaweed, fish BACKWARD - plankton, worms UP - clams, eggs DOWN - shrimp, eels, leaves, squid DIAGONALLY - snails, fruit. Crabs are scavengers - they eat dead animals and plants (as well as live food). Have your students ever gone crabbing? What did they use for bait?

Weekly Lab

For this lab, you can use any type of hard roll. Round or oval shapes work well (e.g., a Kaiser roll or a small baguette.) Mini-marshmallows or gum drops can be used instead of raisins. The binder or bulldog clips are a nice feature to add, because they illustrate the strong gripping power of a crab's claws. As an alternative, they can construct 2 part claws, made out of cardboard. Put the parts together with paper fasteners, so they can open and close, and attach them to the ends of the 2 front pipe cleaners. They can also use large, open paper clips to represent the claws. In addition, for the bonus, have your students glue bits of sponges, tissue paper, sequins, or small shells on their crabs. This is similar to how decorator crabs "disguise" or camouflage themselves to hide from their enemies.

Weekly Problem

Answers: 1) 7 2) 8 3) 20 4) 1/2.

Writing for Science

Answers: The mistakes are:

There are less than 100 species of crabs, crabs have soft shells over hard bodies, they will not eat anything dead, the smallest crab is the Japanese spider crab, they have changed a lot from their original form, and growing a new leg is called molting. The correct information is: there are more than 4400 species of crabs, crabs have hard shells over soft bodies, they do eat dead things, the Pea crab is the smallest crab, crabs have not changed much, and growing a new leg is called regeneration.

Challenge

See TN Level D - CHALLENGE. As a bonus, let your students try giving clues with just one "claw"!

Puzzle

Answer: oysters. (The o will be left in Row A. The y, s, and t will be in Row B, the e in Row D, the r in Row F, and the s in Row G.) Female pea crabs are no more than 1/2 inch wide, and sometimes live inside the shells of live oysters. These tiny crabs feed on whatever the oyster eats.

DID YOU KNOW??

The pine crab lives in water that collects at the bottom of bromeliad plants that grow on tropical trees.

Level F

Main Concepts: There are more than 4400 species of crabs, living throughout the world, on land and in water. Crabs are crustaceans. They have many methods of self-protection. Crabs molt when they get too big for their shells. They can regenerate lost limbs.

Weekly Lab

Lab A: See TN Level E - WEEKLY LAB. Lab B: Explain that the populations of water crabs often vary greatly from year to year. One reason for this is that, after hatching, crabs are very sensitive to the water's salinity levels (the amount of salt in the water). Salinity levels vary depending on how much rainfall there is. In this lab, your students will find that the pen cap rises in the water as more salt is added. Fresh water is less dense than salt water. As the salt content increases, the water gets denser and has greater buoyancy, which lifts the cap higher in the water. A scientist studying the health of crabs would use a hydrometer to measure the water's salinity.

Weekly Problem

Answers: 1) 7 2) 8 3) 20 4) 1/2.

Writing for Science

See TN Level E - WRITING FOR SCIENCE.

Challenge

Answers: ACROSS - bait, seaweed, fish DOWN - shrimp, eels, leaves, squid BACKWARDS - plankton, worms UP - clams, eggs DIAGONALLY - snails, fruit. Crabs are scavengers - they eat dead animals and plants. (They also eat live food) Ask if your students have ever gone crabbing. What did they use for bait?

Puzzle

Answer: oysters. (The o will be left in Row A, The y, s, and t will be in Row B, the e in Row D, the r in Row F, and the s in Row G.) Female pea crabs are no more than 1/2 inch wide, and sometimes live inside the shells of live oysters. These tiny crabs feed on whatever the oyster eats.

DID YOU KNOW??

Female blue crabs are said to "paint their fingernails" because their claw tips are red.

DID YOU KNOW??

When a blue crab molts, it "backs out" of its old shell.

We wish to thank Prof. Fred Wheaton, Chairman, Dept. of Biological Resources Engineering, at University of Maryland, College Park, for his kind assistance.

Helpful Sources for Planning Your Science Weekly Classroom Activities

Recommended Resources

* Bailey, Jill. The Life Cycle of a Crab. New York: The Bookwright Press, 1990

* Cooper, Jason. Crabs. Vero Beach, FL: Rourke Publications, 1996

* Day, Nancy. The Horseshoe Crab. New York: Dillon Press, 1992

* Hollenbeck, Kathleen M. Dancing on the Sand - A Story of an Atlantic Blue Crab. Washington, DC: Smithsonian Institution, 1999

* Johnson, Sylvia. Hermit Crabs. Minneapolis: Lerner Publications Company, 1989

* Kite, Patricia. Down In the Sea: The Crab. Morton Grove, IL: Albert Whitman and Company, 1994

* Stefoff, Rebecca. Crab, New York: Benchmark Books, 1998

Internet Resources

Blue crabs - http://www.blue-crab.net http://www.dnr.state.md.us/fisheries/fishingreport/blucrbft.htm http://www.vims.edu/adv/ed/crab/anatomy.html

Pea crabs - http://brandon.ittralee.ie/research/Mary.htm

Japanese spider crabs - http://www.vt360.com/aquarium/tour3.htm

True crabs, false crabs, and hermit crabs - http://www.mov.vic.gov.au/crust/hermbiol.html

Lots of crab pics - http://www.tropicabelize.com/Restaurant/Crabs/Crabs%20&%20Lobsters.htm

Materials Needed for Issue 3 - Secret Codes

Pre-A - white crayons, water-soluble markers, white paper, mirrors (optional - lemon juice, Q-tips, lamps)

A - red and yellow construction paper, clear tape, scissors, paper towel rolls, paper clips (optional - white crayons, water-soluble markers, white paper)

B - red and yellow construction paper, clear tape, scissors, paper towel rolls, paper clips, mirrors

C - scissors, paper fasteners, paper clips

D - scissors, paper fasteners, paper clips (optional - construction paper, white paper)

E, F - scissors, paper fasteners, paper clips

We wish to thank Prof. Fred Wheaton, Chairman, Dept. of Biological Resources Engineering, at University of Maryland, College Park, for his kind assistance.
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Title Annotation:Facts, lessons and activities re. the crab
Publication:Science Weekly
Date:Sep 15, 2000
Words:6442
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