Fig 1
Arbacia punctulata (Echinoidea: Arbacioida). Major internal soft tissue structures of a "regular" sea urchin. Modified after Coe (1912).
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Echinoidea (sea urchins) are a group of benthic marine invertebrates that belong to the deuterostome taxon Echinodermata. Although extensive data have been gathered on larval and adult hard-part anatomy of sea urchins, for several reasons the knowledge of echinoid soft tissue anatomy is still fragmentary. For example, published works report differe...
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... are characterized by the presence of the radial canals of the water vascular system, whereas the interambulacra give rise to the reproductive organs. The major internal soft tissue structures include the dominant alimentary canal, reproductive organs, the various muscles of Aristotle's lantern, the water vascular system, and the axial complex ( Fig. 1). ...
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... experiments were conducted at the Berlin Neuroimaging Center at 7 Tesla ( 1 H-resonance- frequency 300 MHz) using a Bruker Pharmascan 70/16 AS (Bruker Biospin, Ettlingen, Germany) ( Fig. 1). The system consisted of a 160 mm horizon- tal bore magnet and a shielded gradient set with an inner diameter of 90 mm and a maximum gradient strength of 300 mT/m. A commercial linear 1 H- radio-frequency volume resonator with an inner di- ameter of 38 mm was used for excitation and for the detection of signal intensity. The images ...
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... analysis showed that although slight differences in anatomical makeup did occur, localization, arrangement and overall shape of the internal organs did not differ significantly. In the specimens depicted ( Figure 1A and 1B), this is exemplified by the almost identical shapes of both Aristotle's lanterns and the localization and shape of the digestive tract components. The structure of the wall of the sea urchin lower gut loop (also termed the stomach) was undulated in both specimens, whereas the horizontal sections of the upper gut loop (also termed the intestine) showed a smooth structure. ...
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... structure of the wall of the sea urchin lower gut loop (also termed the stomach) was undulated in both specimens, whereas the horizontal sections of the upper gut loop (also termed the intestine) showed a smooth structure. The digestive tract of one specimen was partly filled ( Figure 1A), while the digestive tract of the other specimen was empty, apart from tiny objects ( Figure 1B). Another striking similarity was the almost exactly identical location of the inner and outer marginal sinus of the haemal system in both speci- mens. ...
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... structure of the wall of the sea urchin lower gut loop (also termed the stomach) was undulated in both specimens, whereas the horizontal sections of the upper gut loop (also termed the intestine) showed a smooth structure. The digestive tract of one specimen was partly filled ( Figure 1A), while the digestive tract of the other specimen was empty, apart from tiny objects ( Figure 1B). Another striking similarity was the almost exactly identical location of the inner and outer marginal sinus of the haemal system in both speci- mens. ...
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... next set of experiments served to assess the effects of a gadolinium-based contrast agent (Magnevist, a standard in clinical and pre-clinical MRI studies) on image quality. Using the same specimen of P. miliaris and the same imag- ing protocol, we found that the application of the contrast agent resulted in enhanced contrast, although some thin- walled structures, such as the ampullae or the oesophagus, became less visible ( Figure 1C and 1D). Another advan- tage of the use of this contrast agent was that some of the artefacts caused by paramagnetic gut content were reduced due to the stronger water signal. ...
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... the dis- sections, MRI experiments using freshly fixed and museum specimens of P. miliaris were carried out. Struc- tures visible in the freshly fixed specimen ( Figure 1E) were recognizable also in the 135-year-old museum specimen ( Figure 1F). The size and location of the anatomical fea- tures varied slightly, but this had been observed among different specimens of freshly fixed animals as well. ...
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... the dis- sections, MRI experiments using freshly fixed and museum specimens of P. miliaris were carried out. Struc- tures visible in the freshly fixed specimen ( Figure 1E) were recognizable also in the 135-year-old museum specimen ( Figure 1F). The size and location of the anatomical fea- tures varied slightly, but this had been observed among different specimens of freshly fixed animals as well. ...
