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Arthropods: Insects, Spiders, Scorpions, Shrimp, Crabs, and More

Updated on September 25, 2014
Caterpillar
Caterpillar | Source

The Characteristics of Arthropods

Arthropods are invertebrate animals that have jointed appendages that can bend, exoskeletons to protect their bodies, and segmented bodies.

Insects, spiders, scorpions, mites, centipedes, millipedes, crayfish, lobster, shrimp, crabs, barnacles, and many other type of animals are all arthropods.

The cute little caterpillar to the right is an arthropod. He has an exoskeleton that he'll quickly grow out of, jointed legs on his thorax, and a segmented body.

On this page, I'll tell you about the various characteristics of arthropods and show you some arthropods too. Don't miss the video about compound eyes! You may be surprised at how an animal with compound eyes sees!


Types of Arthropods

Arachnids

(including spiders, scorpions, and mites),

Insects,

Millipedes,

Centipedes,

Crustaceans

(including crayfish, crabs, lobsters, shrimp, and even barnacles)

A Variety of Types of Arthropods

Arthropods
Arthropods | Source

Arthropods shown above:

Top left:. Fossil of a trilobite (from 400 million years ago)

Top right: Sea Scorpion

Middle left: Scorpion

Middle right: Blue crab

Bottom left: Centipede with eggs

Bottom right: Swallowtail butterfly

Arthropods include:

  • Arachnids (including spiders, scorpions, and mites)
  • Insects (including beetles, termites, Luna Moths, Walking Stick insects, etc.)
  • Millipedes and Centipedes
  • Crustaceans (including crayfish, crabs, lobsters, shrimp, and even barnacles)

What makes an arthropod an arthropod? - Arthropoda = "Joint Foot"

Crab
Crab | Source

  • One of the main characteristics of arthropods are their jointed appendages. The legs, antennae and mouthpieces are all appendages that have joints and thus can bend.

Lobster
Lobster | Source

Segmentation

- Arthropods have segmented bodies.

  • Another key feature of arthropods is segmentation.

    Segmentation means body sections that repeat over and over, such as in the lobster shown here. Segmentation only occurs during the larval stage (and not the adult stage) in some arthropods. For example caterpillars have segmented bodies, but butterflies don't.




Snake skin
Snake skin | Source

Exoskeleteon and molting

  • Arthropods have an exoskeleton. This is a "skeleton" made mostly of chitin on the outside of their bodies. It both protects the arthropods' body and also helps prevent the arthropod from drying out. In order to allow the arthropod to be able to move, the exoskeleton is thin at the joints of appendages.
  • When they outgrow their exoskeleton, arthropods molt. Molting means climbing out of one's old exoskeleton after having grown a new one underneath. Although the new exoskeleton is soft at first, it soon becomes hard.

Shown here is a picture of a snake skin. When the snake grew too large for his current skin, he shed it. Although snakes molt, they are NOT arthropods. Snakes are reptiles.


Watch this Cicada molting. This is a very short movie of a cicada coming out of his skin. Unlike the snake above, a cicada is an arthropod!

Compound Eyes

A closeup of the face and eyes of a Blue Bottle Fly
A closeup of the face and eyes of a Blue Bottle Fly | Source
Compound eye of an Antarctic krill.
Compound eye of an Antarctic krill. | Source

Many arthropods have compound eyes made up of many smaller "eyes."

  • Many arthopods have compound eyes. Compound eyes are made up of many individual units. The brain receive information from all of the individual units and puts them together into a whole scene. Arthropods with compound eyes can't focus on things that are far away as well as we can, but they can detect motion much easier than we can. This makes sense for an arthopod, as being able to see things that are moving nearby is much more important to the safety of an arthopod than being able to see great distances!


    Shown here is the compound eye of an Antarctic krill.


Fascinating video on Seeing With A Compound Eye!

Simple and compound eyes on a wasp
Simple and compound eyes on a wasp | Source

Simple Eyes

  • Many insects have simple eyes, in addition to compound eyes. Simple eyes can detect light. In some insects, simple eyes can allow the insect to see the horizon. Being able to see the horizon gives the insect guidance in flight.

Shown here are the simple and Compound Eyes on a Wasp (The simple eyes are circled.)

Simple eyes on a spider
Simple eyes on a spider | Source

  • Spiders have simple eyes, but no compound eyes. Each pair of simple eyes in a spider is adapted to a specific task.

Parts of an arthropod's body
Parts of an arthropod's body | Source

Most arthropods have a head, thorax, and abdomen.

Head ------>



Thorax -------->





Abdomen --------->









  • Most arthropods have 3 main parts to their bodies: a head, a thorax, and an abdomen.
  • There are some arthropods which only have two main body parts: the cephalothorax (head and thorax fused together) and an abdomen.


