What characteristics have made arthropods the most successful ...

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What characteristics have made arthropods the most successful phylum? How do these animals grow?
  Can you think of any disadvantage of growing this way? What will be an ideal response?

Question 2

What is the difference between invertebrate and vertebrate chordates? What organism has
  characteristics of both? What will be an ideal response?

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Answer to Question 1

ANS:Answer
should include:
 Arthropods are segmented, but not in the same way as annelids. They have clear
segments have a pair of appendages attached. These appendages have articulation that
was a successful evolutionary adaptation for arthropods. They are able to move and bend
at specific joints on the animal. Each joint allows a full range of motion.
 Arthropods have an exoskeleton. This is a strong, lightweight outer covering made of
chitin. An exoskeleton is form-fitting and moves with the animals.
 Arthropods developed lightweight striated muscles. This makes rapid movement
possible.
 An arthropod grows by molting. The exoskeleton is shed at regular intervals. Once it is
shed, the arthropod expands its tissues with water and grows a new shell.

Answer to Question 2

ANS:Answer
should include:
 Chordates, in general, are characterized as having a notochord, a tubular dorsal nervous
system, and gill slits at some point in their development.
 Invertebrate chordates are organisms that have lost their notochord as they developed.
 Vertebrate chordates have the unique characteristic of the stiffening backbone. They also
have internal skeletons made of calcified bone or cartilage. Skeletons gave protection to
organs, a foundation for muscles, and uninterrupted support during growth.
 Amphioxus is the transitional species from invertebrate to vertebrate. It swims by
undulating its body much like a fish while combing the water for food. Its well
developed dorsal nerve chord is similar to a vertebrate's spinal cord.