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... sediment component is causing which type of artefact needs to be determined in mineralogical studies on freshly fixed specimens. The effects of the contrast agent made it possible to reduce the negative effects of these artefacts in some cases ( Figure 1C and 1D), but a thor- ough investigation of the potential of selective and non- selective contrast agents [44] is essential for their future application in invertebrate morphology. Other major sources for artefacts were the tendency of spatangoid sea urchins to accumulate ferric iron phosphate in the con- nective tissues of their digestive tracts [45], and the diges- tive tract diverticula of scutelline sand dollars known to harbour magnetite [46]. ...
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... for some organs high intraspecific variability was detected, in particular in the case of organs with a development-dependent size and shape such as the gonads ( Figure 1E and 1F), shape and localization of other organs (for example the digestive tract) did not dif- fer significantly among specimens from a given echinoid species, allowing comparison on various taxic levels (Fig- ures 3 and 4). However, intraspecific variability of internal organs can also be observed in other taxa, for example gas- tropods (sinistral freak) or humans (situs inversus vis- cerum). ...
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... a traditional article, the following would be typical of how the structural information is presented to the reader: the heterotrimer consists of HC, b 2 m and the self-peptide pVIPR (Figure 1). Although the ends of pVIPR [peptide residues 1 (p1) and p2, and p8 and p9] are bound identically in both conformations, the middle of the peptide (p3 to p7) diverges considerably. ...
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... the ends of pVIPR [peptide residues 1 (p1) and p2, and p8 and p9] are bound identically in both conformations, the middle of the peptide (p3 to p7) diverges considerably. This is a consequence of the pre- sence of the HC residue Asp116 (coloured red in Figure 1b- d), which binds to pArg5 by a bidentate salt bridge (yellow in Figure 1b,d) in one of the conformations. In this binding mode (termed non-canonical or p6a; coloured magenta in Figure 1), the main chain w and c torsion angles occur in a- helical conformation only at p6, whereas, in the other, conventional peptide-binding mode (termed p4a; coloured light blue in Figure 1), this is the case only at p4. ...
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... the ends of pVIPR [peptide residues 1 (p1) and p2, and p8 and p9] are bound identically in both conformations, the middle of the peptide (p3 to p7) diverges considerably. This is a consequence of the pre- sence of the HC residue Asp116 (coloured red in Figure 1b- d), which binds to pArg5 by a bidentate salt bridge (yellow in Figure 1b,d) in one of the conformations. In this binding mode (termed non-canonical or p6a; coloured magenta in Figure 1), the main chain w and c torsion angles occur in a- helical conformation only at p6, whereas, in the other, conventional peptide-binding mode (termed p4a; coloured light blue in Figure 1), this is the case only at p4. ...
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... is a consequence of the pre- sence of the HC residue Asp116 (coloured red in Figure 1b- d), which binds to pArg5 by a bidentate salt bridge (yellow in Figure 1b,d) in one of the conformations. In this binding mode (termed non-canonical or p6a; coloured magenta in Figure 1), the main chain w and c torsion angles occur in a- helical conformation only at p6, whereas, in the other, conventional peptide-binding mode (termed p4a; coloured light blue in Figure 1), this is the case only at p4. In both conformations, the other w/c torsion angles, respectively, are as in b-strands. ...
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... is a consequence of the pre- sence of the HC residue Asp116 (coloured red in Figure 1b- d), which binds to pArg5 by a bidentate salt bridge (yellow in Figure 1b,d) in one of the conformations. In this binding mode (termed non-canonical or p6a; coloured magenta in Figure 1), the main chain w and c torsion angles occur in a- helical conformation only at p6, whereas, in the other, conventional peptide-binding mode (termed p4a; coloured light blue in Figure 1), this is the case only at p4. In both conformations, the other w/c torsion angles, respectively, are as in b-strands. ...
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... 2D images shown in Figure 1a,d provide the reader with a general idea of the structure of the HLA-B*2705- pVIPR complex, as would be typical for any other 3D structure presented in an academic paper. A surface representation of the entire molecule is shown in Figure 1a, followed by a view of the binding groove with pVIPR in both binding modes (Figure 1b, semi-transpar- ent surface and cartoon representation). ...
