Marb 435 1st Edition Lecture 18 Current Lecture Arthropoda 11 Subphylum Trilobitomorpha Very common in the fossil record from the cambrian to the permian Became extinct in the Permian triassic mass extinction Planktonic or benthic exclusively marine Typical arthropod characteristics Exoskeleton Segmentation Paired segmental appendages Compound eyes Subphylum Chelicerata No antennae Body divided into prosoma cephalothorax and opisthosoma abdomen 1st appendage chelicerae pincers Horseshoe Crabs The largest chelicerates up to 75 cm Living fossils fossil record dates back to almost 500 million years the only survivors in this class Only 4 species in 3 genera Limulus polyphemus on North American coast Morphology These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute No external segmentation in prosoma or opisthosoma Exoskeleton forms a carapace Long tail spine Book gills on ventral abdomen Reproduction External fertilization rare in arthropods Mating occurs during spring tides in spring and summer on US east coast Males and females migrate into shallow water and congregate in bays and estuaries Smaller male climbs onto female Female digs depression into sand and lays up to 30 000 large eggs Male releases sperm into the depression after they are laid Embryos develop into larvae that swim into the ocean at the next spring tide Horeshoe crabs medical research Hemolymph containslimulus amoebocyte lysate which clots in reaction to bacterial toxins Used to test for bacterial contamination in intravenous drugs vaccines and medical devices Horseshoe crabs are hand collected from shallow water or dredged from deeper water and approximately 30 of their hemolymph removed Horseshoe crabs are returned to their habitats Class Arachnida About 70 000 described species 80 of arachnid species are spiders mites and ticks Mostly terrestrial some have returned to aquatic habitats Modified eyes no compound eyes Up to 4 pairs of ocelli on the prosoma Morphology 1 pair of appendages chelicerae 2 pair of appendages palps or pedipalps 4 pairs of walking legs Scorpions Common in but not restricted to arid habitats Predators kill or paralyze prey with a posterior sting with poison glands Show green fluorescence under UV light Early Paleozoic scorpions were aquatic and had gills Spiders Approximately 40 000 species Terrestrial Predators feed mostly on insects Chelicerae with poison glands Cephalothorax and abdomen distinctly separated Spider Silk Forms the egg case Male forms a sperm web container to deposit sperm before transfer to female with pedipalp dragline that can be attached to substratum Nest web for prey capture Mites and Ticks About 40 000 described species Many parasites on humans animals and crops Terrestrial marine and freshwater Extremely abundant and diverse No tagmata or external segmentation Opiliones A k a Daddy Longlegs or Harvestmen No silk toxins or dangerous bites but can sometimes pinch Prosoma and opisthosoma fused together Inhabit humid habitats Predators or scavengers Pholcid Spiders A k a daddy longlegs or cellar spiders Superficially similar to Opiliones Produce neurotoxin No indication that it is toxic to humans Class Pycnogonida a k a Sea Spiders About 1000 species Exclusively marine Mostly small but polar species can attain up to 70 cm leg span Mostly bottom dwelling but some pelagic and some interstitial species Reproduction Gonochoric Sexual dimorphism females can be distinguished from males by their weak or absent ovigerous legs Single gonad that branches into the legs External fertilization Multiple gonopores unusual in arthropods Male fertilizes the eggs as they leave the gonopores Male gathers the eggs onto his ovigerous legs and broods them until they hatch Subphylum Mandibulata Appendages of the third head segment are modified for feeding as mandibles for chewing or grinding food Class Myriapoda Body divisions head and trunk One pair of antennae on the head Simple lateral eyes consisting of scattered ommatidia lacking the crystalline cone and usually not organized as compound eyes uniramous legs Gas Exchange Segmental tracheae Several tracheae open into an atrium The spiracles pores cannot close Order Chilopoda Centipedes About 2800 species Distributed worldwide from temperate climates to the tropics Mostly nocturnal Predators Habitats Soil and humus Leaf litter Caves Mosses Some intertidal species Order Diplopoda millipedes About 10 000 species estimated 70 000 undescribed species Have the most legs of any terrestrial animal up to 710 Cosmopolitan but especially abundant in the tropics Nocturnal Detritivores Have diplosegments i e segments that evolved from the fusion of two segments Often have sepugnatorial glands stink glands in each diplosegment Can sometimes squirt stinky fluids as a predator defense Spider Sedation The European pill millipede produces Glomerin and Homoglomerin compounds related to sedatives effective in vertebrates Compounds can sedate the spider for up to several days sometimes leading to the spider s death Secretion is slow sometimes the millipede dies before the spider falls asleep