APPENDIX 835 



CLASS 3. OLIGOCHAETA. Parapodia absent, chaetae few per segment. One 



order. Lumbricus, Tubifex, Aeolosoma. 

 CLASS 4. HIRUDINEA. Leeches. Parapodia and cheetae absent. With suckers. 



Order 1. Rhynchobdellida. No jaws, pharynx eversible, blood colorless. 



Order 2. Gnathobdellida. Three jaws, blood red. Hirudo. 



PHYLUM 12. ECHIUROIDEA. Adults not segmented, larvae with up to 15 segments. One 

 pair of ventral chaetae. One order. Bonnelia. Often considered to 

 be a class of the Annelida. 



PHYLUM 13. SIPUNCULOIDEA. Adults not segmented, larvae with up to 3 segments. No 

 chaetae, anus dorsal, head retractile. One order. Often considered 

 to be a class of the .Annelida. 



PHYLUM 14. PRIAPULOIDEA. Adults not segmented, larvae unknown. No chaetae, anus 

 posterior, head retractile. .No circulatory system. One order. Often 

 considered to be a class of the Annelida and sometimes a class of 

 the Aschelminthes. 



PHYLUM 15. ONYCOPHORA. Segmented, with a hemocoel, one pair of unjointed limbs 

 per segment. One order. Peripatus. Often considered to be a class 

 of the .\rthropoda. 



PHYLUM 16. ARTHROPODA. Segmented protostomous eucoelomates with a hemocoel and 



jointed legs, 

 t Subphylum 1. Trilobita. Antennae on second segment, biramous limbs on all succeed- 

 ing segments. One class with five orders. 

 Subphylum 2. Arachnomorpha. Chelicerae on third segment, no antennae. 



t CLASS 1. AGLASPIDA. Limbs on opisthosoma small but leglike. One order. 

 CLASS 2. XIPHOSURA. Kingcrabs. One order. Gill books on opisthosoma. 

 Limulus. 

 t CLASS 3. EURYPTERDA. Opisthosoma divided into mesosoma and metasoma. 

 .\pj)ciuiages of mesosoma gill like. One order. 

 CLASS 4. PYCNOGONIDA. Sea spiders. Body greatly reduced, opisthosoma 



rudimentary. One order. 

 CLASS 5. ARACHNIDA. Respiration by book lungs or trachea or both. Ap- 

 pendages of the fourth segment often specialized as pedipalps. 

 Subclass 1. Laticasfra. Mesosoma broadly joined to prosoma. 



Order 1. Scorpiones. Scorpions. Poison sting on telson, pedipalps 



chelate. 

 Order 2. Pseudoscorpiones. Like scorpions but very small, no sting. 

 Order 3. Opiliones. Daddy-longlegs or harvestmen. Pedipalps tactile, 



legs verv' long, opisthosoma very short. 

 Order 4. Acari. Mites and ticks. Sarcoptes, Dermacentor. 

 Additional orders of uncertain taxonomic affinities: 

 Order 5. Myzostomida. Parasites with a much simplified adult mor- 

 phology, usually considered to have evolved from the mites. 

 Order 6. Tardigrada. The water bears. Small aquatic or semiterrestrial 

 arthropods with a simplified morphology. Usually considered to 

 have evolved from the mites. 

 Subclass 2. Cauligastra. Constriction between mesosoma and prosoma. 



Order 1. Palpigradi. Minute, legs long, metasoma long and threadlike. 

 Orders 2, 3. Schizomida and Thelyphonida. Whip scorpions. Pedipalps 

 large and chelate, metasoma long and whiplike. 



