Functional morphology of the nasal region of a hammerhead shark

Abstract

We describe several novel morphological features in the nasal region of the hammerhead shark Sphyrna tudes. Unlike the open, rounded incurrent nostril of non-hammerhead shark species, the incurrent nostril of S. tudes is a thin keyhole-like aperture. We discovered a groove running anterior and parallel to the incurrent nostril. This groove, dubbed the minor nasal groove to distinguish it from the larger, previously described, (major) nasal groove, is common to all eight hammerhead species. Using life-sized plastic models generated at 200 microm resolution from an X-ray scan, we also investigated flow in the nasal region. Even modest oncoming flow speeds stimulate extensive, but not complete, circulation within the model olfactory chamber, with flow passing through the two main olfactory channels. Flow crossed from one channel to another via a gap in the olfactory array, sometimes guided by the interlamellar channels. Major and minor nasal grooves, as well as directing flow into the olfactory chamber, can, in conjunction with the nasal bridge separating incurrent and excurrent nostrils, limit flow passing into the olfactory chamber, possibly to protect the delicate nasal structures. This is the first simulation of internal flow within the olfactory chamber of a shark.

A new species of Dermopristis Kearn, Whittington & Evans-Gowing, 2010 (Monogenea: Microbothriidae), with observations on associations between the gut diverticula and reproductive system and on the presence of denticles in the nasal fossae of the host Glaucostegus typus (Bennett) (Elasmobranchii: Rhinobatidae)

“…According to Abel et al (2010), nasal fossae of elasmobranchs with an active life-style are almost completely filled with wing-shaped folds or lamellae arranged in two rows side by side. Each fossa of G. typus contains similar lamellae (Fig.…”

A Computational Study of the Hydrodynamics in the Nasal Region of a Hammerhead Shark (Sphyrna tudes): Implications for Olfaction

“…Such studies [1]–[3] have provided insight into how different anatomical structures may contribute to olfaction. Externally, one of the most distinguishable features of the Sphyrnidae family is the broad, flat head known as a cephalofoil.…”

“…This unique head morphology provides a wide lateral separation between olfactory organs that may be used by the shark to resolve spatial gradients in odorant concentration, resulting in enhanced bilateral sampling for olfactory tropotaxis [2], [4], [5]. Additionally, the cephalofoil of the hammerhead shark contains a narrow groove, termed the prenarial groove (or major nasal groove [3]), that extends medially from the incurrent nostril and is thought to direct flow towards the inlet naris, thereby permitting the shark to sample a larger volume of fluid [2], [3]. Abel et al [3] also described the presence of a minor nasal groove, located anterior and parallel to the incurrent nostril, that may also direct flow toward the inlet naris while regulating the amount of flow entering the olfactory chamber, thereby protecting the fragile olfactory lamellae.…”

Molecular Dynamics Simulations of Water/Mucus Partition Coefficients for Feeding Stimulants in Fish and the Implications for Olfaction

“…The olfactory chamber of the hammerhead shark (Figure 1 A and B) contains two rows of olfactory lamellae that provide an increased surface area for chemical sensing [20], [29]. Functionally, as the shark swims, water flows through the olfactory chamber, as described by Rygg et al [20], delivering odorant to the sensory epithelium that lines each lamella (Figure 1 C).…”