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... 2D images shown in Figure 1a,d provide the reader with a general idea of the structure of the HLA-B*2705- pVIPR complex, as would be typical for any other 3D structure presented in an academic paper. A surface representation of the entire molecule is shown in Figure 1a, followed by a view of the binding groove with pVIPR in both binding modes (Figure 1b, semi-transpar- ent surface and cartoon representation). The bidentate salt bridge between HC Asp116 and pArg5 that charac- terizes the p6a-binding mode is also shown. ...
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... 2D images shown in Figure 1a,d provide the reader with a general idea of the structure of the HLA-B*2705- pVIPR complex, as would be typical for any other 3D structure presented in an academic paper. A surface representation of the entire molecule is shown in Figure 1a, followed by a view of the binding groove with pVIPR in both binding modes (Figure 1b, semi-transpar- ent surface and cartoon representation). The bidentate salt bridge between HC Asp116 and pArg5 that charac- terizes the p6a-binding mode is also shown. ...
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... bidentate salt bridge between HC Asp116 and pArg5 that charac- terizes the p6a-binding mode is also shown. Finally, Figure 1c,d demonstrate that an omission of HC, b 2 m and one of the peptide conformations leads to an unob- structed, simplified view of the remaining pVIPR-binding mode. Representations like these provide the bare mini- mum of information that must be available for an evalu- ation of the structure of a molecule. ...
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... in Biochemical Sciences Vol.33 No.9 publication, Figure 1 would therefore have to be comple- mented by several additional images providing more structural detail (see, e.g. Ref. [10]). ...
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... alternative and more enlightening approach that we advocate here involves the use of the freely available Adobe Reader (Version 7.1 or later) to access the 3D model of the molecule in an interactive manner -this is achieved by clicking on any part of Figure 1 in the interactive PDF version of this publication (see Supple- mentary Material online). An introduction into the pos- sibilities that are offered is provided when the 'Help' option within the program is addressed. ...
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... model was saved in the Adobe Universal 3D file format, which was then opened in Adobe Acrobat 3D. The four images shown in Figure 1a-d were created from TIFF-format desktop screenshots of the desired model views and were modified in Adobe Photoshop CS3 to show the desired information (i.e. cropped to size). ...
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... Adobe Reader (www.adobe.com/products/reader/productinfo/systemreqs). (Figure 1a-d) of the HLA-B*2705- pVIPR complex. Note: the processes on the left of the flow chart are ones that will hopefully become redundant in the future if the Adobe Acrobat 3D software is ever updated to be able to perform these tasks itself. ...
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... program was also used to assign additional features of the model, such as its rendering mode or lighting. The 2D representations in Figure 1a-d were also created during this stage. The last step consisted of preparing and designating the preset views for the reader. ...
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... should be noted that the Adobe Acrobat 3D Toolkit enables authors to incorporate many more features into 3D models, such as the labelling of components of the structure, measuring distances, variable lighting options and several additional model-render modes. We have deliberately limited the options that are available in the model presented here to enable the reader to concentrate on the principal features that distinguish the conventional 2D representations of Figure 1a-d from the PDF-inte- grated 3D models of the molecular structures. These are the 3D-viewing capability, platform-independence, acces- sibility and, probably of greatest importance, its interac- tivity that enables the reader to delve into aspects of the structure that would otherwise not be available to them readily. ...
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... in Biochemical Sciences Vol.33 No.9 Supplementary data Owing to the necessity to provide a standard-format PDF to institutions for their archives, this version of the article cannot currently include the interactive Figure 1. Instead, the fully interactive version of this article is available as Supplementary material ...
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... The structurally most divergent axial complex can be observed in the highly derived Atelostomata in which the reorganization of the digestive tract is most pronounced. Our findings demonstrate a structural interdependence of various internal organs, including digestive tract, mesenteries, and the axial complex. Sea urchins (Echinoidea) -see Fig. 1 for the present view on sea urchin phylogeny based largely on hard-part morphology and molecular data -also possess a well-developed axial complex. The morphological data obtained for this structure are based to a large extent on findings in the more easily accessible "regular" sea urchins such as Arbacia punctulata, Psammechinus ...
