ABSTRACT
Structures involved in conchostracan feeding are described for representatives of the five known families (Cyclestheriidae, Cyzicidae, Leptestheriidae, Limnadiidae, and Lynceidae). The labrum is a short thick process that contains several glands of unknown function. In most families the distal labrum is slightly bilobed. In the Lynceidae the labrum is larger, is not bilobed, and extends posteriorly more so than in other families. The general morphology of the mandible is similar for all families, but the lynceid mandible differs in details of the triturating surface and the mandible-fornix articulation. The maxillule is known for all families except the Lynceidae, where it is possibly represented by a small duct-like process. The maxillae are setose and well developed in all families; maxillary simple setae are directed posteriorly and may play a role in filtration, whereas stout serrate setae are directed orally and are probably for mechanical manipulation of food particles. The coxal endites of the thoracopods bear stout simple and stout serrate spines and setae and are directed orally. It is hypothesized, based upon morphology, that food is mechanically passed along the ventral food groove by these endites. A narrow esophagus leads from a comb-like fringe of setae surrounding the mouth to a wide tube-shaped foregut. In all families except the Cyclestheriidae, a large hepatopancreas filling much of the head region is connected by short ducts to the anterior foregut. The foregut of conchostracans is apparently unique in containing cells with cilia in addition to a microvillous border. The midgut lining is highly convoluted to aid in absorption. For the genus Lynceus the path of ingested food is inferred and diagrammed based on morphological observations.
