ULTRASTRUCTURAL INVESTIGATIONS OF THE SENSORY RECEPTORS OF MACROSTOMUM CF BULBOSTYLUM (PLATHELMINTHES, MACROSTOMIDA)

The sensogram, the spectrum of sensory structures, was investigated fo r the macrostomid plathelminth Macrostomum cf. bulbostylum using light and transmission electron microscopy. Nine types of receptors could b e distinguished using morphological criteria including a rhabdomeric p hotoreceptor (with a lens structure) and two types of collar receptors . Our findings are compared with the few other investigations on (more or less) complete sensograms of free-living and parasitic plathelmint hs showing that the free-living Plathelminthes and each life cycle sta ge of most Neodermata exhibit about the same number of receptor types. The parasitic taxa, however, show a greater heterogeneity when the re ceptors of all life cycle stages of a species are considered.