Meeting Abstract
Cyprids, the final larval stage of barnacles before settlement, are drag-based swimmers with six pairs of powerful thoracic appendages that beat sequentially through metachronal strokes. Like the swimming limbs of other crustaceans, cyprid limbs carry arrays of plumose setae – bristles with even smaller, short fibers (setules) distributed along two sides of each bristle. Setal arrays spread apart during power strokes (increasing the surface area and drag force of the appendage) and collapse together during recovery strokes (decreasing overall surface area and limiting drag). Cyprid thoracic appendages are unique among crustaceans in that the setules of adjacent setae are joined at their tips, forming a webbed array between setae. Three types of cross-linkage occur within and between biramous appendages: 1) within the setal fan of each podite, setules from adjacent setae connect at their tips and are also linked by a continuous thread running up the midline between adjacent setae; 2) between setal fans of podites the setules are joined at their tips; 3) between left and right appendages about eight thicker setules link medial setae of the endopodites. These cross-linkages occur in both thoracican and rhizocephalan clades. While most crustacean setae develop separately from individual sacs within the appendages of molting organisms, cyprid setae complete development beneath the cuticle of the nauplius, allowing the setular exoskeleton to fuse during development. The permanent webbing formed between setae is beneficial to drag-based swimming. Fused setules on appendages support a semi-rigid and highly ordered meshwork; this allows setal arrays to spread to a large surface area with low leakiness and promotes high thrust during power strokes of the paddle-like appendages.
