Developmental variation of Heteraxinoides xanthophilis (Monogenea) on hosts of different sizes.

Heteraxinoides xanthophilis, a gill parasite of the spot, Leiostomus xanthurus, has an asymmetrical triangular-shaped haptor with multiple clamps situated along its edges. Clamps are usually attached consecutively to successive gill lamellae of the host. Worms accommodate during development to the gills of the particular size host. The number of clamps/mm along the haptor decreased with increased host size. Worms collected from 3 size classes of fish were significantly different in overall size at all stages of development. Clamps develop sequentially, with the younger, and eventually larger, clamps being anterior. Each successive clamp reaches an ultimate size determined by host size. The various stages (as indicated by the number of clamps present) at which the larval haptor is lost or the reproductive system develops are not affected by host size.