CHIGGERS — FARRELL 115 



Type of genus: Euschongastia americana Ewing, 1938 ( = 

 Euschdngastia sciuricola (Ewing, 1925)). Monotypic. 



Morphology 



All chiggers have the same basic external form. The size is 

 small, rarely more than a millimeter in length even when heavily 

 engorged and greatly flattened in preservation on slides. (In 

 this paper the dimensions of length and width are given in 

 microns.) Colors range through white, cream, yellow, and various 

 intensities or shades of red. The body is oval or ovoid in shape, 

 more or less inflated, in one unit without apparent segments. 

 Attached to the anteroventral portion are two pairs of jointed 

 appendages, the pedipalps and the chelicerae, which constitute 

 the mouthparts or gnathosoma. From the base of each palp a 

 flaplike process, the galea, curves forward and upward around 

 the anterolateral surface of each chelicera. Immediately posterior 

 to the gnathosoma on the lateral portions of the ventral surface 

 are three pairs of jointed walking legs terminating in two lateral 

 claws and a median empodium. On the anterodorsal surface, 

 slightly posterior to the gnathosoma, is a sclerotized plate, the 

 scutum. One or two pairs of simple eyes, usually, are located 

 lateral to the scutum. The body surface is covered with cuticular 

 striae which generally encircle the scutum and the basal segments 

 of the legs. Posteriorly the striae tend to run at right angles to 

 the longitudinal body axis. The anus is situated on the ventral 

 surface considerably anterior to the apparent posterior end of 

 the mite. The mouth is not obvious but is located at the bases 

 of the chelicerae and the palps. The body is clothed with trans- 

 verse rows of setae. These setae are usually more or less plumed 

 by setules, tapered projections from the central shaft. The galeae, 

 the segments of the palps, and the segments of the legs bear 

 setae which are nude or plumed with setules. Nude striated 

 setae may be found on the final segment of the palps and on the 

 three distal segments of the walking legs. The scutum carries 

 setae, usually with setules, which vary in number in various 

 groups of chiggers. Two specialized setae, the sensillae, are 

 always found on the scutum. The sensillae arise from pits, the 

 pseudostigmata. In some groups of chiggers true stigmata are 

 located near the base of the gnathosoma. Indented in the pos- 

 terior edge of the first or proximal segment of the first pair of 

 walking legs is a pit, the urstigmen. The scutum, segments of 

 the palps, the basal segment of the chelicerae, and the segments 



