Mucron Explained

A mucron is an attachment organelle found in archigregarines - an order of epicellular parasitic Conoidasida.^{[1] [2]}

The mucron is derived from the apical complex, which is found in all members of the phylum Apicomplexa.^{[1] [3]}

The mucron is located at the anterior (apical) end of the cell and comprises the conoid, rhoptries, apical polar ring(s), and a large food vacuole (also called mucronal vacuole) having an outlet opening - a cytostome. It is used to attach and feed from the host's cell.^{[4] [5] [6]}

The epimerites of some aseptate eugregarines superficially (at the light microscopic level) resemble mucron and are usually called in the same way.^{[1] [3] [2]} This widespread misunderstanding originated from the conventional definition first proposed by Levine in 1971: "[the mucron is] an attachment organelle of aseptate gregarines. It is similar to an epimerite, but is not set off from the rest of the gregarine body by what appears under the light microscope to be a septum":^[7] thus, it may be equally applied to archigregarines and aseptate eugregarines as both they are aseptate. Note that the genuine epimerites are usually not separated by septa from the rest of the cell,^{[8] [9]} so this definition is misleading.^[2]

Notes and References

1. Book: Perkins FO, Barta JR, Clopton RE, Peirce MA, Upton SJ . Phylum Apicomplexa . Lee JJ, Leedale GF, Bradbury P . An Illustrated guide to the Protozoa: organisms traditionally referred to as protozoa, or newly discovered groups . Society of Protozoologists . 2nd . 2000 . 704052757 . 1891276220 . 190–369 . 1.
2. Simdyanov TG, Guillou L, Diakin AY, Mikhailov KV, Schrével J, Aleoshin VV. (2017) A new view on the morphology and phylogeny of eugregarines suggested by the evidence from the gregarine Ancora sagittata (Leuckart, 1860) Labbé, 1899 (Apicomplexa: Eugregarinida) PeerJ 5:e3354 https://peerj.com/articles/3354/?td=wk
3. Adl SM, Simpson AG, Lane CE, Lukeš J, Bass D, Bowser SS, Brown M, Burki F, Dunthorn M, Hampl V, Heiss A, Hoppenrath M, Lara E, leGall L, Lynn DH, McManus H, Mitchell EAD, Mozley-Stanridge SE, Parfrey LW, Pawlowski J, Rueckert S, Shadwick L, Schoch C, Smirnov A, Spiegel FW. (2012) The revised classification of eukaryotes. Journal of Eukaryotic Microbiology 59:429-514. https://doi.org/10.1111/j.1550-7408.2012.00644.x
4. Schrével J. (1971) Observations biologiques et ultrastructurales sur les Selenidiidae et leurs conséquences sur la systématique des Grégarinomorphes. Journal of Protozoology 18:448–479. https://doi.org/10.1111/j.1550-7408.1971.tb03355.x
5. Schrével J, Valigurová A, Prensier G, Chambouvet A, Florent I, Guillou L. (2016) Ultrastructure of Selenidium pendula, the type species of archigregarines, and phylogenetic relations to other marine Apicomplexa. Protist 167:339-368. https://doi.org/10.1016/j.protis.2016.06.001
6. Simdyanov TG, Kuvardina ON. (2007) Fine structure and putative feeding mechanism of the archigregarine Selenidium orientale (Apicomplexa: Gregarinomorpha). European Journal of Protistology 43:17-25. https://doi.org/10.1016/j.ejop.2006.09.003
7. Levine ND. (1971) Uniform terminology for the protozoan subphylum Apicomplexa. Journal of Protozoology 18:352-355. https://doi.org/10.1111/j.1550-7408.1971.tb03330.x
8. Book: Grassé, P.P. . M.C. . Caullery . Traité de zoologie: anatomie, systématique, biologie. Tome I, Fasc. II, Protozaires, rhizopodes, Actinopodes, Sporozoaires, Cnidosporidies . Masson et Cie . Paris . 1953 . 642231286 .
9. Desportes I, Schrével J. (2013) Treatise on Zoology - Anatomy, Taxonomy, Biology. The Gregarines. Leiden: Brill. https://doi.org/10.1163/9789004256057