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... specimens referred to in this study are listed in Table 1 together with information on the current systematic classification of each species (see also Fig. 1), the source of the data used in the study, specimen ID where applicable, and literature ...
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... (2005), Stockley et al. (2005), andSmith et al. (2006). Sea cucumbers (Holothuroi- dea) constitute the sister taxon to sea urchins, while Cidaroida are the most primitive taxon within the Echinoidea and sister taxon to Euechinoidea. The "Regularia" are a paraphyletic clade, while the Echinacea and the Irregularia each form a monophyletic taxon (Fig. ...
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... latter is lined by a ciliated epithelium as well. The diameter of the madreporic ampulla becomes gradually smaller towards its adoral end and it basally diverges into stone canal and axial coelom. The dorsal sac lies laterally underneath the madreporic ampulla and sur- rounds the globular head process (Figs. 8, 11A). The dorsal sac is a closed cavity and is not connected to either madreporic ampulla, stone canal or the axial coelom. Boolootian & Campbell (1964), however, report a divergent morphology of the dorsal sac in Strongylo- centrotus purpuratus in which the dorsal sac communicates with the somatocoel via a small slit and is divided into ...
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... Psammechinus miliaris, a ciliated, pseudostratified monolayer lines the dorsal sac (Fig. 10A). While only some of the peripheral lining cells are epithelio-muscle cells, those rest- ing on the matrix of the head process form a strong myoepithelium (Fig. 11E). Here, the epithelio-muscle cells contain strong, basally located bundles of myofilaments that form a regular network of rectangularly arranged outer circular and inner ...
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... Psammechinus miliaris, a ciliated, pseudostratified monolayer lines the dorsal sac (Fig. 10A). While only some of the peripheral lining cells are epithelio-muscle cells, those rest- ing on the matrix of the head process form a strong myoepithelium (Fig. 11E). Here, the epithelio-muscle cells contain strong, basally located bundles of myofilaments that form a regular network of rectangularly arranged outer circular and inner longitudinal bundles that are embedded in the voluminous matrix of the head process. The perikarya deeply extend into the dorsal sac lumen, which indicates that the ...
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... axial organ begins at the level of the first curvature of the oesophagus and is sur- rounded by numerous haemal lacunae (Fig. 11B). That part of the axial organ which bulges into the axial coelom contains numerous deep crypts and invaginations in Psammechinus miliaris, so that the axocoelomic surface of the axial organ is tremendously enlarged. Inside the canaliculi, the entire lumen seems to be occupied by microvilli (Fig. 10B). Only a few cells are found inside ...
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... and is sur- rounded by numerous haemal lacunae (Fig. 11B). That part of the axial organ which bulges into the axial coelom contains numerous deep crypts and invaginations in Psammechinus miliaris, so that the axocoelomic surface of the axial organ is tremendously enlarged. Inside the canaliculi, the entire lumen seems to be occupied by microvilli (Fig. 10B). Only a few cells are found inside the lumen, most of them coelomocytes. Haemotocytes at different stages of differentiation are present within the matrix. They contain residual bodies and lysosomes of different ...
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... podocytes rest on the axial coelomic side of the matrix (Figs. 10C, 11F). Their pedicels are bridged by electron-dense diaphragmata. Each podocyte has a single cilium with a (9x2)+2 axoneme that adheres to the cell body by a basal body, short rootlets and an accessory centriole perpendicular to the basal body. A circle of 9-12 strong microvilli surrounds each cilium (Fig. 10D). Additional microvilli ...
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... axial coelomic side of the matrix (Figs. 10C, 11F). Their pedicels are bridged by electron-dense diaphragmata. Each podocyte has a single cilium with a (9x2)+2 axoneme that adheres to the cell body by a basal body, short rootlets and an accessory centriole perpendicular to the basal body. A circle of 9-12 strong microvilli surrounds each cilium (Fig. 10D). Additional microvilli emanate from the surface of the perikaryon and only seldom from the pedicels. In Echinometra sp., the podocytes within the axial coelom lining are irregularly distributed and not restricted to the side covering the axial organ (Welsch & Rehkämper ...
