Marine Biology

, 164:64 | Cite as

Cuticle of Polyplacophora: structure, secretion, and homology with the periostracum of conchiferans

  • Antonio G. Checa
  • Michael J. Vendrasco
  • Carmen SalasEmail author
Original paper


The plesiomorphic state of the molluscan scleritome remains ambiguous. Chitons are significant because they show a mix of characters considered diagnostic in both aplacophorans and conchiferans, with both shell plates and small calcified girdle elements on an elongate body, and there is no consensus on the homology of structures involved in chiton plate calcification with those in conchiferan shells. Using light, scanning, and transmission microscopy, the present study examined the structure and formation of the cuticle and underlying epithelium in five chiton species collected over several years in southeast Spain and in California, USA. The cuticular matrix in chitons is similar to the translucent layer of the bivalve periostracum, although there are differences in the orientation of the densely spaced laminae with respect to the mantle surface. The cuticle arises in the accessory fold of the ventral girdle mantle. There is full continuity between the outermost layer of the cuticle and the thin outer layer of the tegmentum, suggesting that the latter is derived from the cuticular wedge permanently lying on the plate margins. A homology is proposed between the cuticle/associated girdle mantle epithelium of Polyplacophora and the periostracum/inner side of the outer mantle fold of the Bivalvia. Nevertheless, while the bivalve periostracum slides over the mantle epithelium during growth, the polyplacophoran cuticle remains stationary. The configuration of the cuticle, which overlaps the plate margins, allows it to efficiently close the plate biomineralization compartment, in a way comparable to that of the periostracum of conchiferans.


Chitons Cuticle Shell formation Homology Biomineralization Periostracum 



Special thanks are given to Douglas J. Eernisse (Department of Biological Science, California State University, CA, USA) for the donation of dried specimens of Lepidozona pectinulata and Serge Gofas (Department of Animal Biology, University of Málaga, Spain), for sampling the Spanish Mediterranean species. We also thank Eva M. Enjuto (Andalusian Center of Nanomedicine and Biotechnology [BIONAND], Málaga) for embedding some specimens in methacrylate. Funding to AC, MV, and CS was provided by Research Projects CGL2013-48247-P of the Spanish Ministerio de Economía y Competitividad (MINECO) and Fondo Europeo de Desarrollo Regional (FEDER). Additional funds were obtained from the Marie Curie International Incoming Fellowship (IIF 301668) (to MV and AC), and by the Research Group RNM363 (Andalusian Consejería de Economía, Investigación, Ciencia y Empleo, of the Junta de Andalucía) (to AC).

Compliance with ethical standards

This study followed all applicable international, national, and institutional guidelines for the collection and use of animals.

Conflict of interest

The coauthors Antonio G. Checa, Michael Vendrasco and Carmen Salas declare they have no conflicts of interest.


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Authors and Affiliations

  1. 1.Departamento de Estratigrafía y PaleontologíaUniversidad de GranadaGranadaSpain
  2. 2.Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de GranadaArmillaSpain
  3. 3.Department of GeologyPasadena City CollegePasadenaUSA
  4. 4.Departamento de Biología Animal, Facultad de CienciasUniversidad de MálagaMálagaSpain

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