Meeting Abstract
Batrachoidiformes is a monophyletic group of mostly benthic, ambush-predatory fishes, and characteristic for having large pectoral fins. This order is unique for having the skeleton of the pectoral fin with five radial basals, in contrast to four found in other fishes. The homology of each radial basal, however, is uncertain. A hypothesis for the higher number of radial basals would be an additional segmentation of the embryonic pectoral radial plate during early life development. To investigate such question, a series of the early life stages of Plainfin Midshipmen, Porichthys notatus (5 to 28 mm TL), was collected during the summers of 2017 and 2018, and skeletal ontogeny was investigated by clearing-and-staining. Results obtained from early stages of P. notatus were used as a proxy to explain the variation in the order. The early stages of development (6-7 mm TL) of the petoral fin of P. notatus have two cartilaginous structures: a pectoral radial plate and the propterygium. Later development shows that the segmentation of the pectoral radial plate forms the four ventral radial basals. At 7-8 mm TL, the propterygium grows in its longitudinal axis and fuses with a group of cells that migrate from the pectoral radial plate, forming the dorsalmost “radial basal”. These findings have implications to the systematics of Batrachoidiformes. In genera Triathalassothia, Batrichthys, Riekertia, Halobatrachus, and Perulibatrachus, the dorsalmost basal radial (i.e., compound propterygium) remains cartilaginous, similar to found in other fishes (i.e., plesiomorphic state). All other species of Batrachoidiformes have an ossified compound propterygium and this shared feature might be an evidence of shared ancestry.
