Jetting medusae generally possess small, prolate bells (i.e., high aspect or fineness ratio) with constricted orifices leading to their subumbrellar cavities (Colin and Costello, 2002; Dabiri et al., 2006).
In contrast, rowing medusae usually possess oblate bells (i.e., low fineness ratio) with large subumbrellar orifices.
Changes in bell morphology during development were quantified by measuring the fineness ratio, F, and velar aperture ratio, [R.sub.v], of different sized medusae when they were in a fully expanded, relaxed state (Weston et at, 2009).
Instantaneous fineness ratio, [F.sub.i], denotes the fineness ratio of medusae at a given point in the swimming cycle and is used to compare variations in changes of bell shape throughout pulsations of different medusae.
Profiles of fineness ratio ([F.sub.i]) over time of a small (0.17 cm diam.) and a large (0.5 cm diam.) medusa illustrate these kinematic differences (Fig.
