Meeting Abstract

18.3  Friday, Jan. 4  Evolutionary morphology of the prehensile tail in syngnathid fishes: from pipefish to seahorse NEUTENS, C*; ADRIAENS, D; CHRISTIAENS, J; VAN LOO, D; DE KEGEL, B; BOISTEL, R; VAN HOOREBEKE, L; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium; Université de Poitiers, France; Ghent University, Belgium c.neutens@ugent.be

Seahorses and pipehorses both possess a prehensile tail, a unique character among teleost fishes, allowing them to grasp and hold onto substrates, like sea grasses. Recent phylogenetic studies suggest that the prehensile tail in syngnathid fishes evolved more than once and also suggest the existence of intermediate forms in the lineage giving rise to the seahorses. The caudal system of the seahorse is characterized by parallel myoseptal sheet spanning multiple – up to eight – vertebrae (compared to a conical organization in pipefishes), the presence of medial ventral muscles (absent in pipefishes) and by the reduction of the caudal part of the dermal plates covering the body (compared to solid bony armor in pipefishes). How this system could evolve is still unknown. In this study, we compared the tail morphology of seahorses and pipefishes with (1) the musculoskeletal system of two species belonging to the lineage giving rise to the seahorses, i.e. the bastard seahorse (Acentronura gracilissima) and the ribboned pipehorse (Haliichthys taeniophorus), expecting to find an intermediate morphology with characteristics of both seahorses and pipefishes and (2) the tail morphology of three pipehorse species that are nested within the pipefish lineages, expecting to find different convergent strategies to obtain a prehensile tail. To test these hypotheses, µCT-scanning and histological sectioning were combined with 3D-reconstructions.