Abstract
As a basis for understanding the function of the halfbeak of the piper, Hyporhamphus ihi (Phillips), details of the structure and dimensions of the anterior lateral line on the head and lower jaw of the piper are described. The anterior lateral line is composed of a series of cranial canals; the supraorbital-postorbital canal; the suborbital canal; and the preopercular-mandibular canal which extends along the lower jaw. Each canal opens to the surface by a series of pores, and individual neuromasts exists in specialized regions of the canals between each of the pores. Piper are nocturnal planktivores and they possess the feeding structures and digestive tract suited to this diet. The hypothesis is proposed that they use the anterior lateral line system in prey detection, and the piper''s elongate body form, swimming behavior, and lack of a specialized visual system are all consistent with this hypothesis.