Functional Morphology of the Sperm Whale (<I>Physeter macrocephalus</I>) Tongue, with Reference to Suction Feeding

Abstract

Abstract Gross and microscopic examination of the tongue and hyolingual apparatus of the sperm whale (Physeter macrocephalus) revealed numerous dis-tinct differences from those of other toothed whales and dolphins, largely reflecting the tongue’s atypi-cal position, relations, and size, and its primary role in suction ingestion, rather than prey prehen-sion or transport, as in many other odontocetes. Unlike other odontocetes, the sperm whale has a short, wide tongue that is uniquely situated at the rear of the open oral cavity. Since the tongue does not extend to the tooth row, which runs along the elongated median mandibular symphysis, it cannot easily reorient grasped prey items, yet it can posi-tion them to be swallowed or sucked directly into the oropharyngeal opening. The scarcity of intrin-sic lingual musculature (m. lingualis proprius), coupled with the relatively large paired extrinsic muscles inserting in the tongue—notably the m. hyoglossus, whose profuse fibers comprise much of the tongue root, and the m. genioglossus—suggests the tongue mainly undergoes positional, rather than shape, changes as it is retracted by the hyoid to generate negative intraoral pressures to capture and ingest prey items via suction. The tongue possesses numerous longitudinal folds or plicae, but almost no free tip; its slightly convex dorsum bears deep fissures and few sensory receptors in a multilayered and predominantly aglandular horny epithelium.Key Words: sperm whale, Physeter macrocepha-lus, tongue, hyoid, myology, morphology, suction feeding