472 ARACHNIDA—ACARINA CHAP, 
The remaining families of the Prostigmata (Halacaridae, 
Hydrachnidae, sal Trombididae) all have “raptorial palps, and 
clawed or piercing chelicerae. 
Fam. 2. Halacaridae.— This is a small group of marine 
Mites. In their usually prominent capitulum they resemble the 
Bdellidae. In some respects they recall the Oribatidae, having 
hard integuments, and their legs being articulated near the 
margin of the body. They do not swim, but crawl upon weeds 
and zoophytes, or burrow in the mud. 
Fam. 3. Hydrachnidae.—The Hydrachnidae are the Fresh- 
water Mites. Their legs are provided with long close-set hairs, 
* and thus adapted for swimming. 
They are predaceous, and in their 
young stages are often parasitic on 
water insects. A familiar example 
is Atax bonzi, which lives within 
the shell of the fresh-water mussel. 
Fam. 4. Trombidiidae. — The 
predaceous palps of the Trombi- 
diidae are generally of the “ finger- 
and-thumb” type. The tarsi are 
two-clawed, without caruncle. This 
Fie. 247.—Ataz alticola, x 16. at Bs : . 
(eee Cancsnat) group may be divided into six sub- 
families. 
(i.) The LimnocHARINak or “ Mud-mites” connect the Hydrach- 
nidae with the typical Trombidiidae. They are usually velvety 
and of a red colour. They do not swim, 
but creep. The larva of Limnocharis 
aquaticus is parasitic on Gerris lacustris. 
Gi.) The CAECULINAE bear a strong 
general resemblance to the Harvestmen 
or Phalangidae. Caeculus is so similar 
to the Phalangid genus Trogulus that 
it was considered by Dufour to belong 
to the same order. 
(iii.) The TETRANYCHINAE or “ Spin- yg, 248.—Tetranychus gibbo- 
ning-mites” are phytophagous, and do ao 50. (After Canes- 
co ‘= rinl. 
much injury to plants, sucking the sap 
from the leaves and giving them a_ blistered appearance. 
Tetranychus telarius is the “ Red-spider” of popular nomenclature. 
