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.
The subumbrellar muscle is the largest muscle sheet and lines the inner walls of the bell above the nerve ring, while the velarium is a continuation of the subumbrella below the nerve ring forming the the bell opening.
Neurites of the subumbrella, velarium, and frenulum in Tripedalia appeared morphologically diverse.
In Tripedalia, each motor network possessed neurites as small as 1 [micro]m in diameter or as large as 5 [micro]m in diameter, although neurites of the latter size were less prevalent in the subumbrella and frenulum than in the velarium.
5) was significantly greater than that of the velarium (16.
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).
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.
The circular musculature of the velarium is continuous with that of the subumbrella below the level of the nerve ring, and is indistinguishable from it.