Form and function of the mantle edge in Protobranchia (Mollusca: Bivalvia)

We analyzed, by optical and transmission electron microscopy, the morphology and function of the mantle edge, including the formation of the periostracum, of ten species of protobranchs. Five species from the order Nuculida, four species from the order Nuculanida and one species from the order Solemyida were studied. A second outer fold, which seems to function as a template for the internal marginal crenulations of the valves, is present in the crenulated species of Nucula. The minute non-crenulated Ennucula aegeensis shows the glandular basal cells displaced toward the periostracal groove, resembling a minute additional fold between the outer and middle folds. Intense secretion of glycocalyx, together with active uptake of particles, have been observed in the inner epithelium of the middle mantle fold and the whole epithelium of the inner mantle fold in all the studied species. Contrary to the rest of the bivalves, all the protobranchs analyzed have two basal cells involved in the formation of the external nanometric pellicle of the periostracum, a character that would support the monophyly of protobranchs. A three-layered pattern is the general rule for the periostracum in protobranchs, like for other bivalves. The presence of pouches of translucent layer inside the tanned dark layer under periostracal folds is characteristic of the species with a folded periostracum; its function is unclear but could give flexibility to the periostracum. The non-nacreous internal shell layer and the presence of translucent pouches under periostracal folds in Sarepta speciosa resemble those found in nuculanids. However, the free periostracum is rather similar to those of N. hanleyi and E. aegeensis, with a continuous vesicular layer. All the latter supports the inclusion of Sarepta in the order Nuculanida but could indicate either a basal lineage or that the translucent vesicular layer is an adaptive trait.Málaga/CBU

Form and function of the mantle edge in Protobranchia (Mollusca: Bivalvia)

We analyzed, by optical and transmission electron microscopy, the morphology and function of the mantle edge, including the formation of the periostracum, of ten species of protobranchs. Five species from the order Nuculida, four species from the order Nuculanida and one species from the order Solemyida were studied. A second outer fold, which seems to function as a template for the internal marginal crenulations of the valves, is present in the crenulated species of Nucula. The minute non-crenulated Ennucula aegeensis shows the glandular basal cells displaced toward the periostracal groove, resembling a minute additional fold between the outer and middle folds. Intense secretion of glycocalyx, together with active uptake of particles, have been observed in the inner epithelium of the middle mantle fold and the whole epithelium of the inner mantle fold in all the studied species. Contrary to the rest of the bivalves, all the protobranchs analyzed have two basal cells involved in the formation of the external nanometric pellicle of the periostracum, a character that would support the monophyly of protobranchs. A three-layered pattern is the general rule for the periostracum in protobranchs, like for other bivalves. The presence of pouches of translucent layer inside the tanned dark layer under periostracal folds is characteristic of the species with a folded periostracum; its function is unclear but could give flexibility to the periostracum. The non-nacreous internal shell layer and the presence of translucent pouches under periostracal folds in Sarepta speciosa resemble those found in nuculanids. However, the free periostracum is rather similar to those of N. hanleyi and E. aegeensis, with a continuous vesicular layer. All the latter supports the inclusion of Sarepta in the order Nuculanida but could indicate either a basal lineage or that the translucent vesicular layer is an adaptive trait.This research was funded by the projects CGL2017-85118-P and PID2020-116660GB-I00 of the Spanish Ministry of Economy, Industry and Competitiveness. Funding for open access charge has been provided by the University of Málaga/CBUA

La grabación sonora: un recurso pedagógico multidisciplinar para la reinterpretación de la Historia

Mediante el presente proyecto se ha pretendido abordar un nuevo acercamiento a la historia de la música, en tanto manifestación cultural, basado en una metodología de reciente creación que entronca directamente con los estudios sobre la praxis interpretativa. Para ello hemos profundizado en el correcto manejo de los software informáticos que permiten el análisis de estas fuentes sonoras (fundamentalmente visualizadores de ondas y editores de sonido). Como resultado, hemos constituido un grupo de trabajo abierto a profesores y alumnos, ubicado físicamente en la Facultad de Geografía e Historia de la UCM

INNOVASONORA: gestión de archivos sonoros, sonido inmersivo y realidad virtual en plataformas LMS

Memoria del proyecto de innovación docente "Innovasonora" (Curso 2021-2022

Early Stage Biomineralization in the Periostracum of the ‘Living Fossil’ Bivalve Neotrigonia

A detailed investigation of the shell formation of the palaeoheterodont ‘living fossil’ Neotrigonia concentrated on the timing and manufacture of the calcified ‘bosses’ which stud the outside of all trigonioid bivalves (extant and fossil) has been conducted. Electron microscopy and optical microscopy revealed that Neotrigonia spp. have a spiral-shaped periostracal groove. The periostracum itself is secreted by the basal cell, as a thin dark pellicle, becoming progressively transformed into a thin dark layer by additions of secretions from the internal outer mantle fold. Later, intense secretion of the internal surface of the outer mantle fold forms a translucent layer, which becomes transformed by tanning into a dark layer. The initiation of calcified bosses occurred at a very early stage of periostracum formation, deep within the periostracal groove immediately below the initialmost dark layer. At this stage, they consist of a series of polycyclically twinned crystals. The bosses grow as the periostracum traverse through the periostracal groove, in coordination with the thickening of the dark periostracal layer and until, upon reaching the mantle edge, they impinge upon each other and become transformed into large prisms separated by dark periostracal walls. In conclusion, the initial bosses and the external part of the prismatic layer are fully intraperiostracal. With later growth, the prisms transform into fibrous aggregates, although the details of the process are unknown. This reinforces the relationships with other groups that have the ability to form intraperiostracal calcifications, for example the unionoids with which the trigonioids form the clade Paleoheterodonta. The presence of similar structures in anomalodesmatans and other euheterodonts raises the question of whether this indicates a relationship or represents a convergence. The identification of very early calcification within an organic sheet has interesting implications for our understanding of how shells may have evolved.Coordinated Research Projects CGL2010-20748-C02-01 (AGC, EMH) and 02 (CS) (DGI, Spanish MICINN); the Research Group RNM363 (Consejería de Economía, Investigación, Ciencia y Empleo, Junta de Andalucía); and the FP7 COST Action TD0903 of the European Community

