A comparison of the labrum-paragnath complex in five species of calanoid copepods

Abstract

Although some information is available on how calanoid copepods collect and handle food, there is very little information on the labrum and paragnaths, structures that are the last to receive food before trituration and ingestion. Five species were used to examine the nature of and differences between the labrum-paragnath complex, species with a variety of feeding modes ranging from detritivore to carnivore. The nature of the complex ranged from very simple inEucalanus bungii bungiiJohnson, 1938, to the heavily sclerotized labrum and paragnaths of the carnivoreParaeuchaeta elongata(Esterly, 1913) with its specialized anterior labral lobe. The labrum, which provides a semi-enclosed space for trituration by the mandible gnathobases, is hood shape while the columnar-shaped paragnaths, which hold and help move food towards the mandible gnathobases, contain setule and spicule armature elements. Not only the shape of the complex, but also its orientation are suggested to play roles in dictating dietary choices. The range of structures, from the simple complex ofEucalanus bungii bungiito the beak like complex ofHeterorhabdus tanneri(Claus, 1863), along with its claw-like gnathobase armature, provide an indication of the morphological diversity found in the labrum-paragnath complex of calanoid copepods.