The missing anatomy of the living coelacanth, Latimeria chalumnae (Smith, 1939)

Anatomical features that have not been previously described in Latimeria were sought in histological section series, tissue-stained microCT scans, MRI scans, and synchrotron scan series. The spiracular organ, ultimobranchial endocrine gland, and m. cucullaris were identified in the expected locations. In addition, a muscle arising on the medial side of the pectoral girdle is identified and compared with a muscle in a similar location that attaches to the cranial rib in lungfish; these are proposed as homologues of the tetrapod m. omohyoideus. These findings are placed in evolutionary context by comparison with selected other groups of fish, lungfish and tetrapods. The position of Latimeria as a key taxon in the fish-to-tetrapod transition is emphasised by these findings, and the findings have potential to inform research on cranial structure in extinct taxa.