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... stone canal lining in Psammechinus miliaris is a monolayered columnar epithelium (Fig. 11C). Each of these epithelial cells bears a long cilium with a (9x2)+2 axomene that adheres to the cell body with a basal body and three rootlet structures. A circle of 9-12 strong microvilli surrounds each cilium and additional smaller microvilli emanate from the cell surface. A number of glandular cells that show a distinct polarity can ...
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... apex while other cellular components are located more basally. However, degrading cells can rarely be found among the basal portions of the lining cells, and epithelio-muscle cells, muscle cells or podocytes were never seen to be part of the stone canal epithelium. The somatocoel is lined by a flat epithelium which is only slightly muscularized (Figs. 10D, 11D). The cilia of the somatocoel epithelium show the characteristic composition with a dense microvilli fringe surrounding the axoneme. The epithelial cells are connected to each other via adhaerens junctions and do not show the specializations of the dorsal sac and axial coelom ...
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... foot anchor the cilium to the cell. Both ciliary rootlets are co-axial, running obliquely to the main axis of the basal body. Some fibrillar material secures the connection of the accessory centriole to the longer vertical rootlet and fixes its position underneath the basal foot. The cilia are encircled by a dense fringe of 9-12 strong microvilli (Fig. 10E). Numerous podocytes line the axial coelom and the lumina of the canaliculi inside the axial organ (Fig. 11F). The canaliculi are filled with a huge number of microvilli and cilia that project into their lumen, resulting in a tremen-dous surface extension (Fig. 10F). Epithelio-muscle cells can be detected sporadically, and sometimes ...
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... the basal body. Some fibrillar material secures the connection of the accessory centriole to the longer vertical rootlet and fixes its position underneath the basal foot. The cilia are encircled by a dense fringe of 9-12 strong microvilli (Fig. 10E). Numerous podocytes line the axial coelom and the lumina of the canaliculi inside the axial organ (Fig. 11F). The canaliculi are filled with a huge number of microvilli and cilia that project into their lumen, resulting in a tremen-dous surface extension (Fig. 10F). Epithelio-muscle cells can be detected sporadically, and sometimes even podocytes seem to bear muscle ...
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... basal foot. The cilia are encircled by a dense fringe of 9-12 strong microvilli (Fig. 10E). Numerous podocytes line the axial coelom and the lumina of the canaliculi inside the axial organ (Fig. 11F). The canaliculi are filled with a huge number of microvilli and cilia that project into their lumen, resulting in a tremen-dous surface extension (Fig. 10F). Epithelio-muscle cells can be detected sporadically, and sometimes even podocytes seem to bear muscle ...
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... axial organ consists of a dense matrix and is rich in canaliculi and lacunae ( (Fig. 11D), consisting of a monociliated monolayer overlying the basal lamina of the axial organ. No podocytes could be detected in the somatocoelomic ...
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... Other irregular sea urchin taxa such as the Holectypoida, "Cassiduloida" and Clypeasteroida have obviously preserved the more plesio- morphic state, exhibiting an axial complex that is comparable in its gross morphology to the condition observed in Aspidodiadematidae or Salenioida, the taxa most closely associated with the ancestor of Irregularia (Fig. ...
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... prominent, in cross-section C-shaped dorsal sac (Figs. 2, 5, 11) is partially enveloping the head process in most species. According to , this structure is reduced in Schizaster canaliferus. Hamann (1887) and Wagner (1903), however, presented drawings of the dorsal sac and head process in Echinocardium mediterraneum and Hetero- brissus niasicus, which, together with the comparison of the axial ...
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... axial coelom of all species studied ends blindly at the adoral end of the axial organ (Figs. 2, 11). The axial coelom, like dorsal sac and madreporic ampulla, shows a similar structural pattern within the "regular" sea urchin species as well as the clypeasteroid spe- cies examined so far, although it must be noted that species of Atelostomata appear again to display a differing condition (see, e.g. ...
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... columnar epithelium of the stone canal is a distinctive feature in comparison to the flat epithelia of axial coelom and somatocoel (Fig. 11). The interior of the stone canal is filled with numerous cilia that cause an active and directed transport of coelomic fluid (Ludwig 1890, Rehkämper & Welsch 1988, Ferguson 1996. Another difference to the other coelomic cavities can be seen in the presence of glandular cells, which Rehkämper & Welsch (1988) consider to be ...
