Meeting Abstract

P1.101  Saturday, Jan. 4 15:30  Modification of the hyoid apparatus in Syngnathiformes LONGO, S.J.; University of California, Davis sjlongo@ucdavis.edu

Nearly all syngnathiform fishes (seahorses, pipefish, trumpetfish, etc.) are characterized by an elongated snout used for an unusual prey capture motion called pivot feeding: by rotating the head upwards, the mouth is quickly brought close to prey, which are then captured via the production of suction. Although all syngnathiforms are assumed to pivot feed, it has been shown that pivot feeding is further specialized for speed in seahorses and pipefish through power amplification. It is unknown whether other syngnathiform groups are capable of power amplification, in part because we do not know the mechanism in seahorses and pipefish. However, the key to power amplification has been hypothesized to lie in the conformation of the four-bar linkage mechanism coupling head elevation and hyoid depression. Morphological descriptions have noted that seahorses and pipefish have short knobby interhyals, which form a unique pivot joint with the suspensorium. By limiting the range of motion of the hyoid, this joint may play an important role in power amplification by allowing the four-bar linkage to become locked in place. To determine if other syngnathiforms possess this joint, I used clearing and staining and micro-CT scans to examine the hyoid apparatus and its association with the suspensorium across syngnathiforms (e.g., trumpetfish, razorfish, coronetfish) and key outgroup taxa (e.g., dragonets, goatfish). Reduced interhyals are characteristic of all syngnathiforms examined, while outgroups have long rod-like interhyals typical of suction feeding teleosts. Interestingly, a well-developed pivot joint between the interhyal and the suspensorium is present in razorfish, an early-branching syngnathiform lineage, but not as developed in some taxa more closely related to seahorses and pipefish.