For subumbrellar recordings, the electrodes were attached directly to the nerve ring, on the subumbrella or velarium
about 1 mm from the nerve ring (= near the nerve ring), or in the center of a muscle sheet quadrant.
This may have implications for turning behavior since asymmetric contractions of the velarium underlie nozzle formation of the bell aperture for directional swimming (Gladfelter, 1973; Petie et al., 2011).
Here we provide a quantitative confirmation of network density differences in the subumbrella, velarium, and frenula within and between cubomedusan species, as part of a thorough examination of their ectodermal nervous system.
The perradial frenula are three-dimensional muscle sheets, oriented perpendicular to the 2-dimensional subumbrella and velarium. In Carybdea, this muscle sheet was excised and spread flat for viewing.
The subumbrella, velarium, and frenulum are the three effector components of the swim system, and each muscle sheet has a unique motor network (Fig.
Neurites of the subumbrella, velarium, and frenulum in Tripedalia appeared morphologically diverse.
The velarium is analogous, but not homologous, to the velum of hydrozoan medusae.
In cubomedusae, velarial muscle fibers are all circular and striated, yet the velarium clearly forms a directional nozzle during turning (Gladfelter, 1973).
In our investigation of the neural and muscular organization of the swim system of the cubomedusa Tripedalia cystophora Conant, 1897, our attention was drawn to the four velarial frenula--buttress-like muscular brackets that brace the right-angle connection between the velarium and subumbrella in the perradii.
This velarium narrows the bell opening during a swim contraction and thus serves the same function as the velum of hydromedusae (Gladfelter, 1973).
2), lining nearly the entire subumbrellar cavity and the subumbrellar side of the velarium. This musculature provides the main motive force for ejecting water from the subumbrellar cavity during swimming and for narrowing the velarium to form a nozzle with a restricted diameter.