The aims of this study were (1) to compare the morphology of the buccal apparatus, the suspensorium and the opercle in four species of Carapidae ( Carapus acus , Encheliophis boraborensis , Encheliophis homei and Encheliophis gracilis ) and (2) to investigate the relationships between their cranial anatomy, their carnivorous diet, and their well known ability to enter holothurians. The complex and strong dentition and the wide hyomandibular with thickenings that seem to suit the constraints of the adductor mandibulae muscles partly inserted on the neurocranium are signs of a carnivorous diet. C. acus , E. boraborensis and E. homei have extremely strong buccal pieces and can protrude their upper jaws. However, in E. gracilis , the jaws are more slender, and the insertions of the A 1 along the entire length of the maxillary associated with the lack of mobility between the maxillary and the premaxillary prevent buccal protrusion. These differences could be related to the diet: C. acus , E. boraborensis and E. homei can feed on fishes and crustaceans, whereas E. gracilis feeds only on holothurian tissue. The cephalic morphology of the four species is not incompatible with entering the host. However, the neutralisation of the suboperculum spine by ‘cartilaginous’ tissue could be considered to be a particular adaptation to this behaviour.