An in vivo Comparative Study of Intersegmental Flexibility in the Ophiuroid Arm

We present the first in vivo measurements of intersegmental rotation in the ophiuroid arm, comparing lateral bending performance in seven epifaunal species from Discovery Bay, Jamaica. The species studied include suspension-feeders, deposit-feeders, and scavengers, and also represent two major types of vertebral ossicle morphology. Animals were photographed with strobe illumination, and the angular deflections between arm segments were recorded. Despite considerable variation in vertebral morphology, ecology, and behavior, Discovery Bay ophiuroids show similar, overlapping distributions of maximal intersegmental rotations. Although interspecific differences in mean lateral flexibility can be statistically significant, absolute differences among species are small and of unknown functional significance. These quantitative data challenge long-standing assumptions about how the ophiuroid vertebral skeleton affects intersegmental flexibility, and how intersegmental flexibility per se affects an ophiuroid's ecological style or success.