Naupliar development of Pseudocyclops sp. (Copepoda: Calanoida: Pseudocyclopidae): description of an unusual set of character states

Abstract

Abstract Background Naupliar development is known for only one other species of the calanoid taxon Pseudocyclopidae as yet. Results Six naupliar stages are described from an as yet unnamed population of Pseudocyclops cultured at the John G. Shedd Aquarium in Chicago, IL. The naupliar body is divided into a deep anterior section and a shallow posterior section, although the posterior section is poorly defined at NI. The posterior section bears a long, thin mediodorsal seta; short thick setae are added during molts to NIII ~ NV. The posterior section does not bear limb buds except for the caudal ramus and is presumed to represent the anal segment of the copepod. Throughout naupliar development, the antennule is five-segmented, a uniquely high number for a calanoid copepod. The distal segment is broadened, and three proximal segments are foreshortened during the molt to NIII, and remain so thereafter. Setae are added dorsally and ventrally to the distal segment during each molt. The naupliar arthrite is a simple, seta-like structure on the coxa of the antenna of all naupliar stages. On the exopod of the antenna, setae are added to the segment adjacent to the proximal one during molts to NIV ~ NVI in a manner consistent with the model of ramal patterning. The gnathobase is added to the coxa of the mandible during the molt to NIV, but its ventral attenuations are lost during the molt to NVI. The endopod of the mandible significantly changes between stages NIII and NIV; setae originate dorsally rather than ventrally on the proximal endopodal segment. These unique changes are reversed during the molt to NVI. Conclusions Many of these changes have not been reported for any other calanoid. The morphological restoration at NVI is particularly noteworthy.