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? • What are the main traits that all chelicerates share?
Kingdom Animalia Phylum Arthropoda Subphylum Chelicerata Subphylum Crustacea Lobster Crab Shrimp Crayfish Barnacles Isopods Class Merostomata Horseshoe crab Class Arachnida spiders Subphylum Uniramia Class Chilopoda centipedes Class Hexapoda insects Class Diplopoda millipedes
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 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
Excretion • 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.
Respiration • O2 and CO2 exchange in a book lung- series of folded membranes exposed to blood.
Circulation • 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/Sensory 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
Reproduction • 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
Reproduction • 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 • 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. male Female Enlarged pedipalps
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 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 a. Many are ectoparasitic- feeding on blood or tissue b. Some permanent (follicle mite) c. Some temporary (chigger)
Ticks- up to 3cm in length 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 a. Carry/cause disease 1. Rocky Mountain Spotted Fever- ticks 2. Lyme’s Disease- ticks
Control insect populations • Venom & silk may have medicinal value. • Mites eat dead skin cells on body. • Spider mites (& others) can kill plants/crops.