Cephalic morphology of Pythonichthys macrurus (Heterenchelyidae: Anguilliformes): specializations for head-first burrowing

The Heterenchelyidae, a family of Anguil- liformes, are highly specialized fossorial eels. This study was conducted to evaluate the cranial specialization in relation to head-first burrowing behavior in the heteren- chelyid, Pythonichthys macrurus. Thereby, detailed descriptions are provided of the cranial myology and os- teology of P. macrurus and its differences with that of representatives of three families: the Moringuidae (Mor- ingua edwardsi), a head-first burrower; the Anguillidae (Anguilla anguilla), a nonburrowing representative and the Ophichthidae (Pisodonophis boro), a head and tail- first burrower. This comparison may help to get a better understanding of the cranial specialization of head-first burrowers in heterenchelyids and moringuids. We recog- nize as morphological adaptations to burrowing: reduced eye size, a caudoventral orientation of the anteromedial section of the adductor mandibulae muscle complex, the posterior position of the quadrate-mandibular joint, a solid conical skull, large insertion sites of epaxial and hypaxial muscle on the neurocranium, a widened ce- phalic lateral line canals extending into the dermal cav- ities, and a ventral position of the gill opening. J. Mor- phol. 271:1053-1065, 2010. 2010 Wiley-Liss, Inc.