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Table of Contents
Crabs are decapod crustaceans with very short tails, are covered with a thick shell or exoskeleton, and are armed with a single pair of claws. There are over 6,793 species of crab spread across the oceans, freshwater, and even on land.
See the fact file below for more information on the Crabs, or you can download our 30-page Frog worksheet pack to utilize within the classroom or home environment.
Key Facts & Information
ORIGIN OF CRABS
- Crabs are one of the most ancient living species, with ancestors dating back more than 400 million years.
- It is said that crabs were even present 200 million years before the dinosaurs. Scientists say the prehistoric crab, which dates back 95 million years, defies all crab characteristics.
- The earliest unambiguous crab fossils are from the Early Jurassic, with Eocarcinus from the early Pliensbachian of Britain, which most likely represents a stem-group lineage because it lacks several key morphological characteristics that distinguish modern crabs.
ANATOMY
- Crabs have a segmented body that can split into two parts: the cephalothorax, the head and chest, and the abdomen.
- The crab’s body is covered in an exoskeleton, and it has a pair of pincers. Crabs typically have a flat body with their head and thorax connected beneath the carapace.
- Each of a crab’s three pairs of legs ends in a large claw. The scientific name for crab claws is chelipeds. These claws function to hold and pick up food, attack predators, and protect themselves from harm. Most crabs have both a cutting and a crushing claw.
- Antenna, or antennule, is the scientific name for a crab’s small whiskers. They allow the crab to interact with its environment through touch and chemoreception, as well as carry the chemical reaction sensor, which aids crabs in food discrimination. A crab has three pairs of antennules.
- The uropods are the posterior appendages found in almost all crustaceans and crabs. They are usually the last section of the body before the anus part. They aid in the crab’s movement. The anus part’s appendages are known as caudal rami.
- Crabs’ eyes are housed in independently movable and adjustable eye stalks. Crabs’ compound eyes make it difficult for them to focus, but their eyes are sensitive enough to sense UV rays and detect even the smallest movements.
- Despite their ability to regenerate their lost claws and legs, they cannot regenerate their lost eye.
- Crab legs are also called periods. They typically have five pairs of legs. The last four pairs are commonly used to sense the environment and walk, but because they are flattened, some aquatic crabs use the last pair to push through the water and help them move quickly. Crabs walk sideways because their legs join at the side of the body and the joints point upwards.
LIFE CYCLE
- Crabs go through many stages of development before becoming adults. In some early stages of development, crabs do not resemble crabs at all.
- They become more crabby as they grow older, similar to how frogs change from tadpoles to frogs.
- After a successful mating between two adult crabs, the eggs are released into the female’s abdomen, below the tail flap, and secured with a sticky material.
- They are safe in this location during embryonic development. Females carrying eggs are referred to as “berried” because the eggs resemble round berries.
- When the larvae have finished developing, the female releases them into the water, where they become part of the plankton. The tiny zoea larvae can float and enjoy the benefits of water currents because they are free-swimming.
- They have a spine, which likely reduces predation by larger animals. Most species’ zoea must find food, but some crabs provide enough yolk in their eggs for the larval stages to survive.
- The Zoeae will eventually develop into what we call megalopa, depending on the water conditions. The warmer the water, the faster crabs progress through their larval stages. As the crab progresses to the Megalopa stage, it begins to resemble a crab. It’s about 1 mm in size at this point.
- Before changing into a megalopa stage, which mirrors an adult crab except for the abdomen (tail) sticking out behind, each species has a specific number of zoeal stages separated by molts.
- The crab becomes a juvenile after one more molt, having to live on the bottom instead of floating in the water. This final molt, from megalopa to juvenile, is crucial, and it must occur in a habitat suitable for the juvenile’s survival.
HABITAT
- Crabs are aquatic animals, although they can also be found on the ground and, in some cases, some species of crabs, like the coconut crabs, climb palm trees. When they stay on land, they commonly dig deep holes in search of water.
- The exact location depends on the species, because they can be found in estuaries and coral reefs. Some crabs only live in subtidal zones, which indicates they live in a constantly submerged estuarine system.
- Other crabs can be found in the intertidal zone, which is defined as the region between the high and low tide points.
- Crabs of various types live in cold saltwater regions, warm sea areas, bodies of freshwater, and on land. Snow crabs, for example, live in the cold waters around Alaska, Greenland, Siberia, and Japan.
CONSERVATION
- Although many factors, such as increased predation of nests and adults, habitat loss and degradation, road mortality, commercial harvest for human food consumption, and mortality as bycatch in crab traps, have been linked to crab population declines, few studies have provided evidence linking these agents to population declines.
- There are several ways to prevent the population of some crab species from declining, including: Water quality measures, underwater grass restoration, and proper fishery management will all help to protect and sustain crab populations.
- Conducting a study to gather information about the ecological and biological characteristics of the crab; spreading awareness and capacities of local communities; and developing a co-management model to protect and harvest local natural resources sustainably could also help in preventing the endangerment of crab species.
Crab Worksheets
This fantastic bundle includes everything you need to know about Crabs across 30 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about Crabs, decapod crustaceans covered with thick shells and armed with a single pair of claws.
Complete list of included worksheets
- CRAB FACTS
- Vocabulary Aid
- THE ANCIENT CRABS
- Anatomy of a Crab
- Life of a Crab
- CRABS OF THE SEASHORE
- Crab Mentality
- Crab Coloring
- OCEANIC CRABS
- Crab Find
- LAND CRABS
- Yummy Crabs
- DEEP SEA CRABS
- LIVING IN THE DEEP
- Crab around the World
- The Crab Nebula
- THE SYMBOLIC CRAB
- Reflection
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Link will appear as Crab Facts & Worksheets: https://kidskonnect.com - KidsKonnect, March 8, 2017
Use With Any Curriculum
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