Rhopalium


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Rho`pa´li`um


n.1.(Zool.) One of the marginal sensory bodies of medusæ belonging to the Discophora.
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The RNS has a total of about 1000 neurons, excluding the photoreceptors, and forms a densely packed neuropil in the center of the rhopalium. The RNS is involved in visual processing and behavioral control, including generating the pacemaker signal, which sets the swim pulse frequency in a 1:1 manner (Satterlie, 1979, 2002: Garm and Bielecki, 2008).
Here we test the hypothesis that the Caribbean box jellyfish Tripedalia cystophora Conant, 1897 is able to regenerate an ablated rhopalium to full functionality.
rainensis, the former based mainly on medusa size, bell wart size, and an apparent reduced number of eyes per rhopalium (compared with other cubozoans).
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).
For recordings from the "pacemaker region" of a rhopalium, the electrode was placed on the aboral surface of the rhopalium (side opposite the eyes; inset in Fig.
In the lappets of the arms, away from the rhopalium, the FMRF-IR network was more random in neurite orientation relative to the strict radial orientation of tubulin-IR neurites (Fig.
FMRFamide immunoreactivity in the rhopalium was localized to a small network of cells surrounding the attachment site of the rhopalial stalk, as previously described (Martin, 2004; Skogh et ah, 2006; Parkefelt and Ekstrom, 2009).
Each rhopalium had six eyes: one lower lens eye with a maximum diameter of 230 [micro]m, one upper lens eye with a maximum diameter of 150 [micro]m, a pair of pit eyes with a diameter of 20-30 [micro]m, and a pair of slit eyes with a length of 50-70 [micro]m (Fig.
Four perradial and four interradial rhopalia in deep pits, surrounded by two thickened lips in subumbrella, [approximately equal to]27% of marginal bell radius (= 8.19 cm) from bell margin; rhopaliar pit depth [approximately equal to]1 mm, rhopaliar pit width [approximately equal to] 4.2 mm, rhopaliar pit length [approximately equal to] 6.9 mm; rhopalium has simple statocyst without obvious ocellus (Fig.
Each rhopalium contains a statolith and six eyes: two camera-type lensed eyes (with cornea, retina, and lens), and four simple eyes (two slit-shaped ocelli and two pit-shaped ocelli) (Berger, 1898; Conant, 1898).
At each of the four perradii, a rhopalium hangs in an exumbrellar concavity (niche), a short distance up from the margin.
With 8 marginal arms, each with a terminal rhopalium flanked by 2 lappets.