The swim system includes a cluster of pacemaker cells in each rhopalium; a conducting system in the nerve ring, which links the rhopalial pacemakers but also distributes excitatory impulses to the subumbrella; and a
subumbrellar motor nerve net, which synaptically activates the circular muscle that lines the bell cavity (Satterlie, 1979; Eichinger and Satterlie, 2014).
The
subumbrellar swim musculature of scyphozoan jellyfish presents an interesting problem for neuronal control due to several unique features.
Immunohistochemical staining of scyphomedusae with monoclonal antibodies against [alpha]- or [beta]-tubulin shows a
subumbrellar nerve net that has the distribution and neuronal characteristics of the motor nerve net that controls the swim musculature (Giant Fiber Nerve Net, also called the Motor Nerve Net; Horridge, 1956a, b; Schwab and Anderson, 1980; Anderson and Schwab, 1981).
Jetting medusae are characterized by having small, prolate bells (fineness ratio >0.5 (defined as bell length/bell width)) and constricted orifices leading to the
subumbrellar cavity (Daniel, 1983, 1985; Colin and Costello, 2002; Dabin i et al., 2006).
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).
Family Cyaneidae is distinguished from other semaeostome families on the basis of three characters: in cyaneids, tentacles arise from the subumbrella away from the bell margin, pendulous gonads hang below the subumbrella in complexly folded eversions of the
subumbrellar wall, and the stomach forms radiate pouches that terminate in rudimentary (i.e., poorly developed) branching canals only in the marginal lappets (Kramp, 1961: p.
1) and presents a restricted surface area in comparison to the lappets or
subumbrellar surfaces.
For each individual, replicate nematocyst densities were determined by examining two locations for each of the main prey capture surfaces (lappets,
subumbrellar surface, manubrium, and tentacles).
The hydromedusan velum includes both striated, circular muscle (
subumbrellar) and radial, smooth muscle (exumbrellar), so any deformation of the velar ring to form a nozzle can be accomplished with regional (asymmetric) contraction of the radial musculature.
Pieces of tissue from tentacles,
subumbrellar vesicles, and gastric filaments were smeared on a slide; nematocysts in these smears were examined using differential interference contrast microscopy at 100X magnification.
1): (1) bell margin tissue--a concentric ring about 1 cm in width, running around the perimeter of the bell; (2) oral arm tissue--the outpocketings of the gastrovascular cavity and overlying tissue layers that extend up into the water column; (3) the epithelial layer from the oral (
subumbrellar) and aboral (exumbrellar) regions of the bell; (4) isolated mesogleal tissue; and (5) samples of intact bell tissue along a radial transect extending from the bell margin to the manubrium (the gastrovascular cavity located at the center of the bell).
Oral arms 4, perradial, straight or curved at 90[degrees] angles typically counterclockwise (but occasionally variable), arising from base of manubrium; length short, reaching approximately to bell margin (thus only [+ or -] 1/3 bell diameter); extending laterally outward against
subumbrellar surface of bell.