A novel endocast technique providing a 3D quantitative analysis of the gastrovascular system in Rhizostoma pulmo: An unexpected through-gut in cnidaria

Abstract

The investigation of jellyfish gastrovascular systems mainly focused on stain injections and dissections, negatively affected by thickness and opacity of the mesoglea. Therefore, descriptions are incomplete and data about tridimensional structures are scarce. In this work, morphological and functional anatomy of the gastrovascular system of Rhizostoma pulmo (Macri 1778) was investigated in detail with innovative techniques: resin endocasts and 3D X-ray computed microtomography. The gastrovascular system consists of a series of branching canals ending with numerous openings within the frilled margins of the oral arms. Canals presented a peculiar double hemi-canal structure with a medial adhesion area which separates centrifugal and centripetal flows. The inward flow involves only the “mouth” openings on the internal wing of the oral arm and relative hemi-canals, while the outward flow involves only the two outermost wings’ hemi-canals and relative “anal” openings on the external oral arm. The openings differentiation recalls the functional characteristics of a through-gut apparatus. We cannot define the gastrovascular system in Rhizostoma pulmo as a traditional through-gut, rather an example of adaptive convergence, that partially invalidates the paradigm of a single oral opening with both the uptake and excrete function.

A review of the role played by cilia in medusozoan feeding mechanics

“…Section III showed that the existing literature (Nielsen, 1987) has neglected the presence of cilia in cnidarians. However, we found evidence for the presence of a ciliated epidermis within Cnidaria (with the exception of Myxozoa; Canning & Okamura, 2004), with examples in Anthozoa (Wainwright & Koehl, 1976; Chia & Crawford, 1977; Shapiro et al ., 2014), Hydrozoa (Mackie et al ., 1989; Colin et al ., 2005), Cubozoa (Golz & Thurm, 1993), Staurozoa (Larson, 1980; Dawson & Hamner, 2009; Miranda et al ., 2016), and Scyphozoa (Smith, 1936; Southward, 1949, 1955; Chia et al ., 1984a; Heeger & Möller, 1987; Larson, 1987, 1997; Nagata et al ., 2016; Turk et al ., 2021; Avian et al ., 2022). The presence of this epidermis and its specific functions in the different taxa are little known and often neglected.…”