The morphology of the larval stages of Arrenurus biscissus, A. pugionifer and A. bisulcicodulus is described. The three species belong to the subgenus Micruracarus and share several characters. The larvae of the three species differ in the shape of the dorsal plate, shape of the excretory pore plate, ratio between length of coxal plate median margins, and the numbers of pectinating setae on fifth palpal segment (PV). The larva of A. biscissus is very similar to the closely related A. sinuator. Larvae of A. pugionifer and A. bisulcicodulus resemble other Micruracarus species (A. bifidicodulus, A. inexploratus, A. integrator).

The morphology of the larval stages of Arrenurus nodosus, A. knauthei and A. stecki is described. Particular attention is paidto the different characters separating the three species. The larvae of the three species differ in the size and shape of the dorsalplate. Distinct differences appear between the proportions in the length of the lateral margins of the epimeres, which are similar in A. knauthei and A. stecki, but different in A. nodosus. There are differences in the shape of the excretory pore plates. InA. stecki the shape of the anal plate is slightly different owing to the truncated proleg. The structure of the pedipalps are verysimilar. The PIII1 setae are always bipectinate, the PIV1 is pectinate in A. knauthei and smooth in the other species, the PV6 isshort and thick in A. nodosus, and long and thin in the other two species. Distinct differences also occur in the feathering oflegs. The ITi8 seta is short in A. knauthei and long in the other two, the LITi10 seta is long in A. nodosus and short in the othertwo, and IIITi10 is thick and pectinate in A. nodosus, and smooth and fairly thin in the other two.

The larval morphology of 20 water mite species from Alpine springs is described, with that of Protzia distincta, Tartarothyas romanica, Sperchon mutilus, S. resupinus, S. violaceus, Bandakia concreta, Lebertia cuneifera, L. lativentris, L. sefvei, Atractides adnatus, A. panniculatus, A. macrolaminatus and A. walteri being presented for the first time. For the other 7 species (Panisus michaeli, Panisopsis curvifrons, Thyas palustris, Partnunia steinmanni, Sperchon thienemanni, Lebertia zschokkei and Hygrobates norvegicus), old descriptions exist but, in most cases are not accurate enough to be usable in taxonomy. These species have therefore been re-described. Some general observations on larval morphology and taxonomy are discussed. A short survey of the larval descriptions of West-Palaearctic water mites in general and of spring-living taxa in particular is given, together with a perspective for future research into larval morphology in this geographical area.