Development and Evolution of the Muscles of the Pelvic Fin

Locomotor strategies in terrestrial tetrapods have evolved from the utilisation of sinusoidal contractions of axial musculature, evident in ancestral fish species, to the reliance on powerful and complex limb muscles to provide propulsive force. Within tetrapods, a hindlimb-dominant locomotor strategy predominates, and its evolution is considered critical for the evident success of the tetrapod transition onto land. Here, we determine the developmental mechanisms of pelvic fin muscle formation in living fish species at critical points within the vertebrate phylogeny and reveal a stepwise modification from a primitive to a more derived mode of pelvic fin muscle formation. A distinct process generates pelvic fin muscle in bony fishes that incorporates both primitive and derived characteristics of vertebrate appendicular muscle formation. We propose that the adoption of the fully derived mode of hindlimb muscle formation from this bimodal character state is an evolutionary innovation that was critical to the success of the tetrapod transition

Neue Untersuchungen \ufcber die embryonale Entwicklung der Salpen

Volume: 4Start Page: 90End Page: 17

Chromosomes of Thaliaceans

SUMMARYThe chromosomes of six species of thaliaceans have been examined. The haploid number 11 was determined for Pyrosoma atlanticum and Doliolum denticolatum; the haploid number 12 was found for Pegea confoederata, Salpa fusiformis, Thalia democratica; the haploid number 13 was found in Salpa maxima.Salpa fusiformis and Thalia democratica are strikingly akin with respect to both number and morphology of diakinetic chromosomes whereas the other species of Salpida all possess distinguishing peculiarities. Pegea confoederata takes a place apart among the thaliaceans by virtue of the minute dimension of its chromosomes.The karyology of thaliaceans appears to be well differenciated from that of other tunicates and, although ascidians and thaliaceans are the most akin to each other, it is not possible to establish a meaningful probable relationship between their chromosomes