Abstract
A comparative study was done on the morphology and distribution of two forms in Rhysotritia ardua (C. L. KOCH, 1841) in Japan. Compared with the form M (claws on legs I-IV: 1-1-1-1), the form BT (claws on legs I-IV: 2-3-3-3) showed larger body size, stouter body form, darker body color, thicker body setae, sensilli with stronger barbation and lamellar setae more closely situated to rostral setae. No segregation was found in horizontal as well as vertical distribution of these two forms and it suggests that they cannot be treated as separate subspecies. An appropriate decision on the taxonomical treatment of these two forms will be done after ecological and biochemical studies.
