HALLER ORGAN IN THE TICK FAMILY ARGASIDAE (ACARI, PARASITIFORMES, IXODIDA)

The structure of Haller's organ in all major groups of soft ticks, fam ily Argasidae, is reexamined, and hypotheses of setal homology are pro posed based on a comparative study of developmental patterns. The larv ae of most taxa have 7 setae in the anterior pit (1 serrate, 1 conical , 2 fine, 2 porose, 1 grooved) and 4 porose setae in the capsule. The postlarval stages add up to 3 setae to the anterior pit (1 serrate, 1 porose, 1 grooved) and up to 3 porose setae to the capsule. Preliminar y hypotheses of polarity, distinguishing ancestral from derived charac ter states, are generated for most characters examined by comparisons with results obtained for the other major family of ticks, Ixodidae, a nd (where possible) other members of Parasitiformes. Most of the varia bility in the setal complement of the anterior pit and capsule results from paedomorphosis, and nearly all the observed changes in the setal complement (both modifications of addition patterns and changes in fu ndamental numbers) are restricted to single species or small species g roups. A correlation between changes in Haller's organ structure and c hanges in life history patterns is suggested but cannot be confirmed b ased on presently available data.