Comparative morphology and osteology of pelvic fin-derived midline suckers in lumpfishes, snailfishes and gobies

Abstract

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species-specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.