Form and function of the mantle edge in Protobranchia (Mollusca: Bivalvia).

We analyzed, by optical and transmission electron microscopy, the morphology and function of the mantle edge, including the formation of the periostracum, of ten species of protobranchs. Five species from the order Nuculida, four species from the order Nuculanida and one species from the order Solemyida were studied. A second outer fold, which seems to function as a template for the internal marginal crenulations of the valves, is present in the crenulated species of Nucula. The minute non-crenulated Ennucula aegeensis shows the glandular basal cells displaced toward the periostracal groove, resembling a minute additional fold between the outer and middle folds. Intense secretion of glycocalyx, together with active uptake of particles, have been observed in the inner epithelium of the middle mantle fold and the whole epithelium of the inner mantle fold in all the studied species. Contrary to the rest of the bivalves, all the protobranchs analyzed have two basal cells involved in the formation of the external nanometric pellicle of the periostracum, a character that would support the monophyly of protobranchs. A three-layered pattern is the general rule for the periostracum in protobranchs, like for other bivalves. The presence of pouches of translucent layer inside the tanned dark layer under periostracal folds is characteristic of the species with a folded periostracum; its function is unclear but could give flexibility to the periostracum. The non-nacreous internal shell layer and the presence of translucent pouches under periostracal folds in Sarepta speciosa resemble those found in nuculanids. However, the free periostracum is rather similar to those of N. hanleyi and E. aegeensis, with a continuous vesicular layer. All the latter supports the inclusion of Sarepta in the order Nuculanida but could indicate either a basal lineage or that the translucent vesicular layer is an adaptive trait

Semi thin sections through the mantle edge of <i>Neotrigonia</i> and details of the periostracal groove.

<p>A, C. <i>Neotrigonia gemma</i>. B, D. <i>Neotrigonia margaritacea</i>. Cr, forming crystals; DL, dark layer; IMF, inner mantle fold; MMF, middle mantle fold; OMF, outer mantle fold; Pa, pallial tentacle; PG, periostracal groove; Po, periostracum; TL, translucent layer.</p

Shell microstructures of <i>Neotrigonia</i>.

<p>A. Vertical fracture through the prismatic and nacre layers of <i>N. lamarckii</i>. B. Fracture through the shell of <i>N. lamarckii</i>, showing the different shell layers. C. Detail of the upper part of the prismatic layer of <i>N. lamarckii</i>. The individual prisms are separated by thick periostracal membranes. D, E. Views of the external shell surface of <i>N. lamarckii</i>. The periostracal surface is ornated with nanometric pimples, which continue on top of the bosses. The bosses appear in high relief due to retraction of the periostracum upon dehydration. F. View of the free periostracum of <i>N. gemma</i> showing the regular distribution of bosses. G. Detail of the free periostracum of <i>N. gemma</i>. Etching of bosses reveals that they are composed of crystalline sectors. H. Surface of the periostracum of <i>N. margaritacea</i>, with cropping out bosses. Its position in J is indicated. I. Detail of the free periostracum of <i>N. gemma</i>. Intensive etching reveals lineations within bosses. J. Surface of the periostracum of <i>N. margaritacea</i>. Note the existence of bosses within the periostracal flap. K. Surface of the shell of <i>N. lamarckii</i>. The outlines of the prisms underlying the periostracum are clearly noticeable. Note the strict correspondence between each prism and its associated boss. L. Similar situation close to a rib of <i>N. lamarckii</i>. There appear small-sized additional prisms, which do not bear a boss. M. Fracture through the shell of <i>N. margaritacea</i>. The fractured prisms show a typical fibrous aspect. N. Fracture through the columnar nacre of <i>N. margaritacea</i>, close to the external surface. O. Fracture through the sheet nacre of <i>N. margaritacea</i>, at the mid shell thickness. B, boss; GD, growth direction; N, nacre; Pr, prismatic layer; Po, periostracum.</p

Schematic diagram depicting the initiation and early growth of bosses within the periostracal groove.

<p>Bosses inititate at subcellular positions which are equally spaced comarginally along the outer mantle fold. Growth proceeds as the periostracum slides between the mantle folds by secretions of the outer mantle fold. Below each boss there is a reticulum formed by extensions of the underlying microvilli, which also migrates across the cells in coincidence with the boss. The time of initiation alternates between rows, with the formation of bosses labelled 1 and 2 in the left diagram and of boss 3 in the right diagram. B, boss; Emv, reticulate extensions of the microvilli; MMF, middle mantle fold; Mv, microvilli; OMF, outer mantle fold; Po, periostracum.</p

Living specimen of <i>Neotrigonia lamarckii</i>, with the extended foot.

<p>Living specimen of <i>Neotrigonia lamarckii</i>, with the extended foot.</p