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Journal. Differentiate between pleopods and periopods in a crayfish. Please turn in Crayfish Dissection Lab if you haven’t already done so. Journal. Choose one of the questions below to answer: How are hunting spiders different from web spinning spiders?

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  • Differentiate between pleopods and periopods in a crayfish.

  • Please turn in Crayfish Dissection Lab if you haven’t already done so.


  • Choose one of the questions below to answer:

  • How are hunting spiders different from web spinning spiders?

  • What are the main traits that all chelicerates share?

Kingdom Animalia

Phylum Arthropoda

Subphylum Chelicerata

Subphylum Crustacea







Class Merostomata

Horseshoe crab

Class Arachnida


Subphylum Uniramia

Class Chilopoda


Class Hexapoda


Class Diplopoda




  • General Characteristics

  • Two body regions

  • a. Cephalothorax- sensory, feeding, locomotion, eyes

  • b. Abdomen- digestion, reproduction, excretion, respiration

2. Paired Appendages

a. Chelicerae- first pair, pincer-like, feeding/fangs

b. Pedipalps- second pair, sensing, feeding, reproduction

3. No antennae

4. 8 walking legs

  • II. Class Merostomata

  • Horseshoe crabs

  • All marine

  • Diet- annelids, mollusks,

  • other inverts.

  • 3. Horseshoe shaped body

  • 4. Have compound eyes &

  • simple eyes.

  • 5. Telson- tail; used to flip over

  • 6. Book gills for respiration

7. Dioecious- male fertilizes eggs as female sheds them into a shallow hole. No brooding occurs.

Compound eye

Horseshoe crab vision

Class arachnida
Class Arachnida

EX: Spiders, mites, ticks, scorpions

Digestion feeding

  • Inject venom into prey which paralyzes & begins digesting organs of prey.

  • Partially digested food sucked into mouth via foregut (sucking stomach)

  • Food passed to

    • Intestine- enzyme secretion & absorption of food

    • Stercoral pocket- water gets reabsorbed from stored feces


  • Malpighian tubules- send waste to stercoral pocket

  • Water reabsorbed

  • Wastes excreted with digestive wastes as semisolid uric acid

    ** Water conservation is a major concern for many terrestrial animals. Most wastes excreted in solid form to prevent water loss.


  • O2 and CO2 exchange in a book lung- series of folded membranes exposed to blood.


  • Open circulation

  • Dorsal aorta pumps blood to sinuses around organs

  • Blood returns to aorta thru holes in heart called ostia

  • Blood contains hemocyanin (blue)- does not carry oxygen as well as human blood

  • Hemocyanin more important for “blood clotting” when limb lost.

Nervous sensory

  • Brain & ventral nerve cord

  • Setae- hair-like, can detect vibrations/motion

  • Chemoreceptors in exoskeleton to detect pheromones, smells in environment.

Nervous sensory1

4. 6-8 Simple eyes- sense light & movement

  • Classified into families based on eye number & position

    • Hunting spiders have larger, complex eyes

    • Web spinning spiders have smaller, simpler eyes


  • Dioecious

  • Spiders attract mates by:

    • Pheromones- chemicals given off by one to evoke a response in another.

    • Tactile Senses- males pluck strands of female web

      • Species specific “plucking”

      • Prevents male from becoming female’s next meal

    • Visual signals- “dancing”

  • Jumping Spider Dance


  • Males use enlarged pedipalp to transfer sperm to female

  • Females can deposit 3000 eggs in one silk sac!

  • Females may take care of young during & after development

  • Some spiderlings practice ballooning- let out silk line that acts as “parachute” to distribute young spiderling to new habitat- reduces competition among spiderlings.

Spider adaptations
Spider Adaptations

  • Silk gland- produces silk (protein)

  • Spinnerets- spin silk which hardens when it hits the air.

  • Silk used to make webs, egg sacs, line a nest/retreat, ballooning.

  • All spiders have silk glands, not all make webs!

  • Have oil on feet that keep them from sticking to silk.

  • All spiders are venomous, only two toxic to humans

Dangerous Spiders of United States

a. Black widow- shiny black w/red hour glass on ventral surface of abdomen.



Enlarged pedipalps

b. Brown Recluse- violin shape on cephalothorax

Myth: Daddy long legs are the most venomous spiders in the world but lack mouthparts to inject venom.

  • Truth:

  • Daddy longlegs (harvestmen) are not spiders.

  • Do not make silk & do not have venom glands.

  • Have “claw-like” fingers.

  • Produce smelly fluid when disturbed.

Scorpions world but lack mouthparts to inject venom.

a. Nocturnal

b. Venom gland & stinger in tail

c. Modified pedipalps- pincers for grasping food/defense

d. Courtship dance where male “lays” sperm case and female “sits” on case to pick up sperm

e. 20-40 young brooded by mother on her back for about 1 month

Mites- 1mm or less in size female “sits” on case to pick up sperm

a. Many are ectoparasitic- feeding on blood or tissue

b. Some permanent (follicle mite)

c. Some temporary (chigger)

Ticks- up to 3cm in length female “sits” on case to pick up sperm

a. All ectoparasites.

b. Bodies expand as they feed.

c. Breeding occurs on host.

d. Female drops off & lays eggs.

e. Can carry disease.

Economic/Environmental Significance female “sits” on case to pick up sperm

a. Carry/cause disease

1. Rocky Mountain Spotted Fever- ticks

2. Lyme’s Disease- ticks

  • Control female “sits” on case to pick up sperminsect populations

  • Venom & silk may have medicinal value.

  • Mites eat dead skin cells on body.

  • Spider mites (& others) can kill plants/crops.

Brown Recluse female “sits” on case to pick up sperm

Day 1 female “sits” on case to pick up sperm

Day 10 female “sits” on case to pick up sperm