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... are present, the aboral sinuses are discreet. The lantern protractor muscles are smooth, longitudinal body wall muscles are absent, compass elevator muscles are present. The perioesophageal haemal system consists of a spongy ring; a collateral duct of the digestive tract haemal system is absent. The primary spines are not covered with epidermis. Fig. 1 depicts selected internal views. The oesophagus is short and straight, a primary siphon could not be detected. The presence of a siphonal groove is known for some taxa, a secondary siphon is generally absent. The smooth-walled stomach and intestine make a full turn each. An intestinal caecum could not be detected as well as Gregory's ...
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... a siphonal groove is absent. No secondary siphon can be found in arbaciids. A small caecum marks the beginning of the stomach. Compass elevator muscles are present, longitudinal body wall muscles are absent. The peri- oesophageal haemal system consists of five spongy bodies; a collateral duct is present. All spines are covered with epidermis. Fig. 12 depicts selected internal views. complex is straight in lateral view; the axial organ is oriented vertically. A peripharyngeal coelom surrounds Aristotle's lantern; buccal sacs are present and well-developed. Stewart's organs are entirely missing. The aboral sinuses are discreet. Five gonads are present. The structure of the lantern ...
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... are discreet. Five gonads are present. The structure of the lantern protractor muscles can be smooth or frilled. Compass elevator mus- cles are present, longitudinal body wall muscles are absent. The perioesophageal haemal system consists of five spongy bodies; a well-developed collateral duct is present. All spines are covered with epidermis. Fig. 13 depicts selected internal views. ...
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... spines are covered with epidermis. Fig. 15 depicts selected internal views. Compass elevator muscles are present, longitudinal body wall muscles are absent. The peri- oesophageal haemal system consists of five spongy bodies; a well-developed collateral duct is present. All spines are covered with epidermis. Fig. 16 depicts selected internal views. Trigonocidarids possess a ...
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... spines are covered with epidermis. Fig. 15 depicts selected internal views. Compass elevator muscles are present, longitudinal body wall muscles are absent. The peri- oesophageal haemal system consists of five spongy bodies; a well-developed collateral duct is present. All spines are covered with epidermis. Fig. 16 depicts selected internal views. Trigonocidarids possess a cylindrical to flattened digestive tract; the stomach as well as the intestine are both only slightly festooned. The oesophagus is rather short. A thin-walled primary siphon is present; a siphonal groove is presumably absent. No secondary siphon can be found in this taxon. A ...
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... this taxon. A small caecum marks the beginning of the stomach. Stomach of the lantern protractor muscles is smooth. Compass elevator muscles are present, longitudinal body wall muscles are absent. The perioesophageal haemal system consists of five spongy bodies; a well-developed collateral duct is present. All spines are covered with epidermis. Fig. 19 depicts selected internal views. Longitudinal body wall muscles are absent, compass elevator muscles are present in juvenile specimens. The peripharyngeal haemal system is not differentiated. A collateral duct of the digestive tract haemal system is absent. All spines are covered by an epidermis. Cassidulids possess a cylindrical ...
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... contrast to MRI, µCT studies using conventional scanners and established protocols lack the potential to display soft tissue structures (Fig. 1). This applies especially to sea urchins, where the strong X-rays have to penetrate the calcite endoskeleton twice, making the analysis of soft tissues in this taxon with conventional desktop µCT equipment practically impossible. However, more advanced CT methods such as synchrotron radiation tomography and very-high-resolution X-ray ...
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Citations
... , DeRidder and Brigmon (2003),Ziegler (2008),Ziegler et al. (2010), ...
