Pinacocyte

Pinacocytes are flattened cells that cover the external surface and line portions of the internal canal system of sponges. Pinacocytes are key to protect and maintain the structure of the sponge, as well play a critical role in signaling, contraction, phagocytosis, and regulation of water flow. Pinacocytes can be broken down into three main types. Exopinacocytes found on the other surface, endopinacytes which line internal canals, and basipinacocytes which are key for contraction.

Structure and Morphology

Pinacocytes are thin, flattened cells whose unique morphology and structure allow them to form a protective layer along sponge surfaces similar to epithelia in vertebrates. Depending on location of the pinacocytes their structure can change.

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Function

Pinacocytes are part of the epithelium in sponges. Pinacocytes contribute to several physiological processes in sponges, including contraction, signaling, phagocytosis, and regulation of the internal environment. Pinacocytes can coordinate contraction to alter the diameter of canals and help expel water from the sponge. Pinacocytes form the outer cell boundary enclosing the mesohyl which is a gel like substance that helps maintain the shape and structure of the sponge.

Types of Pinacocytes

Pinacocytes are classified into different types according to their location and role within the sponge body. Types include: Basipinacocytes, Exopinacocytes, and Endopinacocytes

Basipinacocytes

These are the cells in contact with the sponge's substrate (the surface to which it is attached).

Exopinacocytes

These are found on the exterior of the sponge. Exopinococytes produce spicules which is a needle like process that serves as structure for the organism.

Endopinacocytes

These line the sponge's interior canals.

Development and Differentiation

Pinacocytes arise through cellular differentiation from stem and progenitor cells and are part of sponges’ cell renewal process.

Evolutionary Significance

The characteristics of pinacocytes have made them a target for investigating the evolutionary steps modern day epithelia has been through.

References

  1. 1 2 Sogabe, Shunsuke; Hatleberg, William L.; Kocot, Kevin M.; Say, Tahsha E.; Stoupin, Daniel; Roper, Kathrein E.; Fernandez-Valverde, Selene L.; Degnan, Sandie M.; Degnan, Bernard M. (June 2019). "Pluripotency and the origin of animal multicellularity". Nature. 570 (7762): 519–522. Bibcode:2019Natur.570..519S. doi:10.1038/s41586-019-1290-4. hdl:10023/19125. ISSN 0028-0836. PMID 31189954. S2CID 92562184.
  2. 1 2 3 4 >Leys, Sally P.; Grombacher, Lauren; Field, Daniel; Elliott, Glen R. D.; Ho, Vanessa R.; Kahn, Amanda S.; Reid, Pamela J.; Riesgo, Ana; Lanna, Emilio; Bobkov, Yuriy; Ryan, Joseph F.; Horton, April L. (2025-02-14). "A morphological cell atlas of the freshwater sponge Ephydatia muelleri with key insights from targeted single-cell transcriptomes". EvoDevo. 16 (1) 1. doi:10.1186/s13227-025-00237-7. ISSN 2041-9139. PMC 11827373. PMID 39953556.
  3. 1 2 >Leys, Sally P.; Hill, April (2012), "The Physiology and Molecular Biology of Sponge Tissues", Advances in Marine Biology, 62, Elsevier: 1–56, doi:10.1016/B978-0-12-394283-8.00001-1, ISBN 978-0-12-394283-8, PMID 22664120, retrieved 2026-09-22{{citation}}: CS1 maint: work parameter with ISBN (link)
  4. ↑ "28.1: Phylum Porifera". Biology LibreTexts. 2015-11-02. Retrieved 2020-12-03.
  5. 1 2 >Elliott, Glen R. D.; Leys, Sally P. (2007-11-01). "Coordinated contractions effectively expel water from the aquiferous system of a freshwater sponge". Journal of Experimental Biology. 210 (21): 3736–3748. Bibcode:2007JExpB.210.3736E. doi:10.1242/jeb.003392. ISSN 1477-9145. PMID 17951414.
  6. ↑ Müller, Werner E.G. (August 2006). "The stem cell concept in sponges (Porifera): Metazoan traits". Seminars in Cell & Developmental Biology. 17 (4): 481–491. doi:10.1016/j.semcdb.2006.05.006. PMID 16807004.
  7. ↑ Doerr, Sophia; Zhou, Phillip; Ragkousi, Katerina (February 2024). "Origin and development of primary animal epithelia". BioEssays. 46 (2) 2300150. doi:10.1002/bies.202300150. ISSN 0265-9247. PMC 11164562. PMID 38009581.