A ''mucron'' is an attachment

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...

found in archigregarines - an order of epicellular parasitic

Conoidasida Conoidasida is a class of parasitic alveolates in the phylum Apicomplexa. The class was defined in 1988 by Levine and contains two subclasses – the coccidia and the gregarines. All members of this class have a complete, hollow, truncated c ...

.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 The mucron is derived from the

apical complex The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic Alveolata, alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex stru ...

, which is found in all members of the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Apicomplexa The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. T ...

.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 The mucron is located at the anterior (apical) end of the cell and comprises the

conoid In geometry a conoid () is a ruled surface, whose rulings (lines) fulfill the additional conditions: :(1) All rulings are parallel to a plane, the '' directrix plane''. :(2) All rulings intersect a fixed line, the ''axis''. The conoid is a ri ...

, rhoptries, apical polar ring(s), and a large food

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

(also called mucronal vacuole) having an outlet opening - a

cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuol ...

. It is used to attach and to feed from the host's cell.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.xSchrével 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.2016.06.001Simdyanov 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 The epimerites of some aseptate eugregarines superficially (at the light microscopic level) resemble mucron and are usually called in the same way. This widespread misunderstanding originated from the conventional definition first proposed by Levine in 1971: " he mucron isan 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":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 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,Desportes I, Schrével J. (2013) Treatise on Zoology - Anatomy, Taxonomy, Biology. The Gregarines. Leiden: Brill. https://doi.org/10.1163/9789004256057 so this definition is actually misleading.

References

{{Alveolata Organelles Conoidasida