Parhedyle cryptophthalma (Westheide & Wawra, 1974) is a poorly known meiofaunal slug from the Mediterranean, inhabiting intertidal sands under direct wave impact. The present study is the first redescription of the acochlid P. cryptophthalma, confirming original results on general morphology, integumental spicules, and aberrant radula morphology by light and scanning electron microscopy. Our focus was on the central nervous system and sensory organs, using 3D reconstruction based on serial semi-thin sections and immunocytochemistry (staining of FMRFamide and Tyrosine Hydroxylase) in conjunction with confocal laser scanning microscopy. There is a mass of, yet undifferentiated, accessory ganglia anterior to the cerebral ganglia, typical for microhedylacean acochlidians. Apart from the common setting of ganglia (paired rhinophoral, cerebral, pedal, pleural, and buccal ganglia and three distinct ganglia on the visceral nerve cord), we found a putative osphradial ganglion for the first time in the microhedylacean clade. No osphradium, no Hancock’s organ and, in contrast to the original description, no pigmented eyes could be detected. Bundles of sensory cilia were found laterally on the head-foot complex and scattered cilia are present on the head appendages. FMRFamidergic immunoreactivity was detected in all cerebral ganglia but not in the accessory ganglia. Tyrosine Hydroxylase (TH) expression and aldehyde-induced
fluorescence was observed in cerebral ganglia such as pedal ganglia, in
labio tenctacular, rhinophoral, and pedal nerves and in single neurons in the anterior region of the foot sole. Central nervous and sensory features may greatly vary among acochlidians and other heterobranch taxa, and comprehensive comparative approaches are necessary to reveal their presence, function, homology, and evolution.