The skull osteology of the blind cave cyprinid Phreatichthys andruzzii Vinciguerra, 1924

The present article describes the morphology of the skull of Phreatichthys andruzzii Vinciguerra, 1924, blind cave fish from central Somalia. The main findings concern a general flattening of the skull and the loss of several bones (coronomeckelian, prefrontal, supratemporal, intercalar, supraopercle) belonging to the various regions of the head skeleton; but the more important modifications are shown by the orbital region, consisting in the complete disappearance of lachrymal, suborbital, sclerotics, and the substantial reduction of the other circumorbital bones. Usually the cranial lateral line canals run through the dermal bones; on the contrary in P. andruzzii the canals are nearly exclusively sheathed by thin bony muffs. These are sometimes fused to the underlying dermal bones, but in several regions they remain fully separated and independent, running through the adjoining soft tissues. The considerable degree of osteological regression shown by the skull appears to be related to the high level of adaptation to the cave environment attained by P. andruzzii.