The Arthropods




BIO190: The Class: Arthropods: Lesson 19

The Arthropods

Phylum Arthropoda (4 subphyla) The phylum arthropoda is the most extensive phylum in the animal kingdom, composed of more than three-fourths of all known species.

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Arachnid

Characteristics
1. "jointed foot"
2. bilat. sym.
3. segmented
  1. tagmata (fused segments)
    1. head, thorax, abdomen
    2. cephalothorax (prosoma), abdomen (opistosoma)
4. exoskeleton
  1. molted (ecdysis)
5. complete digestive system
6. open circulatory system
7. respiration
  1. cutaneous
  2. gills
  3. book gills
  4. book lungs
  5. tracheae
8. nervous system
  1. annelid plan
9. reproductive
  1. mostly dioecious
  2. some parthenogenesis
10. development
  1. fert. internal usually
  2. metamorphosis
11. annelids compared with arths. (pg. 371)
12. possible reasons arths are so abundant and diverse
  1. exoskeleton
    1. chitin
    2. calcium salts
    3. ecdysis
      1. some few
      2. some all through life
  2. locomotion
  3. modified appendages for various tasks
  4. sensory system well developed
  5. behavior patterns
  6. novel uses of resources

Taxonomy
There are four subphylums within the phylum Arthropoda.

Subphyla Trilobita (pg. 372)

The trilobites have been extinct for 200 million years, but were abundant during the Cambrian and Ordovician periods. The name refers to their trilobed body shape (fig. 19-1 A)

tri-lobed body form (fig. 19-1 A)

Subphyla Chelicerata(p. 372-379)

The chelicerate arthropods are an ancient group that includes the eurypterids (extinct), horseshoe crabs, spiders, ticks and mites. scorpions, and sea spiders.

6 pairs of appendages
1. pair of chelicerae
2. pair pedipalps
3. 4 pairs walking legs
4. exceptions horseshoe crab/ sea spiders
no mandibles
no antennae
nutrition
(most suck liquidfied prey)

Class Merostamata

eurypterids (fig. 19-1 B)
1. extinct
horseshoe crab (fig. 19-2)
1. "living fossil"
2. all marine
3. carapace
4. telson
5. book gills

Class Pycnogonida (fig. 19-3)

"sea spiders"
species vary - intertidal to great depths
unique feature among arths
1. some somites duplicated causing legs to be duplicated
2. ovigers
  1. males only

Class Arachinida (4 orders)

Arachnid
tagmata
1. cephalothorax (prosoma), abdomen (opistosoma)
cephalothorax bears (usually)
1. pair of chelicerae
2. pair pedipalps
  1. 4 pairs walking legs
3. beneficial vs harmful to humans (p. 374)
Order Araneae (figs. 19-5 --> 19-10)
1. Introduction to the Jumping Spiders
2. spiders
3. fangs on chelicerae
4. predaceous/carnivores
5. book lungs
  1. tracheae
6. Malpighian tubules (insects also)
7. 8 simple eyes
8. sensory setae
  1. receptor cells
9. spinning of silk
  1. silk glands
  2. strength
  3. spinnerets
  4. uses of silk
reproduction (p. 375)
1. Remember Charlotte's Web!
dangerous spiders(pp. 375- 376)
1. Spiders that Bite!
2. toxins
  1. hemolytic
  2. neurotoxin

Order Scorpionida

Scorpion FAQ
tagmata
small chelicerae compared with large pedipalps (pincers)
pectines
stinger
reproduction
1. mating dance
2. dioecious
  1. spermatophore
3. ovoviviparous or
4. viviparous

Order Opiliones

" harvestmen" and of course "harvestwomen" since they are dioecious
AKA "daddy longlegs' so "mamma longlegs"
scavengers

Order Acari (ticks and mites)

What is an acarologist?

Ticks
Another Ticks Page
Ixodes
fusion of cephalothorax and abdomen
mouthparts (mps) on capitulum
1. chelicera
  1. piercing/tearing/gripping food
2. pedipalps
  1. great variation depending on food utilized
reproduction
1. direct transfer of sperm or
2. spermatophore

Phylogeny/adaptive radiation (pg. 379)

Once you have completed the lesson, you should go to Assignment 19-1.

E-mail Sylvester Allred at Syl.Allred@nau.edu