Zoology 113 (2010) 148–157 Contents lists available at ScienceDirect Zoology journal homepage: www.elsevier.de/zool Head morphology of the duckbill eel, Hoplunnis punctata (Regan, 1915; Nettastomatidae: Anguilliformes) in relation to jaw elongation Soheil Eagderi a,b,* , Dominique Adriaens a a Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium b Department of Fisheries and Environmental Sciences, Faculty of Natural Resources, Tehran University, Karaj, Iran article info Article history: Received 7 July 2009 Received in revised form 4 September 2009 Accepted 13 September 2009 Keywords: Feeding apparatus Cranial myology Cranial osteology Congrinae Heterocongrinae 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 morphol- ogy 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 (Heterocon- grinae: 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. © 2010 Elsevier GmbH. All rights reserved. 1. Introduction The evolution of the feeding system in fishes has been the subject of many functional morphology studies (Lauder, 1982; Ferry-Graham and Lauder, 2001; Wilga, 2005; Westneat, 2004; Wainwright et al., 2007). Differences in feeding mode may be reflected in different morphological specializations of the head in relation to different functional demands (Wainwright and Bellwood, 2002). A morphological comparative analysis of the cephalic region in its proper phylogenetic context can then allow a better understanding of the morphological changes leading to extensive morphological specialization. This may then also allow a better understanding of the implications of the performance as changes occur. One aspect related to this is the elongation of the rostral region and jaw, which originated as the result of a con- vergent evolution among many teleost lineages (Westneat, 2004). The anguilliform fishes have adapted to diverse life styles, which * Corresponding author at: Biology Department, Evolutionary Morphology of Ver- tebrates, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium. Tel.: +32 9 264 52 33. E-mail address: soheil.eagderi@yahoo.com (S. Eagderi). may be linked to the wide range of cranial forms (Verraes, 1981). This cranial variation, with associated muscles, can be expected to largely reflect evolutionary patterns of feeding specialization in the Anguilliformes. We use an evolutionary perspective to compare the feeding apparatus of three species of the anguilliforms to bet- ter understand the changes involved in the elongation of the rostral region and jaws. The Nettastomatidae or duck bill eels are a group of long- snouted eels mainly found on the outer continental shelf and continental slope of the tropics. Little is known about their biology, except for their benthic habits. They are non-burrowing or crevice- dwelling eels, feeding on a variety of small fishes and invertebrates (Smith, 1989a). This study was conducted to understand the morphological peculiarities of the skull associated with the rostral region and jaw elongation and the resulting implications for the feeding appara- tus in the duckbill eel, Hoplunnis punctata. We provide a detailed description of the cranial osteology and myology of H. punctata (with the snout length (S) = 34–38% of the head length (HL)) and its differences with respect to representatives of two closely related anguilliform subfamilies: Conger conger (Congrinae: Congridae), with a moderate jaw length (S = 22–27% of HL); and Heterocon- ger hassi (Heterocongrinae: Congridae), with a short jaw length 0944-2006/$ – see front matter © 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.zool.2009.09.004