A thorough understanding of the sea urchin (Echinodermata: Echinoidea) digestive tract anatomy is a prerequisite for the correct interpretation of physiological and biomechanical analyses focusing on the gut architecture of this ecologically important group of marine invertebrates. A number of studies have addressed the general arrangement of the sea urchin digestive tract, but accessory structures such as siphons and caeca have received less attention. Two studies carried out to analyze the gut physiology of various marine invertebrates briefly mentioned the presence of a previously undescribed pouch in the posterior digestive tract of the heart urchin (Echinoidea: Spatangoida) species Brisaster latifrons. Dissections, histological, and magnetic resonance imaging data, as well as three-dimensional reconstructions corroborate these findings. The novel structure—here termed the intestinal caecum—is suspended by a thin mesentery within a coil formed by the posteriormost part of the intestine. The kidney-shaped organ constitutes a derivative of the intestine, to which it is laterally connected through a narrow canal. In contrast to the sediment-packed main digestive tract, the intestinal caecum is filled with liquid and a flocculent mass. The organ’s histology is characterized by a thin connective tissue layer with only a small number of hemal lacunae and muscle fibers, as well as an inner simple columnar epithelium that contains numerous dark-brown vacuoles. The intestinal caecum is found exclusively among members of the Schizasteridae (Spatangoida: Paleopneustina). Specifically, the organ is present in selected species of the genera Abatus, Brisaster, and Tripylaster, but not in the other seven schizasterid genera analyzed. The intestinal caecum is not homologous to the sometimes equally named accessory structure present in the posterior digestive tract of other spatangoid taxa such as Echinocardium or Heterobrissus. Consequently, the previously introduced term recto-intestinal caecum is here applied for this latter organ. No correlation could be found between the absence or presence of the intestinal caecum and any known biological or morphological characteristics of schizasterid heart urchins. The distribution of the organ among schizasterids supports a close relationship of the genera Brisaster, Tripylaster, and selected species of Abatus.
... Furthermore, Figures 3, 4, 5, 6, 7, 8 denote whether the specimen is viewed aborally (AB), laterally (LA), or orally (OR). Figure 9 provides an overview of the general sea urchin digestive tract morphology - the models presented in this figure are entirely based on 3D MRI datasets [25,30]. Finally, Figure 10 provides three interactive 3D models of the digestive tracts of selected taxa. ...
The digestive tract of many metazoan invertebrates is characterized by the presence of caeca or diverticula that serve secretory and/or absorptive functions. With the development of various feeding habits, distinctive digestive organs may be present in certain taxa. This also holds true for sea urchins (Echinodermata: Echinoidea), in which a highly specialized gastric caecum can be found in members of a derived subgroup, the Irregularia (cake urchins, sea biscuits, sand dollars, heart urchins, and related forms). As such a specialized caecum has not been reported from "regular" sea urchin taxa, the aim of this study was to elucidate its evolutionary origin.
Using morphological data derived from dissection, magnetic resonance imaging, and extensive literature studies, we compare the digestive tract of 168 echinoid species belonging to 51 extant families. Based on a number of characters such as topography, general morphology, mesenterial suspension, and integration into the haemal system, we homologize the gastric caecum with the more or less pronounced dilation of the anterior stomach that is observed in most "regular" sea urchin taxa. In the Irregularia, a gastric caecum can be found in all taxa except in the Laganina and Scutellina. It is also undeveloped in certain spatangoid species.
According to our findings, the sea urchin gastric caecum most likely constitutes a synapomorphy of the Euechinoidea. Its occurrence in "regular" euechinoids is linked to the presence of an additional festoon of the anterior stomach in ambulacrum III. Both structures, the additional festoon and the gastric caecum, are absent in the sister taxon to the Euechinoidea, the Cidaroida. Since the degree of specialization of the gastric caecum is most pronounced in the predominantly sediment-burrowing irregular taxa, we hypothesize that its evolution is closely linked to the development of more elaborate infaunal lifestyles. We provide a comprehensive study of the origin and evolutionary plasticity of a conspicuous digestive tract structure, the gastric caecum, in a major taxon of the extant invertebrate macrozoobenthos.
Lytoceratites together with Phylloceratites are often described as “conservative”. However, the origin and monophyly of lytoceratid
ammonites as well as their role in the evolution of all ammonites is under constant debate. In this work, the Lytoceratoidea investigated
on generic level for the presence of a septal lobe. Included into this investigation is the verification of relevant literature and the
registration of the collected literature in a database system. Furthermore material from public and private collections was studied.
