Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging-0

Igestive tract. Resolution: (81 μm), no contrast agent added. The two specimens show a high degree of similarity in their overall internal architecture. Arrows indicate paramagnetic gut content. (C), (D) Effects of a contrast agent on image quality. MRI sections at the height of perignathic girdle and lower stomach. Resolution: (81 μm). This freshly fixed specimen was scanned (C) before and (D) after the application of a contrast agent, Magnevist. Arrows indicate susceptibility artefacts. (E), (F) Comparison of a freshly fixed and a museum specimen. MRI sections at the height of gonads and upper oesophagus. Resolution: (81 μm). The 135-year-old museum specimen (F) gives imaging results comparable to the freshly fixed specimen (E). Both specimens were scanned with contrast agent added. Orientation: ambulacrum II facing upwards. Scale bar: 0.5 cm. ac, axial complex; al, Aristotle's lantern; am, ampulla; es, oesophagus; go, gonad; im, interpyramidal muscle; in, intestine; is, inner marginal sinus; l m, lantern muscle; os, outer marginal sinus; pg, perignathic girdle; re, rectum; si, siphon; st, stomach; to, tooth.<p><b>Copyright information:</b></p><p>Taken from "Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging"</p><p>http://www.biomedcentral.com/1741-7007/6/33</p><p>BMC Biology 2008;6():33-33.</p><p>Published online 23 Jul 2008</p><p>PMCID:PMC2500006.</p><p></p

Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging-6

Igestive tract. Resolution: (81 μm), no contrast agent added. The two specimens show a high degree of similarity in their overall internal architecture. Arrows indicate paramagnetic gut content. (C), (D) Effects of a contrast agent on image quality. MRI sections at the height of perignathic girdle and lower stomach. Resolution: (81 μm). This freshly fixed specimen was scanned (C) before and (D) after the application of a contrast agent, Magnevist. Arrows indicate susceptibility artefacts. (E), (F) Comparison of a freshly fixed and a museum specimen. MRI sections at the height of gonads and upper oesophagus. Resolution: (81 μm). The 135-year-old museum specimen (F) gives imaging results comparable to the freshly fixed specimen (E). Both specimens were scanned with contrast agent added. Orientation: ambulacrum II facing upwards. Scale bar: 0.5 cm. ac, axial complex; al, Aristotle's lantern; am, ampulla; es, oesophagus; go, gonad; im, interpyramidal muscle; in, intestine; is, inner marginal sinus; l m, lantern muscle; os, outer marginal sinus; pg, perignathic girdle; re, rectum; si, siphon; st, stomach; to, tooth.<p><b>Copyright information:</b></p><p>Taken from "Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging"</p><p>http://www.biomedcentral.com/1741-7007/6/33</p><p>BMC Biology 2008;6():33-33.</p><p>Published online 23 Jul 2008</p><p>PMCID:PMC2500006.</p><p></p

Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging-4

Grams show an aboral view, the lower diagrams a lateral view with the anterior side (ambulacrum III) oriented towards the right-hand side. Arrows indicate the position of the junction of the gastric caecum with the stomach. (A) , Echinoneoida. (B) , Cassiduloida. Species of this sea urchin taxon presumably all possess a highly reduced gastric caecum consisting of numerous small blindly ending sacs. (C) , Holasteroida. (D) , Spatangoida. Scale bar: 0.5 cm.<p><b>Copyright information:</b></p><p>Taken from "Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging"</p><p>http://www.biomedcentral.com/1741-7007/6/33</p><p>BMC Biology 2008;6():33-33.</p><p>Published online 23 Jul 2008</p><p>PMCID:PMC2500006.</p><p></p

Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging-2

Odels of reconstructed selected internal organs, stepwise turned by 90°: (C) aboral view (interambulacrum 5 facing upwards); (D) lateral view (interambulacrum 5 at back); (E) oral view (interambulacrum 5 facing downwards). The buccal sacs of as well as the siphon of could not be seen on the magnetic resonance imaging sections. Scale bar: 1 cm. The colour legend specifies organ designation.<p><b>Copyright information:</b></p><p>Taken from "Systematic comparison and reconstruction of sea urchin (Echinoidea) internal anatomy: a novel approach using magnetic resonance imaging"</p><p>http://www.biomedcentral.com/1741-7007/6/33</p><p>BMC Biology 2008;6():33-33.</p><p>Published online 23 Jul 2008</p><p>PMCID:PMC2500006.</p><p></p

Histological observations on juvenile and adult sea urchin protractor muscles.

<p>The microstructure of this muscle is largely comparable in sea urchins. Data accumulated from various sources.</p

Measurements of test, lantern, and protractor muscle dimensions in different representative sea urchin species.

<p>These values are based on 3D MRI scans of a single specimen per species and size group. The muscle parameters were measured at the mid-level of each of the ten protractor muscles and then averaged. In case of the frilled protractor muscles, the calculations of muscle area, volume, and surface area are based on the presence of five lobes on average. The surface area of the protractor muscle is that oriented towards the interradial cavity. The values for protractor muscle volume and surface area (last two lines, in bold) served as the basis for the conclusions presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037520#pone-0037520-g007" target="_blank">Fig. 7</a>.</p

The distribution of frilled protractor muscles is in support of the taxon Odontophora.

