Fig 1.
Rhizostoma pulmo gastrovascular system of the manubrium.
(a) Resin endocast of the whole gastrovascular system of a specimen of 14.6 cm in diameter. (b) 3D rendering obtained by X-ray microtomographic data of the resin endocast showed in (a). Tomographic reconstruction performed with an isotropic voxel size of 62.0 μm.
Fig 2.
Volume rendering of the resin endocast obtained via X-ray μCT, showing an enlarged view of Fig 1b: Detail of the stomach, subumbrellar view.
The radial canals per quadrant, emerging from the stomach are visible. Arrows indicate: two perradial canals (white), one interradial canal (red), two adradial canals (yellow) and the perradial canal passage into the manubrium (green). CT reconstruction performed with an isotropic voxel size of 62.0 μm.
Fig 3.
Relationship of the perradial canals and the juvenile mouth opening.
(a) Subumbrellar view of a young medusa, manubrium excised. White arrow indicates the remnant of the original mouth. Black arrow indicates the section of one perradial canal. The edges that delimit the canals are still partially adjacent (scale bar = 1 cm). (b) Exumbrellar view of the stomach floor of another young specimen. White arrow indicates the quadrangular central remnant of the mouth. Black arrow indicates the still partially opened edges of a perradial canal (scale bar = 0.5 cm). (c) Volume rendering of the subumbrellar region of the resin endocast, obtained by X-ray μCT. Black arrow indicates a protruding perradial canal from the stomach floor. CT reconstruction performed with an isotropic voxel size of 62.0 μm. (d) Endocast of a larger specimen (35 cm diam.). The area of adherence of the perradial canal edges is noticeably increased. Dashed lines indicate the end of the adhering stripes in the proximal portion of the manubrium (scale bar = 1 cm).
Fig 4.
Morphology of the exumbrellar limit of the stomach.
(a) Median sagittal section of the endocast showed in Fig 1b, evidencing the convexity of the stomach roof. White spot indicates the artefact due to the resin injection. CT reconstruction performed with an isotropic voxel size of 62.0 μm. (b) Endocast exumbrellar view. White arrows indicate two of the four perradial outlined ridges (scale bar = 1 cm). (c) Interradial section of a 29 cm adult evidencing the upper central protruding pyramid. Arrows indicate two of the perradial ridges (scale bar = 1.5 cm). (d) Subumbrellar view of the stomach roof of a specimen of 33 cm diam. showing the central protruding square pyramid and the four perradial ridges (scale bar = 1 cm).
Fig 5.
Morphology of the manubrium gastrovascular system.
(a) Manubrium section over the emergence of the scapulae, exumbrellar view. Visible the hemi-canals pattern (white arrows) branching from the central cavity, the internal one partially emerging. Black arrow indicates one of the further dichotomic branches of the oral arms duplication (scale bar = 0.5 cm). (b) Section at subscapular level, subumbrellar view (scale bar = 1 cm). Arrow indicates one of the hemi-canal structures. (c) Transverse section of an oral arm at sub scapular level. Larger square bracket indicates the total canal length, smaller one the medial adhering area (scale bar = 0.5 cm). (d) Same as in (c) (scale bar = 0.5 cm). (e) Subumbrellar 3D rendering of a specimen sub-volume obtained by X-ray μCT; white arrows indicate the dichotomization of two oral arms main canals, black arrow indicates the remnant of the juvenile central mouth opening. CT reconstruction performed with an isotropic voxel size of 62.0 μm. (f) Endocast of a specimen of 32 cm diam. showing the emergence of the scapular hemi-canal. Arrows indicate the upper (white) and lower (black) hemi-canal (scale bar = 1 cm). (g) Scapular canal system, upside down view. White arrow indicates one branching connected to the lower canal, black arrows indicate the terminal dichotomic branching maintaining the two hemi-canals pattern (scale bar = 1 cm). (h) Endocast of one oral arm, showing the two hemi-canals pattern (scale bar = 1 cm). (i) Stain injected in the oral arm evidences the hemi-canal pattern. Red squares indicate the correspondent trait as in (h). The juvenile anastomoses on the left will disappear in more developed medusae (scale bar = 1 cm).
Fig 6.
Morphology of the manubrium gastrovascular system.
