Umbrella of <i>Mastigias papua</i> (Scyphozoa: Rhizostomeae: Mastigiidae): hardness and cytomorphology with remarks on colors

Abstract

Mastigias papua, known as the golden (or spotted) jellyfish, is an epipelagic jellyfish widely distributed in the warm waters of the West Pacific. This jellyfish has a brownish body, owing to zooxanthellae, and white spots. We measured the maximum force to pierce the umbrella, which averaged 94-144 mm in diameter, to evaluate the hardness of M. papua, and returned a range of 0.14-0.45 N. Correlation analyses indicate that when the M. papua medusa grows (i.e., becomes heavier), the umbrella becomes larger in diameter, as well as thicker and harder within the size range we examined. However, a significant relationship between the hardness of the umbrellar apex and the thickness of the umbrella was not obtained. White spots are comprised of loose aggregates of mesogleal cells containing reflective granules. Since the white spots and the transparent parts were not significantly different in hardness, the spots were unlikely to strengthen the umbrella. The primary function of the spots may be the shading of solar radiation. Most of the zooxanthellae are located in mesogleal cells, and often beneath the exumbrellar epidermis. Therefore, light shading by white spots may be unnecessary for the zooxanthellae in mesogleal cells.

The mesoglea buffers the physico-chemical microenvironment of photosymbionts in the upside-down jellyfish Cassiopea sp.

“…Cassiopea contain distinct white striated patterns in dense layers along the rhopalia canals in the bell and under oral arms (see white patches in Figure 1B; Bigelow, 1900). While little is known about host pigments in Cassiopea and other rhizostome jellyfish (Hamaguchi et al, 2021;Lawley et al, 2021), Frontiers in Ecology and Evolution 06 frontiersin.org our reflection data (compare for example rhopalia canal with anastomosing tissue in Figure 2) suggests that the white pigmented tissue can play a role in scattering and reflection of light in Cassiopea medusae, similar to host pigments and the skeleton in reef-building corals (Wangpraseurt et al, 2014a;Jacques et al, 2019). More detailed analyses are required to understand the full potential of lightmodulating host pigments in Cassiopea, and how the holobiont might respond and grow under various light regimes.…”

The mesoglea buffers the physico-chemical microenvironment of photosymbionts in the upside-down jellyfishCassiopeasp

“…Cassiopea contain distinct white striated patterns in dense layers along the rhopalia canals in the bell and under oral arms (see white patches in Figure 1B) (Bigelow, 1900). While little is known about host pigments in Cassiopea and other rhizostome jellyfish (Hamaguchi et al, 2021;Lawley et al, 2021), our reflection data (compare e.g. rhopalia canal with anastomosing tissue in Figure 2) suggests that the white pigmented tissue can play a role in scattering and reflection of light in Cassiopea medusae, similar to host pigments and the skeleton in reef building corals (Wangpraseurt et al, 2014a;Jacques et al, 2019).…”