Form and function of the mantle edge in Protobranchia (Mollusca: Bivalvia)
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Elsevier
Materia
Sarepta Acila Nucula Nuculana Lembulus Solemya Periostracum Valve crenulations Ennucula
Date
2022-06-28Referencia bibliográfica
Carmen Salas... [et al.]. Form and function of the mantle edge in Protobranchia (Mollusca: Bivalvia), Zoology, Volume 153, 2022, 126027, ISSN 0944-2006, [https://doi.org/10.1016/j.zool.2022.126027]
Sponsorship
Málaga/CBUAAbstract
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.