Classification 433 



Class PANTOPODA ( ). Marine arthropoda, 



body segmented, abdomen vestigial, with not more than seven pairs of 

 legs, mouth a beak. Ammothea Pycnogonoides. 



Class ARACHNOIDEA ( ). Arthropods with 



either tracheae, book lungs or book gills, or both, and no antennae. 

 Harvest-men, spiders, mites, ticks, scorpions. 



Class MYRIAPODA ( ). Arthropods with 



distinct head, one pair antennae, breathing through tracheae, whose 

 stigmata are placed in linear metameric arrangement, many legs. 

 Myriapods and millipeds, centipeds. 



Class MIRIENTOMATA ( ). Minute 



microscopic arthropoda (600-1600 micra), with six legs, a three-seg- 

 mented thorax (?), no antennae, post-embryonic increase of segments, 

 first pair of legs transformed into sense organ. These minute forms 

 were only recently discovered, and their affinity is uncertain. 



Class COLLEMBOLA ( ). Arthropods 



with six-segmented abdomen, no post-embryonic increase in segments, 

 one-jointed tarsi, few tracheae, these opening in one pair of stigmata at 

 the throat, abdomen generally with spring. Snow-fleas, springtails. 



Class CAMPODEOIDEA ( ). Arthropods with 



long body, abdomen ten segments, with cerci. No eyes, mouth-parts 

 withdrawn, no post-embryonic change in abdominal segments. Sprin- 

 tails. 



Class THYSANURA ( ). Arthropods with 



free mouth-parts and palpi, three caudal appendages, abdomen eleven 

 segments and covered with silvery scales, frequently with spring beneath. 

 Silver fish, fish moths. 



Class PTERYGOGENEA ( ). Insecta, 



hexopoda. Winged arthropods, with three pairs of legs, embryos with 

 twelve segments to abdomen, adults with all degrees of post-embryonic 

 reduction from twelve to six segments. Breathe through tracheae ; 

 stigmata linear and metameric in arrangements. True insects — i. e., 

 winged arthropods. 



Phylum CHORD ATA ( ). Animals having at 



some time during their life's history a notochord lying between the 

 nervous system and the alimentary tract, a hollow central nervous system 

 lying entirely on one side of the digestive canal, and pharyngeal slits 

 extending from the pharynx to the exterior. 



Subphylum CEPHALOCHORDA or ADELOCHORDA 

 ( ). Fish-like chordates with a permanent notochord 



composed of vacuolated cells, such as amphioxus. 