<p>(A) Phylogeny of sea urchins (Echinodermata: Echinoidea) based on results obtained by Kroh & Smith <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037520#pone.0037520-Kroh1" target="_blank">[67]</a>. The four major events of putative improvements in lantern mechanics have been mapped onto the tree. (B–G) Virtual horizontal sections through MRI datasets with 78×78×500 µm resolution of the lanterns of large adult sea urchins with about 5–8 cm test diameter. The species analyzed represent six families: (B) <i>Arbacia lixula</i> (Arbaciidae), (C) <i>Echinus esculentus</i> (Echinidae), (D) <i>Paracentrotus lividus</i> (Parechinidae), (E) <i>Sphaerechinus granularis</i> (Toxopneustidae), (F) <i>Echinometra mathaei</i> (Echinometridae), and (G) <i>Strongylocentrotus purpuratus</i> (Strongylocentrotidae). lo = lobe.</p

Distribution of frilled protractor muscles in derived “regular” sea urchins.

<p>A total of 49 echinacean (Echinoidea: Echinacea) species were analyzed by MRI, but this table also lists those genera for which no data are yet available. Representative species from all other sea urchin taxa that possess a lantern, and which have previously been analyzed by MRI (i.e., Cidaroida, Echinothurioida, “Diadematoida”, Pedinoida, Salenioida, Clypeasteroida), do not have frilled protractor muscles. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037520#pone.0037520-Ziegler6" target="_blank">[54]</a> for a full list of sea urchin species analyzed using MRI. Taxonomic arrangement of species according to Kroh & Mooi <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037520#pone.0037520-Kroh2" target="_blank">[83]</a>. n/a = not available.</p

Comparison of protractor muscle shape in selected derived “regular” sea urchin species.

<p>Frilled protractor muscles can only be found in sea urchin species of the families Toxopneustidae, Echinometridae, and Strongylocentrotidae (K–P). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037520#pone-0037520-g006" target="_blank">Fig. 6</a> for a phylogeny of the Echinoidea, while <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037520#pone-0037520-t003" target="_blank">Table 3</a> lists character distribution in all 49 echinacean species analyzed in this study. (A) <i>Stomopneustes variolaris</i> (Stomopneustidae). (B) <i>Arbacia dufresnii</i> (Arbaciidae). (C) <i>Parasalenia gratiosa</i> (Parasaleniidae). (D) <i>Temnopleurus toreumaticus</i> and (E) <i>Pseudechinus magellanicus</i> (Temnopleuridae). (F) <i>Trigonocidaris albida</i> (Trigonocidaridae). (G) <i>Polyechinus agulhensis</i> and (H) <i>Sterechinus neumayeri</i> (Echinidae). (I) <i>Parechinus angulosus</i> and (J) <i>Psammechinus microtuberculatus</i> (Parechinidae). (K) <i>Toxopneustes pileolus</i> and (L) <i>Sphaerechinus granularis</i> (Toxopneustidae). (M) <i>Echinometra lucunter</i> and (N) <i>Heterocentrotus mammilatus</i> (Echinometridae). (O) <i>Pseudocentrotus depressus</i> and (P) <i>Hemicentrotus pulcherrimus</i> (Strongylocentrotidae). (A–E), (G–K), and (N–P) based on MRI datasets with 50×50×200 µm resolution. (F) based on a MRI dataset with 32 µm isotropic voxel resolution. (L, M) based on MRI datasets with 78×78×500 µm resolution. lo = lobe.</p

Illustration of the close interrelationship between lantern protractor muscles and buccal sacs in derived “regular” sea urchins, exemplified by <i>Strongylocentrotus purpuratus</i>.

<p>(A) Photograph of the oral part of the interambulacrum showing the location of the paired buccal sacs. (B) Volume-rendered model of a μCT dataset with 27 µm isotropic voxel resolution showing the same view as in (A), but soft tissues are inapparent due to the type of analysis employed (i.e., X-ray). The dotted line indicates the location of a single buccal sac. (C) Virtual vertical section through a MRI dataset with 42 µm isotropic voxel resolution. The lumen of the buccal sacs is continuous with the interradial cavity. The labels marked (D–I) indicate the location of the horizontal sections shown hereafter. (D–I) Virtual horizontal sections through a MRI dataset with 78×78×500 µm resolution. The protractor muscles are located directly above the buccal notches. am = ambulacrum, bn = buccal notch, bp = buccal plate, bs = buccal sac, ce = compass elevator muscle, es = exterior septum, ic = interradial cavity, im = interambulacrum, in = intestine, lo = lobe, pe = peristome, pm = peristomial membrane, pr = protractor muscle, pv = perivisceral coelom, py = pyramid, sp = spine, st = stomach, tf = tube foot, to = tooth.</p