Head morphology of the duckbill eel, Hoplunnis punctata (Regan, 1915; Nettastomatidae: Anguilliformes) in relation to jaw elongation

Abstract

Hoplunnis punctata, a member of the Anguilliformes, is a long-snouted eel that lives in benthic habitats of the continental shelf of tropical waters. The purpose of this study was to examine the skull morphology of this little known nettastomatid and to understand the changes associated with jaw elongation as well as the implications of jaw elongation on the feeding apparatus. We present a detailed description of the cranial osteology and myology of H. punctata and how these characters differ from Conger conger (Congrinae: Congridae), a representative with moderate jaw length, and Heteroconger hassi (Heterocongrinae: Congridae), a representative with a short jaw. Shape comparison shows a caudal displacement of the hyomandibula, quadrate–mandibular articulation and opercle–hyomandibular joint, decrease in the depth of the neurocranium, and increase in the distance between the anterior suspensorial facet and the posterior end of the orbit in H. punctata as a result of jaw elongation. These characteristics along with its immobile, long maxillary and well-developed adductor mandibulae muscle complex suggest that food may be obtained by powerful biting. Jaw elongation potentially affects the functioning of the feeding apparatus in H. punctata by providing more space for the olfactory rosette, increasing biting speed and reducing drag during prey capture.