Structural design of the echinoid’s trabecular system

Abstract

The multi-plated skeleton of echinoids is made of the stereom, a light-weight construction which resembles a micro-beam framework. Although the two-dimensional design of the stereom has been studied, its spatial architecture is only little known. It is, however, imperative to understand the spatial architecture of the trabecular system in order to interpret its structural principles of this load-bearing construction. The echinoid’s trabecular system is thus analyzed in-depth with respect to eight topological descriptors. The echinoid’s plates are divided into two regions, the center of which consists of an unordered stereom, and the margin which consists of an ordered stereom. The eight trabecular descriptors indicate that the basal topology of the two plate regions are similar. The trabecular system predominantly consists of short and stocky trabeculae that show little tortuosity. The majority of trabeculae intersect in a 3N configuration, where three trabeculae intersect in one common node. Trabeculae in the 3N configuration intersect in an angle of around 120° resulting in a planar and triangular motif. These planar elements, when arranged in an angular off-set, can resist multi-dimensional loads. Results also show that the trabecular orientation perpendicular to the plate’s surface is at an angle of 60°. The trabecular orientation in the plate’s horizontal plane is directional. Both trabecular orientations reflect a construction which is capable of resisting applied loads and can distribute these loads over the entire skeleton. The spatial architecture of the echinoid’s trabecular system is thus considered to be a performative light-weight and load-bearing system.

Flexible sutures reduce bending moments in shells: from the echinoid test to tessellated shell structures

“…Visual survey, together with knowledge provided by the literature [8][9][10]14,15,[17][18][19][20][21]30,31,54], have highlighted four major functional features that contribute to the stability of the echinoid structure and influence its mechanical behaviour, namely: knob-like protrusions and collagenous ligaments, trivalent vertex arrangement of joints, curved geometry of plates and edges (figure 2c-f ).…”

“…It is composed of a series of skeletal plates joined by skeletal protrusions and collagenous sutures [8][9][10][11][12][13]. Each plate consists of highmagnesium calcite material arranged in a porous three-dimensional lattice-like meshwork (stereom) [14][15][16]. This design fulfils several mechanical and biological functional principles acting as a resistant, lightweight and load-bearing system adapted to withstand biotic (e.g.…”

Stereomic microstructure of Clypeasteroida in thin section based on new material from Pleistocene strata in Taiwan

“…μCT imaging is a non-destructive technique to visualize fossil urchins based on X-ray (Grun and Nebelsick 2018a). With the μCT-100X, the main advantage is that virtual thin-slices in any angles are possible based on the computed three-dimensional reconstruction, allowing a detail comparison with images of our thin sections.…”

“…1). Stereom studies are crucial to understand the phylogeny, growth, and soft tissue of the Echinoidea (Pearse and Pearse 1975;Seilacher 1979;Smith 1980Smith , 1984Smith , 1989Smith , 1991Ebert 2013;Grun and Nebelsick, 2018a, 2018b, 2018c.…”

<p class="HeadingRunIn"><strong>Combined visualization of echinoderm hard and soft parts using contrast-enhanced micro-computed tomography</strong></p>

“…As conventional µCT studies are based on the principle of X-ray attenuation, hard parts will usually be the primary focus of analysis. Following the pioneering study by Stock et al (2002), the capacity of µCT to accurately depict mineralized echinoderm tissues in 3D has so far been demonstrated in studies on extant crinoids (Aschauer et al 2010, Ziegler 2012, asteroids (Ziegler 2012, Ziegler & Menze 2013, Blowes et al 2017, Schwertmann et al 2019, ophiuroids (Ziegler 2012, Landschoff & Griffiths 2015, Okanishi et al 2017, Clark et al 2019, echinoids (Stock et al , 2004a(Stock et al , 2012Ziegler et al 2010a;Mihaljević et al 2011;Ziegler 2012;Ziegler & Menze 2013;Goetz et al 2014;Grun & Nebelsick 2018a, 2018bLauer et al 2018), and holothuroids (Reich 2015) as well as a diverse array of fossil echinoderm taxa (Rahman & Clausen 2009, Zamora et al 2012, Rahman et al 2015, Reid et al 2018. In addition, several high-resolution SRµCT studies (David et al 2009;Rahman & Zamora 2009;Stock et al 2004bStock et al , 2010Stock et al , 2013Stock et al , 2017Stock & Rack 2014;Ziegler et al 2010bZiegler et al , 2012aSouto & Martins 2018) as well as two clinical CT studies conducted using larger specimens (Martony et al 2018, ...…”