The investigation reveals that all Lytoceratoidea are characterised by the presence of a septal lobe which constitutes their monophyly
(cp. Arkell et al., 1957). The septal lobe represents a consistent morphological character that appeared in the lowermost Jurassic and
is present in the uppermost Cretaceous members of Lytoceratoidea. It was noticed that the septal lobe appeared earlier in ontogeny and
was stronger developed in most of the stratigraphical younger representatives compared to Jurassic members (acceleration). In addition,
further characters have been investigated and tested for their phylogenetic significance. It turned out that most of these characters e. g.
whorl section, course and number of constrictions are homoplastic or highly variable within one genus. Finally, six characters (septal
lobe, parabolic ribs, fimbriation, shape of adult lateral lobe, primary suture, jaw type) have been kept for stratocladistic analyses.
With this method the phylogeny within the Lytoceratoidea was enlightened as far as possible. Within the family Lytoceratidae five
monophyletic subfamilies are retained : Ectocentritinae, Pleuroacanthinae, Lytoceratinae, Alocolytoceratinae and Megalytoceratinae.
The monophyly of the second family Tetragonitidae is based on the distribution of the quinque- and sixlobate primary suture line and
the development of a rhynchaptychus (Engeser & Keupp, 2002). Within the Tetragonitidae two subfamilies (Gaudryceratinae and
Tetragonitinae) and one tribus Gabbioceratini are retained. This work has been the first critical-systematical review for the whole group
within the last forty years. As a main result of this investigation fifteen genera have been excluded from Lytoceratoidea, seventeen
genera have been regarded as junior subjective synonyms. A sexual dimorphic couple is presented for Anagaudryceras (M) and
Anagaudryceras (Zelandites [m]) for the first time in addition to the two well known of Lytoceras (M). Thirty genera have been retained
as valid lytoceratid taxa. For some genera e. g. Lobolytoceras and Protetragonites the stratigraphic distribution has been extended
significantly. “Trachyphyllites” costatus is included into Analytoceras hermanni and represents a typical Lower Jurassic lytoceratid
member. It appears that the Lytoceratoidea are derived from psiloceratids at the Triassic-Jurassic-boundary as already stated by Guex
(1987).
The author assents the statement of Guex (1987) and regards the Lytoceratoidea as members of Ammonitina. Tetragonitidae are
derived from Protetragonites. Both taxa develop non-fimbriate ribs in contrast to contemporary lytoceratids. Protetragonites fraasi
from the Oxfordian (Upper Jurassic) represents the oldest member of that genus. Judging from the two characters sixlobate primary
suture and septal lobe, discussed above, Lytoceratoidea represent the most advanced ammonoid group.
In the second part of this thesis the functional significance of the septal lobe was investigated. It was planned to calculate the ratio of
chamber volume against its surface. For this purpose a Gaudryceras specimen in hollow preservation was scanned using computer
tomography at the “Bundesanstalt für Materialforschung und -prüfung” (Berlin). The ammonite was digitalised at “Konrad-Zuse-
Institut” (Berlin) using AM IRA®. Unfortunately, the resolution was too low for the project. The positive effect of the ratio of chamber
volume against its surface caused by the septal lobe can therefore only be assumed. It is supposed that the septal lobe increases the
efficiency of the hydrostatic apparatus.
Magnetic resonance imaging (MRI) is now considered a routine tool for comparative morphological imaging in small vertebrate model organisms. However, the application of high-resolution imaging protocols to visualize the anatomy of invertebrate organisms has not yet become a generally accepted tool among zoologists. Here, we describe MRI protocols that permit visualization of both the internal and the external anatomy of freshly fixed invertebrates and specimens from museum collections. The choice of protocols has been optimized to allow the assembly of the large numbers of datasets that are necessary for comparative morphological analyses. Although the primary focus of our work is on sea urchin internal anatomy, we also present results from a variety of other invertebrate taxa to demonstrate the principal feasibility of MRI studies to obtain anatomical information at high resolutions. Furthermore, we briefly describe procedures suitable for 3D modelling.