(a) Proximal internal region of the manubrium, showing the projection of the juvenile central mouth (white arrow), distally branching into a series of small canals with terminal openings (red arrows). (b) Volume rendering obtained by X-ray μCT showing the hidden central canal and its branches (yellow). (c) Longitudinal section of the volume shown in (b), highlighting two lateral canals connected with two oral arms. (d) Magnification of the region showed in (c), featuring all the four transverse connections with the proximal bifurcations of the emerging eight oral arms (arrows indicate two of them). CT reconstruction performed with an isotropic voxel size of 62.0 μm.
Fig 7.
Graphical summary of the results of the quantitative analysis on the gastrovascular system.
(a) 3D rendering of the whole cast of the gastrovascular system measured via X-ray μCT. (b) Isosurface rendering showing the segmented gastrovascular system of the whole manubrium; false colors refer to the two different structures analyzed (blue = scapulae, red = oral arms). Color intensity is proportional to the local thickness values in the medial axis at that specific voxel. (c) Volume rendering of the cast; medial axes analysis, high intensity colors indicate the smaller canals. (d) Volume rendering of a single oral arm. (e) Thickness-labeled skeleton of the three-winged portions, each characterized by a specific hue (red, green, and blue). (f) Openings of the three different wings labeled with the three different colors as in (e). CT reconstruction performed with an isotropic voxel size of 62.0 μm.
Fig 8.
Morphometric analysis of the scapulae vs. the oral arms and thickness analysis of the three-winged portions in an oral arm.
(a) Frequency plots of the branch lengths. (b) Thickness of the scapulae vs. the oral arms. (c) 3D isosurface rendering of a single oral arm. (d) Frequency histogram of the LT values within the three wings.
Table 1.
Summary of the skeleton analysis [43].
Fig 9.
Functional anatomy of the gastrovascular system.
(a) Living specimen with stained stomach, with stain diffusion into the adradial canals after 1 min from the injection (scale bar = 1 cm). (b) Same specimen, lateral view, after 1 min from (a). Staining of the internal ring canal. Manubrium: the stain transits into the external hemi-canals, and the upper openings of the external oral arm wings (scale bar = 1 cm). (c) Similar to (a), but specimen injected with methylene blue stain (scale bar = 1 cm). Adradial canals stained. (d) Initial coloration of the inner ring canal and the outwards adjacent anastomosed canals mesh (scale bar = 1 cm). (e) Beginning of coloration of the per- and interradial canals inside the inner ring canal. Beginning of coloration of the distal ring canal (scale bar = 1 cm). (f) Umbrellar canal system now completely stained (scale bar = 1 cm).
Fig 10.
Functional anatomy of the gastrovascular system.
(a) Living specimen as in Fig 9a and 9b, with mucous stained filament expelled from the upper openings of the external wings of the oral arms (scale bar = 1 cm). (b) Live excised scapula with red stain released just near the cutting surface (left). Stain mainly flowed in the lower hemi-canal (arrow) (scale bar = 0.5 cm). (c) Live oral arm cut under the scapulae, stained as above. Stain concentrated in the outer hemi-canal (black arrow), whilst the inner hemi-canal is unstained (white arrow). The frillings of the inner wing are stained by the stain droplets initially released in the proximity of the upper cutting surface, then externally diffused (bottom left) (scale bar = 0.5 cm). (d-f) Photographs from a clip following the stain diffusion into the outer hemi-canal. Arrows indicate three successive moments of the stain flux (scale bar = 0.5 cm).
Fig 11.
Functional anatomy of the gastrovascular system.
(a) Living specimen as in Fig 9c–9e, with superimposed arrows that outline the flow sequence; I, from stomach to the inner ring canal through the adradial canals (white arrows); II, through the inner ring canal towards the per/interradial canals and towards the distal ring canal; III, through the distal ring canal towards the per/interradial canals (yellow arrows) and relative anastomoses; simultaneously a perradial outgoing flux flows from the inner ring canal junction towards the manubrium (red arrows) (scale bar = 1 cm). (b) Drawing showing the bidirectional flux in the manubrium. Blue arrows, incoming flux, red arrows, outgoing flux. Top left, magnification at scapular level.
Fig 12.
Square indicates the top left magnification of the Gulf of Trieste (Italy). Red triangles indicate the sampling areas. The red bordered area is part of the Grado Lagoon, where juvenile specimens were sampled.
Table 2.
List of collected samples and locations for Rhizostoma pulmo and R. luteum.