Download Invertebrate Zoology Lecture 2, March 31, 1999

Biology 212 Lecture 5: January 22&24, 2007
Phylum Arthropoda
I.
Phylum Arthropoda, the "jointed-foot" animals
A. Position in evolutionary scheme
1.
Protostomes. Know the specific features of protostome development!
2.
Coelomates: true coelom, but greatly reduced to space around heart (pericardial
cavity) just as in Phylum Mollusca
B. Key characteristics of Phylum Arthropoda
1.
Paired, jointed appendages
a)
How does this benefit the arthropods?
2.
Segmentation/specialization of body regions
a)
In some, have similar segments throughout body
b)
In most: segments combined into specialized body regions

Example: Insects have 3 regions: head, thorax and abdomen
3.
Exoskeleton composed of chitin
a)
Same materials also in mouthparts, wings, eye lens
b)
Exoskeleton is molted
C. Focus on molting
1.
Function: growth
2.
New exoskeleton built under old
a)
How is this possible, since new exoskeleton is larger than the old one?
3.
Risks
a)
Strategy of female crabs to reduce risk…
4.
Some arthropods continue to molt and grow throughout their lives.
D.
Basics of the major subphyla
1.
Subphylum Crustacea
a)
Members
b)
Characteristics

Crustose or “calcareous”

Many have gills

Eyes: type?

Feeding modes

Lobsters and crabs

Barnacles!
2.
Subphylum Uniramia (includes Hexapoda and Myriapoda)
a)
Members:
b)
Characteristics (obvious ones)

Antennae (how many pairs?)

Body regions (what are they?)

Eyes: type(s)?

Feeding modes (two general: what are they)
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3.
E.
Subphylum Chelicerata
a)
Members
b)
Characteristics

Antennae (how many pairs?)

Body regions (what are they?)

Eyes: type(s)?

Specialized feeding structures

Pedipalps

Chelicerae

Also, sucking stomach
Body plan
1.
Feeding/Digestive system
2.
Circulation/gas exchange
a)
Circulatory system: open or closed? What is the difference?
b)
Gas exchange varies among subphyla (know specifics for each
subphylum)
3.
Water/ion balance and ammonia excretion
a)
Crustacea
b)
Insecta and Chelicerata
4.
Nervous system
5.
Reproductive systems
a)
Internal fertilization
b)
Spermatophores
c)
Sperm storage
Study questions
1. Where, in the “traditional” evolutionary scheme, do the arthropods fit? Be sure you know
which major derived characteristics they have, and whether they are protostomes or
deuterostomes.
2. What are the three key characteristics of Phylum Arthropoda that set them apart from other
invertebrate phyla?
3. Besides the exoskeleton, name several other structures in an arthropod composed of cuticle.
4. What is molting? Why do arthropods molt?
5. What enables the new exoskeleton to become larger than the old one, even though the new
exoskeleton is produced beneath the old one?
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6. Name the three subphyla within the Phylum Arthropoda. List key representative members of
each subphylum. Also know how they differ in terms of
 Number of pairs of antennae
 Organization of segments into body regions
 Type of eye (simple, compound, or both?) HINT: One group can have both types.
 Key specialized structures that are used to define the subphylum (if any)
7. Describe the basic feeding behavior for representative members of each of the Subphyla of
Phylum Crustacea, including any specialized structures. (HINT: For the spider, be sure you
have described the function of the pedipalps, chelicerae and the stomach in obtaining and
ingesting food.)
 And you best know how a barnacle feeds!
8. What type of digestive system do arthropods possess (i.e. is it complete?)
9. What type of circulatory system do arthropods possess? What function usually related to
circulation is not important for the Uniramia?
10. Name and briefly describe the respiratory organs/systems of each of the major groups of
arthropods.
11. What is the major site of water/ion balance in crustaceans? What is the major site of
ammonia excretion in the crustaceans?
12. What are Malpighian tubules? Which subphyla have them? Where do they start and where
do they empty? What is the adaptive value of emptying into this particular location?
13. Describe the nervous system organization of an arthropod. Is the nerve cord dorsal or
ventral? Is it single or paired? Are there ganglia? How are they organized? Is there a brain?
Is the brain dorsal or ventral?
14. What is a spermatophore?
15. In insects, how is it possible for fertilization to occur at a different time than mating?
16. And of course, don’t forget to go back to Study Guide 3, questions 13-19 and add in all the
latest phyla to which you have been introduced! (There’ll be some redundancy with the
questions above, but that will help you learn the material!)
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