PHYLUM ARTHROPODA. SPIDERS AND THEIR ALLIES 



279 



bark, or among dead leaves on the ground, 

 a few are conspicuously light-colored and 

 frequent flowers. To some extent they can 

 change from yellow to white, or vice versa, 

 according to the color of the flower on 

 which they wait to seize insects with their 

 powerful front legs. Ex. Misumena vatia 

 (Fig. 164). 



13. Salticidae. Jumping spiders. These sun- 

 loving spiders are more abundant in the 

 tropics than in temperate regions. They 

 have the largest eyes, the keenest vision, 

 and are among the most beautifully 

 adorned of all spiders. They build no snares, 

 but stalk and pounce upon their prey, 

 hunting only in daylight. There is much 

 sexual dimorphism, and males perform 

 elaborate courtship dances before the 

 much duller-hued females. Ex. Salticus 

 scenicus (Fig. 164), common on fences 

 and the outside of buildings. 



Order 4. Palpigrada ( L. palpo, touch gen- 

 tly; gradior, walk), Palpigrada 

 (Fig. 161). Minute; abdomen 

 segmented; long caudal filament 

 with bristles; 1 family. Ex. 

 Koenenia wheeleri, Texas. 



Order 5. Pseudoscorpionida {Gx.pseudes, 

 false). Pseudoscorpions (Fig. 

 161). Small; flattened pedipalps 

 scorpionlike. Ex. Chelifer can- 

 croides, house scorpion. 



Order 6. Solpugida (L. solifuga, sun-flee- 

 ing). Solpugids (Fig. 161). 

 Head and thorax distinct; large 

 chelate chelicerae; respiration 

 by tracheae. Ex. Eremobates 

 pallipes, southern states west of 

 Mississippi. 



Order 7. Phalangida (Gr. phalangion, 

 long-legged spider). Harvest- 

 men or daddy longlegs (Fig. 

 161). Body short and ovoid; 

 cephalothorax unsegmented; ab- 

 domen segmented; pedipalps 

 long and leglike; legs usually 

 very long and slender. Ex. 

 Liobuniim vittatum. 



Order 8. Acarina (Gr. akares, mite). 

 Ticks and mites (Fig. 167). 

 Small; body short and thick; 



cephalothorax and abdomen 

 fused; abdomen unsegmented; 

 larva with 3 pairs of legs, adult 

 with 4 pairs; free-living or para- 

 sitic; world-wide. Some of the 

 principal families are as fol- 

 lows: 



1. Argasidae. Soft ticks. Ex, Ornithodoros mou- 

 bata: vector of relapsing fever in man. 



2. Ixodidae. Hard ticks. Ex, Boophilus annula- 

 tus: vector of Texas fever in cattle. 



3. Eriophyidae. Gall mites. Ex. Phyllocoptes 

 pyri: Pear-leaf blister mite. 



4. Dcmodecidae. Skin mites. Ex. Demodex fol- 

 liculoruTn: human face mite. 



5. Dermanyssidae. Chicken mites and others. 

 Ex. Dermanyssus gallinae: chicken mite. 



6. Sarcoptidae. Itch mites. Ex. Sarcoptes 

 scabiei: human 7-year itch mite. 



7. Trombidiidae. Harvest mites and chiggers. 

 Ex. Eutrombicula alfreddugesi: North Amer- 

 ican chigger mite or red bug. 



8. Tetrarhynchidae. Red spiders. Ex. Tetrarhy- 

 nchus telarius: red spider. 



9. Hydrachnidae. Fresh-water mites. Ex. Hy- 

 drachna geographical parasitic on aquatic 

 insects. 



Subclass 2, Pycnogonida (Gr. pyknos, 

 thick; gony, joint). Sea spiders 

 (Fig, 161 ) , Marine; body small; 

 legs very long; abdomen rudi- 

 mentary, Ex. Pycnogonum lit- 

 torale: sea spider. 



Subclass 3. Tardigrada (L. tardus, slow; 

 gradior, walk). Water bears 

 (Fig. 161). Microscopic; usu- 

 ally aquatic; body cylindrical, 

 unsegmented; 4 pairs of clawed 

 legs; respiratory, excretory, and 

 circulatory organs absent. Ex. 

 Macrobiotus hufelandi: fresh- 

 water water bear. 



Subclass 4. Pentastomida (Gr, pente, five; 

 stoma, mouth). Wormlike 

 arachnids (Fig. 161). Parasitic; 

 body long and ringed but not 

 segmented; respiratory, excre- 

 tory, and circulatory organs ab- 

 sent. Ex. Linguatula serrata: a 

 parasite of mammals. 



