Conjoined Parasitic Twins (Cephalo‐Thoracopagus Parasiticus) in a Free Ranging Northern Bat ( <scp> <i>Eptesicus nilssonii</i> </scp> ): A Micro‐ <scp>CT</scp> Anatomic and Genetic Survey

The detailed anatomical situation of male stillborn cephalo-thoracopagus twins in a wild ranging northern bat (Eptesicus nilssonii) is described by means of full body micro-CT scans in high resolution with three-dimensional computational reconstruction. The external anatomy was characterised by supernumerary wings and legs and marked cranial disfiguration. The most striking features of the internal anatomy were the presence of two hearts with different characteristics, three lungs with two tracheas, three kidneys as well as a doubled liver. Vascular aberrations and other organ deformities are described in detail. The monozygotic origin of the present parasitic conjoined twin was shown by genetic sequencing, analysis and relatedness calculations based on individual tissue samples from the autosite and the parasite. As the free ranging 1 year old mother of this twin returned every year to the same well monitored nursery colony in Norway to give birth to its pups, we can present the life history of the mother bat including the reproductive data of five more consecutive years. This enabled us also to evaluate the birthing process of the conjoined twin in the light of physiological behavioural birthing data.