Prehensile and non-prehensile tails among syngnathid fishes: what’s the difference?

Abstract

All syngnathid fishes are characterized by a tail with a vertebral column that is surrounded by dermal Plates - four per vertebra. Seahorses and pipehorses have prehensile tails, a unique characteristic among teleosts that allows them to grasp and hold onto substrates. Pipefishes, in contrast, possess a more rigid tail. Previous research (Neutens et al., 2014) showed a wide range of variation within the skeletal morphology of different members in the syngnathid family. The goal of this study is to explore whether the diversity in the three-dimensional (3D) shape of different tail types reflects grasping performance, and to what degree grasping tails occupy a different and more constrained diversity. For this, a 3D morphometrical analysis based on surfaces was performed. Four different analyses were performed on the tail skeleton of nine species exhibiting different levels of tail grasping capacities (four pipehorse, three seahorse, one pipefish and one seadragon species) to examine the intra-individual variation across the anteroposterior and dorso-ventral axis. In the two interspecific analyses, all vertebrae and all dermal plates were mutually compared. Overall, intra-individual variation was larger in species with a prehensile tail. The analysis on the vertebrae showed differences in the length and orientation of the hemal spine as well as the inclination angle between the anterior and posterior surface of the vertebral body. This was observed at an intra-individual level across the anteroposterior axis in prehensile species and at an inter-individual level between prehensile and non-prehensile species. Across the anteroposterior axis in prehensile tails, the overall shape of the plates changes from rectangular at the anterior end to square at the posterior end. Across the dorso-ventral axis, the ventral dermal plates carry a significantly longer caudal spine than the dorsal ones in all prehensile-tailed species. It can therefore be concluded that prehensile tails exhibit a larger anteroposterior and dorso-ventral shape variation than non-prehensile ones. However, the hypothesis that there is a more constrained shape variation among prehensile species compared to non-prehensile ones had to be rejected.

Successful Use of Geochemical Tools to Trace the Geographic Origin of Long-Snouted Seahorse Hippocampus guttulatus Raised in Captivity

“…Previous studies addressing seahorse bony structure have mainly focused on its development and ossification processes [ 23 ], the morphological variation in seahorse vertebral system [ 24 , 25 ], and deformation mechanisms of its bony armor [ 4 , 26 ]. The use of the geochemical composition of seahorse bony structures to trace their geographic origin has never been previously explored.…”

Increased energy expenditure is an indirect effect of habitat structural complexity loss

“…This result is explained by the strategy of N . ophidion to resist hydrodynamics, which lacks caudal, anal and pectoral fins and instead relies on the use of a prehensile tail to hold the leaves (Neutens et al., 2017). On sand substrates, without the ability to hold on to vegetation, currents of above 12 cm/s will drag them and likely threaten their survival.…”

Swimming and defence: competing needs across ontogeny in armoured fishes (Agonidae)

“…They are cottoid fishes, related to sculpins, greenlings and other formerly 'scorpaeniform' fishes, but differ from their relatives in that all agonids have imbricating bony armoured plates similar to seahorses and sticklebacks, but with more complete body coverage reminiscent of pipefishes and pipehorses ( [11,25,26]; figure 1). However, unlike armoured pipefishes or seahorses, poachers lack the extreme exoskeletal dexterity that seahorses use to grasp substrates [19,28]. Like many other cottoids, poachers inhabit cooler marine intertidal and subtidal habitats, living on littoral slopes according to substrate preferences [29][30][31][32][33][34][35].…”