Sarcoptiformes 32 1 



Pseudostigmatic organs are not present. The body is, as a rule, soft 

 skinned but usually has a dorsal plate or plates. The coxae form char- 

 acteristic plates. The tarsi usually have a stalked or sessile empodial 

 claw and caruncle, and when without claws the caruncle is bell-like. 

 The palpi are simple, usually with two free, seldom four, movable 

 segments. Sexual dimorphism is marked in some cases. Two pairs of 

 genital suckers are usually present, and the males generally have prom- 

 inent adanal suckers. 



The Acaridiae can be divided into the free-living type (Acaridae or 

 cheese mites), the parasitic type (Sarcoptes or itch mites), and the 

 feather- or hair-inhabiting type (feather mites) and by certain mor- 

 phological structures such as skin sclerotization and striations, but 

 actually there are not clear-cut morphological differences to be found 

 here as in the other suborders. 



Key to the Acaridiae 



1. Body without plates, or with single, lightly sclerotized propodo- 

 somal shield (occasionally hysterosomal shield present); legs not 

 modified for clasping hairs; as a whole, free-living mites or skin 

 parasites 2 



Body plates strongly sclerotized, usually with more than one well- 

 defined shield; or legs or maxillae modified for clasping hairs; 

 feather or hair mites 27 



2. Hysterosoma not segmented 3 



Hysterosoma divided into four sections by transverse sutures; 

 propodosoma with pair of bladder-like sensory setae; tarsi with 

 caruncles but no claws Pediculochelidae 



3. Chelicerae with opposed chelae, although sometimes minute 4 

 Fixed chela reduced, movable chela normally developed 17 



4. Caruncle with claws, sometimes very minute (Ensliniellidae and 

 Canestriniidae ^) 5 



Caruncle without claws 19 



5. Caruncle sessile and with claw 6 



Caruncle more or less pedunculate, on distal part of which is 

 claw, often minute 8 



1 After Vitzthum; Canestriniidae fits in very close to Sarcoptidae; in some cases the 

 claws seem to have disappeared; with different type of caruncles on tarsi. 



