The embryogenesis of the larval head of Simulium venustum Say (Diptera: Nematocera)

Abstract

The embryogenesis of the larval head of Simulium venustum Say is reexamined, as the known accounts of simuliid embryology do not describe the origin of the cephalic fans. It is shown that the cephalic fans are derived from the premandibular appendages, that the cephalic apotome is composed of both labral and protocephalic elements, that the egg burster marks the posterior limit of the embryonic labrum, and that the ventral median portion of the larval head capsule is submental in origin. The single prothoracic proleg arises as a single structure late in development.The embryogenesis of the simuliid cephalic fans is compared with that of similar structures in other nematocerous larvae. It is concluded that the cephalic fans of simuliid and the mouth brushes of Aedes larvae are not homologous.It is proposed that the cephalic fans be renamed premandibular fans, that the postgenal cleft be renamed the submental cleft, and that the hypostomial teeth be renamed the mental teeth.