Crabs are an example of an arthropod with a cephalothorax rather than a distinct head and thorax.

Crabs have a cephalothorax instead of a head and thorax.
Crabs have a cephalothorax instead of a head and thorax. | Source
malphighian tubules
malphighian tubules | Source

More characteristics of Arthropods - Open circulatory system, coelom, wings, excretory system

  • Arthropods have an open circulatory system. That means that the fluid flows out of the circulatory vessels and onto the body tissues before being collected back into the circulatory vessels again.


  • Arthropods have a coelom. A coelom is a fluid filled body cavity that contains the internal organs.


  • Many, but not all, arthropods have wings.


  • Arthropods that live on land use malphighian tubules in their excretory systems. The excretory system not only removes wastes from their bodies, it also helps them conserve water.

How it works: The malphighian tubules have blood flowing over them. Water and small particles in the water (from the blood) enter the tubules and then move to the animal's gut. As the fluid and particles moves through the gut, the water and other valuable components of the fluid are reabsorbed into the body tissues, while the waste remains in the gut and later leaves the body through the rectum.


Crab
Crab | Source

Crabs Are Arthropods

Crabs are arthropods because they have:

  • an exoskeleton
  • paired, jointed appendages
  • a segmented body
  • an open circulatory system
  • and bilateral symmetry (The right side of his body looks the same as the left - well, except for the one claw!)

© 2012 JanieceTobey

Comments? Questions? - Did you learn anything interesting about arthropods?

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    • profile image

      greatgifts4u 

      5 years ago

      Great info about some really scary looking arthropods! Scary to me anyway!

    • EpochCatcher profile image

      EpochCatcher 

      5 years ago

      Well done.

    • profile image

      anonymous 

      5 years ago

      this is really amazing fact about arthropods

    • profile image

      squidpjenkins 

      6 years ago

      very well presented, excellent work!!

    • JohnMichael2 profile image

      JohnMichael2 

      6 years ago

      wow! what a great presentation of info!

    • profile image

      Planit_Origasmi 

      6 years ago

      Creepy but cool lens. Thanks for the info!

    • MartieG profile image

      MartieG aka 'survivoryea' 

      6 years ago from Jersey Shore

      Here to visit a lens that's scarey-this one fits the bill! Very informative :>)

    • Scarlettohairy profile image

      Peggy Hazelwood 

      6 years ago from Desert Southwest, U.S.A.

      Yuck. This really creeped me out. Ooooohhh!

    • profile image

      Annamadagan 

      6 years ago

      Wow! Great pictures. I am blessing this lens for the quest to bless a lens about something you are afraid of... this definitely qualifies!

    • ajgodinho profile image

      Anthony Godinho 

      6 years ago from Ontario, Canada

      Enjoyed this lens on anthropods. It takes me back to my school days. Watching that Cicada molting was cool. Well done...blessed! :)

    • ChinaGal profile image

      ChinaGal 

      6 years ago

      Interesting lens. My son likes watching the crawdads in his grandparents' pond and my husband had a pet scorpion when he was a kid.

    • profile image

      anonymous 

      6 years ago

      Oh and fyi ... *blessed*

    • profile image

      anonymous 

      6 years ago

      Article gave me the shivers a few times but I still wanted to see it. As a great lensmaster, I was sure you'd put a good spin on this and I was right!

    • profile image

      janettemj 

      6 years ago

      my goodness! the molting Cicada took me by surprise. Cool lens.

    • profile image

      SandyPeaks 

      6 years ago

      Another informative and fascinating lens! Blessed by a SquidAngel.

    • Mauhro profile image

      Mauhro 

      6 years ago

      Lot of info here. Thanks for sharing. Very good lens.

    • profile image

      anonymous 

      6 years ago

      Brilliant presentation and a great resource!

    • Joan Haines profile image

      Joan Haines 

      6 years ago

      Love this! "Squid Angel blessed."

    • profile image

      Andy-Po 

      6 years ago

      Great lens. Very interesting.

    • profile image

      anonymous 

      6 years ago

      This lens is a great resource for parents and teachers. The Cicada molting is so cool! This is the first "Homeschool Club" lens that I've seen. I didn't know the Homeschool Club existed and am glad to see it!

    • traveller27 profile image

      traveller27 

      6 years ago

      Love all the pics.

    • squidoopets profile image

      Darcie French 

      6 years ago from Abbotsford, BC

      Brilliant - also love the arthropods photos - the molting one especially

    • profile image

      Terrie_Schultz 

      6 years ago

      Fascinating!

    • patinkc profile image

      patinkc 

      6 years ago from Midwest

      Amazing photos.

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