The Functional Morphology of Frogfish Pectoral Fins

Frogfishes are a polyphyletic group of anglerfishes (Order Lophiiformes) known for their camouflaged skin, fast prey strikes, and their unusual modes of locomotion. Frogfish use their pectoral fins to walk, swim, and jet propulse underwater. One family of frogfishes (Family Antennariidae) was examined in this study to gain further insights into their unique pectoral girdle morphology. Frogfishes were CT scanned, both with and without tissue stains applied, for digital dissections of bone and muscle morphology. In addition, cleared and stained specimen were examined to determine the presence or absence of cartilage, and some gross dissections of preserved or freshly euthanized specimen were examined to investigate soft tissue morphology. Species included in this study accounted for 43.75% of species in the family. Stereolithography files of bone models for 13 species were landmarked in Stratovan Checkpoint and analyzed in R using the geomorph v4.0.5 package for geometric morphometric analysis. A Principal Component Analysis (PCA) was used to reduce the total number of variables and determine which variables contributed the most to variation. Values from the PCA were then used in an Analysis of Variance (ANOVA) to determine if any genera were significantly different from others within the study. Based on this study, it was determined that frogfishes within Family Antennariidae share similar bone and muscle morphology. All species examined had large L-shaped cleithrums and three elongate radials. The shape and size of the scapula and coracoid sockets varied between species, but all species had both sockets fused to the cleithrum and aligned with radials 1 and 3 respectively. While variation was present for all bone morphological areas of interest, only the medial apophysis had a significant p-value. Eleven muscles were noted for all of the species included in the muscle morphology examination, with Antennarius scaber being the exception with a 12th muscle that was previously noted in an earlier study. For the first time, the arrector ventralis muscle was noted in frogfishes. This study will enable future researchers to determine if frogfishes can be used as an effective model organism when studying the fin-to-limb transition and the evolution of walking in vertebrates.