Meeting Abstract
38.3 Monday, Jan. 5 Under pressure: Ventilatory and suction feeding mechanics of ratfishes (Chimaeroidea) FERRY-GRAHAM, LA*; SUMMERS, AP; DEAN, M; GROGAN, E; Moss Landing Marine Labs lfgraham@mlml.calstate.edu
Holocephalans possess a fused upper jaw and a non-suspensory hyoid. These features, along with robust tooth plates, are thought to be associated with a durophagous foraging habit that arose coincident with the evolution of this group. However, extant holocephalans (Chimaeroidea) tend to show a trend towards reduction of the tooth plates and may rely on suction to capture prey. This implies that suction is being generated in a mechanical system where the upper jaw cannot protrude and the hyoid cannot depress, posing serious limitations on suction generation as we have come to understand it (based upon studies of elasmobranchs and actinopterygians). As a first attempt at understanding if, and how, suction is generated within chimaeroids, we measured intra-oral pressures in Hydrolagus colliei and Callorhynchus callorhynchus during ventilation and prey capture. Pressure transducers were implanted in the orobranchial and parabranchial cavities, and pressure was recorded during several modes of respiration, ranging from active pumping with paired fin movement to quiescent ventilation, and during prey capture. Comparison of the patterns of pressure fluctuations allowed us to produce a general model of flow, which has several periods of reversal, and the associated kinematics of ventilation for the two species. In contrast to the two-pump (i.e, suction-pressure) models prevalent in elasmobranchs and actinopterygians, a single pump appeared to dominate in chimaeroids. We postulate that during ventilation, water is drawn into the orobranchial cavity using a very low-pressure suction pump, on the order of 100-1000 Pa. Casts of the orobranchial cavities indicate that the chamber expands only a small fraction (~20%) due to the shape and orientation of the branchial arches. Despite this, water and prey were clearly observed being drawn into the open mouth during feeding events.
