The muscular anatomy of the pelvic fin of the extant coelacanth Latimeria chalumnae
Résumé
Cœlacanths are sarcopterygian fishes firstly known only on the fossil record and assumed extinct since the Upper Cretaceous (70My ago). The discovery of a living coelacanth, Latimeria chalumnae, offshore South Africa in 1938 was a surprise for the scientific community, but also an opportunity to study the anatomy of this close relative to tetrapods. Its discovery was followed by publications on its anatomy and the phylogeny of the group. Its paired fins are of special interest by their mono-basal articulation and their proximal endoskeleton, homologous to those of the tetrapod limbs. A recent study on the functional musculature of the pectoral fin shows that it is more complex than previously thought. We are now focusing on the pelvic fin, assuming that it also has a more complex musculature than previously described (Millot & Anthony, 1958). To answer this question, detailed dissection and anatomical description of the pelvic fins have been undertaken on an adult specimen of L. chalumnae preserved in the MNHN collections, Paris.
According to Millot & Anthony (1958), the pelvic fin musculature presents a three-layer organization: the adductor and abductor muscles form the superficial and middle layers, whereas the pronator and supinator form the deep layer. Among others, our preliminary results show that the muscle bundles of the superficial and middle layers lead to adduction or abduction movements, but also to the protraction or retraction of the fin. This complex organization of the muscle bundles is congruent with a high mobility of the pelvic fin.