Cranial Architecture of Tube - snouted

21 The long snout of pipefishes and seahorses (Syngnathidae, Gasterosteiformes) is formed as an 22 elongation of the ethmoid region. This is in contrast to many other teleosts with elongate 23 snouts (e.g. Butterflyfishes) in which the snout is formed as an extension of the jaws. 24 Syngnathid fishes perform very fast suction feeding, accomplished by powerful neurocranial 25 elevation and hyoid retraction. Clearly, suction through a long and narrow tube and its 26 hydrodynamic implications can be expected to require certain adaptations in the cranium, 27 especially in musculoskeletal elements of the feeding apparatus. Not much is known about 28 which skeletal elements actually support the snout and what the effect of elongation is on 29 related structures. Here, we give a detailed morphological description of the cartilaginous and 30 bony feeding apparatus in both juvenile and adult Syngnathus rostellatus and Hippocampus 31 capensis. Our results are compared to previous morphological studies of a generalized teleost, 32 Gasterosteus aculeatus. We found that the ethmoid region is elongated early during 33 development, with the ethmoid plate, the hyosymplectic and the basihyal cartilage being 34 extended in the chondrocranium. In the juveniles of both species almost all bones are forming, 35 although only as a very thin layer. The elongation of the vomeral, mesethmoid, quadrate, 36 metapterygoid, symplectic and preopercular bones is already present. Probably because of the 37 long and specialized parental care which releases advanced developmental stages from the 38 brooding pouch, morphology of the feeding apparatus of juveniles is already very similar to 39 that of adults. We describe morphological features related to snout elongation that may be 40 considered adaptations for suction feeding; e.g. the peculiar shape of the interhyal bone and 41 its saddle-shaped articulation with the posterior ceratohyal bone might aid in explosive hyoid 42 retraction by reducing the risk of hyoid dislocation. 43