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Magnetic resonance imaging (MRI) has failed to distinguish between smaller gut regions and larger haemal sinuses in sea urchins (Echinodermata: Echinoidea).
Holland ND
,
Ghiselin MT
.
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A response to Ziegler A, Faber C, Mueller S, Bartolomaeus T: Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging. BMC Biol 2008, 6: 33.
Figure 1. Siphonal grooves versus siphons in sea urchins. (A) Gross anatomical dissection of Diadema setosum seen from the oral side after removal of the jaw apparatus (photograph by Gregory W. Rouse). Conspicuous gut regions are the esophagus (es) and stomach (st), which makes a clockwise circuit of the body from approximately 6 o'clock to 5 o'clock. The siphonal groove (indicated by arrows) and the inner marginal sinus (indicated by arrowheads) of the haemal system accompany the stomach throughout its course. (B, C) Cross sections of the inner marginal sinus (ims), siphonal groove (sg), and part of the stomach (st) of two diadematid species: (B) Diadema setosum and (C) Diadema antillarum. (D) Cross section of the inner marginal sinus (ims), siphon (si), and part of the stomach (st) of a non-diadematid sea urchin, Arbacia incisa. In all the cross sections, the inner marginal sinus contains a clot of haemal fluid.
Figure 2. Magnetic resonance imaging: potential and limitations for comparative morphological analyses. Vertical MRI sections of two sea urchin (Echinoidea) species passing from pharynx to periproct. A Psammechinus miliaris (Müller, 1771), (44 μm)3 dataset resolution, contrast agent: Magnevist. B Inset from A showing the stomach (st) with adjacent siphon (si) and inner marginal sinus (ims). C Diadema savignyi Michelin, 1845, (40 μm)3 dataset resolution, contrast agent: Magnevist. D Inset from C showing the stomach (st) with siphonal groove (sg) and adjacent inner marginal sinus (ims). Although both scans permit to differentiate various minute and large structures, the inner marginal sinus (ims) present in D. savignyi can be mistaken for a siphon. Vertical sections and magnifications were generated using the Volume Viewer in ImageJ 1.41o.
Holland,
A comparative study of gut mucous cells in thirty-seven species of the class Echinoidea (Echinodermata).
1970, Pubmed,
Echinobase
Holland,
A comparative study of gut mucous cells in thirty-seven species of the class Echinoidea (Echinodermata).
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Pubmed
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Echinobase
Smith,
Testing the molecular clock: molecular and paleontological estimates of divergence times in the Echinoidea (Echinodermata).
2006,
Pubmed
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Echinobase
Ziegler,
Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging.
2008,
Pubmed
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Echinobase
Ziegler,
Comparative morphology of the axial complex and interdependence of internal organ systems in sea urchins (Echinodermata: Echinoidea).
2009,
Pubmed
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Echinobase
