Revision of the muscular anatomy of the paired fins of the living coelacanth Latimeria chalumnae (Sarcopterygii: Actinistia)

Abstract

As a sarcopterygian fish, the extant coelacanth Latimeria has muscular paired fins, different in their skeletal and muscular anatomy from the paired fins of actinopterygians. Although the muscular anatomy of the pectoral and pelvic fins of Latimeria has been described by several studies, a detailed functional description of the muscles and their architecture has never been performed. Our detailed functional description of the muscles of the paired fins shows a more complex organization than previously described. The pectoral and pelvic fins have a different organization of their muscular anatomy, and the pelvic fin shows a more plesiomorphic configuration of the muscles since most of them are poly-articular and run from the pelvic girdle to the fin rays, an organization typical of actinopterygians. We found that the pectoral fins are stronger than the pelvic fins which is likely to be associated with the greater contribution of the pectoral fins to locomotion and manoeuvring. Finally, the study of the joint mobility of the paired fins showed that the pectoral fins show greater mobility than the pelvic fins. The reduced mobility of the pelvic fin is possibly a consequence of the morphology of the mesomeres and the large pre-axial radials.

The Evolution of Appendicular Muscles During the Fin-to-Limb Transition: Possible Insights Through Studies of Soft Tissues, a Perspective

“…Unfortunately, there was no study that compared the muscle architecture of the pectoral and pelvic fins in the same species; therefore, data were compiled across different studies. The data on the muscle architecture of the pectoral and pelvic fins of the extant coelacanth Latimeria chalumnae, as a model of a sarcopterygian fish, were taken from Huby et al (2021). We used here data on Latimeria because it is the only sarcopterygian fish with data on the muscular architecture of its appendages, even if it is not the closest living relative to Tetrapoda.…”

“…We included the data on the alligator Alligator mississippiensis (Allen et al, 2010), varanid lizards (Dick and Clemente, 2016;Cieri et al, 2020), and several mammals (Payne et al, 2005a;Ercoli et al, 2013Ercoli et al, , 2015Moore et al, 2013;Rupert et al, 2015;Warburton et al, 2015;Olson et al, 2016;Martin et al, 2019). The publications on the coelacanth (Huby et al, 2021), the alligator (Allen et al, 2010), the varanids (Dick and Clemente, 2016;Cieri et al, 2020), the short-nosed bandicoot Isoodon (Warburton et al, 2015;Martin et al, 2019) and the grison Galictis (Ercoli et al, 2013(Ercoli et al, , 2015 include both the pectoral and pelvic appendages. The data for the American badger, Taxidea taxus (Moore et al, 2013), the nine-banded armadillo, Dasypus novemcinctus (Olson et al, 2016), and the marmot Marmota monax (Rupert et al, 2015) pertain only to the forelimb, whereas the data for the horse Equus caballus (Payne et al, 2005a) pertain only to the hind limb.…”

“…This stronger fin is associated with a larger muscle volume and mass. The larger and stronger fins or limbs FIGURE 1 | Hypotheses of homology of the muscles of the pectoral (A-F) and pelvic (G-L) appendages in fish (A,D,G,J), the coelacanth, Latimeria (B,E,H,K), and the alligator (C,F,I,L); modified from Thorsen and Westneat (2005), Allen et al (2010), andHuby et al (2021). Blue, adductor profundus group; green, adductor superficialis group; orange, abductor superficialis group; red, abductor profundus group.…”