Invertebrates II
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   1. Arthropods

   They are invertebrates that have an exoskeleton made of chitin. When they grow, this shell remains small and it comes off it, forming another larger exoskeleton. This process is called "Ecdysis".

   The word arthropod means they have articulated legs.

   Arthropods are numerous and represent 85 % of all invertebrates.

   We can distinguish four classes:

   - Insects such as beetles, flies and lobster

   - Crustacean, such as crab , lobster and barnacle .

   - Myriapoda, such as centipedes and millipedes .

   - Arachnids, such as the spider, the scorpion and the tick.

   2. Indicate if these arthropods are: insects, crustacean, arachnid or myriapoda:

The Scorpion


The millipede


The grasshopper


The crab


La mosca


The centipede


The spider


The crab


    3. Characteristics of arthropods

  - The body has four parts: Head, thorax, abdomen and extremities. Spiders have fused head and thorax. Centipedes have the body divided into numerous segments.

   - The number of extremities is varied: insects have six legs, arachnids have eight and crustaceans and myriapoda have a variable number.

   - Eyes and antennae are In the head.

   - Arthropods breathe by the trachea and aquatic crustaceans by gills.

   - Blood circulation is open. The heart is in the dorsal part and the blood vessel pours the blood in the animal body.

   - The nervous system consists of a brain and a nerve cord that runs the body through the stomach.

   - They reproduce by eggs.

   4. Answer if these sentences are true or false:

Arthropods reproduce by eggs


The body of the centipede has four parts


Insects have six legs


Spiders have eight legs


Crustaceans have six legs


All crustaceans breathe by gills


The antennas are in the head


    5. Insects

    The insects are terrestrial arthropods with six legs. The most of them are flying. For example: the scarab (500,000 species), Butterfly (160 000 species), fly (75 000 species , with a pair of membranous wings) , grasshopper , cricket and lobster.

   6. Choose one of these words: scarab, butterfly, bee and fly

It has a pair of wings


It has four wings


There are 500 000 species


It has a poisonous sting


    7. Crustaceans

    Crustaceans are aquatic arthropods, both marine and freshwater. The number of legs varies according to the different groups. For example: lobster, crab, barnacle, prawn and crawfish.

   8. Indicate if these animals are crustaceans or insects:

The crab


The scarab


The lobster


The bee


    9. Arachnids

    They are terrestrial arthropods with eight legs. They have a fused head and thorax. For Examples: scorpion, spider and tick .

   10. Indicate if these animals are arachnids , crustaceans or insects:

The cricket


The scorpion


The barnacle


The spider


The butterfly


The crawfish


The tick


    11. The myriapoda

    Its body is divided into many segments and many legs.

   For example: the centipede and the millipede.

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®Arturo Ramo García.-Record of intellectual property of Teruel (Spain) No 141, of 29-IX-1999
Plaza Playa de Aro, 3, 1º DO 44002-TERUEL