Functional morphology of the olfactory organ of two carcharhinid shark species

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Abstract
The paired olfactory organs of both the lemon shark (Negaprion brevirostris) and the silky shark (Carcharhinus falciformis) are located in solid cartilaginous nasal capsules, which open at the ventral side of the snout and are entirely separate from the mouth. The olfactory rosette consists of two rows of lamellae arising from a central raphe. The lamellae possess secondary folds covered with sensory epithelium, which contains microvillous receptor cells, supporting cells with both cilia and microvilli, basal cells, and goblet cells. No ciliated receptor cells were found. Gaps between facing lamellae connect the inlet chamber with the outlet chamber. The inlet chamber receives the ventilatory water through the incurrent nostril and the outlet chamber discharges the water through the excurrent nostril. A nasal flap, a septum, and paired valve flaps form an incomplete barrier between incurrent and excurrent nostrils and may have hydrodynamic functions, which are discussed.