DE SCHEPPER*, N**; ADRIAENS, D; DE KEGEL, B; Ghent University, Belgium; Ghent University, Belgium; Ghent University, Belgium: Cranial morphological specializations related to burrowing: a case study of head- and tail-first burrowing Pisodonophis boro.

The order Anguilliformes forms a natural group of eel-like species. Life styles of these representatives cover the entire spectrum from non-burrowing to burrowing but wedging through small openings is assumed to be the plesiomorphic mode of life. This study focuses on burrowing anguilliform species in general with Pisodonophis boro (Ophichthidae) as a case study. Ophichthidae are known in literature to burrow tail-first. However aquarium observations of living specimens of Pisodonophis boro reveal them to burrow both head-first and tail-first. Furthermore, these specimens are predators, using rotational feeding. A detailed osteological and myological examination of the head of Pisodonophis boro reveals striking morphological convergence with Moringua edwardsi, a specialized burrowing moringuid with predacious feeding habits. In Pisodonophis boro the adductor mandibulae complex is hypertrophied and the anterior fibres of the A2 are anteriorly directed; the shape of the skull is elongated, tapering to the snout; the cranial bones are highly reinforced and their sutures show a high amount of overlap; the eyes are small; the coronoid process of the dentary is high and the quadrate and hyomandibula of the suspensorium form a strong entity, while the palatopterygoid is loosely connected; the opercular and suspensorial muscles are small. However, these features are more extreme in the head-first burrowing species Moringua edwardsi but appear to a lesser extent in the tail-first burrowing congrid species Heteroconger luteolus. The differences in morphology can be considered as specializations for this burrowing behaviour as well as to differences in feeding.