Mediolabrus comicus

Mediolabrus comicus was originally described as Minidiscus comicus, but in 2020, it was transferred based on molecular phylogenetics to a newly erected genus Mediolabrus, as its type species.{{cite journal |last1=Li |first1=Yang |last2=Guo |first2=Xiao-Hui |last3=Lundholm |first3=Nina |title=Molecular Phylogeny and Taxonomy of the Genus Minidiscus (Bacillariophyceae), with Description of Mediolabrus gen. nov |journal=Journal of Phycology |date=December 2020 |volume=56 |issue=6 |pages=1443–1456 |doi=10.1111/jpy.13038 |pmid=32510583 |bibcode=2020JPcgy..56.1443L }}

File:Structure of diatom frustules.png]]

Cells of M. comicus have diameters between 1.9 and 6.0 μm. The larger cells are discoidal with flat valve faces (ends of the siliceous shell{{Cite web |title=Valve {{!}} Glossary - Diatoms of North America |url=https://diatoms.org/glossary/valve |access-date=2025-04-27 |website=diatoms.org |language=en-US}}), while the smaller ones are spherical or even oblong. Valve margins are very narrow and marginal areolae (small regularly repeated pores{{Cite web |title=Areola {{!}} Glossary - Diatoms of North America |url=https://diatoms.org/glossary/areola |access-date=2025-04-27 |website=diatoms.org |language=en-US}}) terminate close to the valve edge. There are 6–8 areolae per 1 μm. Each valve face has one central rimoportula (lip-like pore{{Cite web |title=Rimoportula {{!}} Glossary - Diatoms of North America |url=https://diatoms.org/glossary/rimoportula |access-date=2025-04-27 |website=diatoms.org |language=en-US}}) surrounded by two to four fultoportulae (tube-like pores{{Cite web |title=Fultoportula {{!}} Glossary - Diatoms of North America |url=https://diatoms.org/glossary/fultoportula |access-date=2025-04-27 |website=diatoms.org |language=en-US}}). Only a single rimoportula near the valve center is a diagnostic feature of the genus Mediolabrus. External fultoportula tubes are well developed as fluted cylinders, rising to over 0.5 μm in height above the mantle (side of the valve{{Cite web |title=Mantle {{!}} Glossary - Diatoms of North America |url=https://diatoms.org/glossary/mantle |access-date=2025-04-27 |website=diatoms.org |language=en-US}}). The central rimoportula tube can reach up to 2.4 μm in height in large cells. The copulae that protect dividing cells{{Cite web |title=Copula {{!}} Glossary - Diatoms of North America |url=https://diatoms.org/glossary/copula |access-date=2025-04-27 |website=diatoms.org |language=en-US}} are very thin and not discernible in non-dividing cells. The fultoportulae extrude long threads (presumably of chitin) that connect cells within the small colonies.

M. comicus, like other diatoms, undergoes a multi-year life cycle during which its cells get increasingly smaller in diameter with each asexual division, until they reach a point of size restoration, presumably connected to a sexual process. David Jewson and colleagues studied samples of M. comicus collected in the western Mediterranean by RV Sarmiento de Gamboa between March and September 2009. This allowed them to explore the diversity of shapes and sizes of cells during different phases of algal bloom development, as well as the life cycle of the algae.

They found a strong relationship between cell diameter and shape. The largest cells, with diameters above 4 μm, are cylindrical with flat or slightly domed valves. As the cell diameter declines with each consecutive division, doming of the valve faces becomes more pronounced, until they become spherical at around 3 μm (this is also the size at which size restoration starts occurring) and some cells even become oblong at around 2 μm. This allows M. comicus to keep its cell volume relatiovely stable, even though the diameter changes dramatically.

Mediolabrus comicus was first described from a red tide in Tokyo harbour on September 17, 1980, forming large aggregated flocks.{{cite journal |last1=Takano |first1=Hideaki |date=1981 |title=New and Rare Diatoms from Japanese Marine Waters-VI. Three New Species in Thalassiosiraceae |journal=東海区水産研究所研究報告 |trans-journal=Bulletin of Tokai Regional Fisheries Research Laboratory |volume=105 |issue=10 |pages=31–43 |url=https://agriknowledge.affrc.go.jp/RN/2010243988.pdf |id={{NAID|40002575148}} }} Since then it has usually been found as solitary cells or forming short chains of 2 or 3 cells.{{cite journal |last1=Kaczmarska |first1=Irena |last2=Lovejoy |first2=Connie |last3=Potvin |first3=Marianne |last4=Macgillivary |first4=Michael |title=Morphological and molecular characteristics of selected species of Minidiscus (Bacillariophyta, Thalassiosiraceae) |journal=European Journal of Phycology |date=November 2009 |volume=44 |issue=4 |pages=461–475 |doi=10.1080/09670260902855873 |bibcode=2009EJPhy..44..461K }} It is widespread along the Pacific and Atlantic coasts and in the Adriatic and Mediterranean seas,{{Cite journal |last=Lange |first=Kb |date=1985-01-01 |title=Spatial and seasonal-variations of diatom assemblages off the argentinian coast (south western atlantic) |url=https://archimer.ifremer.fr/doc/00112/22324/ |journal=Oceanologica Acta |language=en |volume=8 |issue=3 |pages=361–369 }}{{cite book |last1=Bérard-Therriault |first1=Lyse |last2=Poulin |first2=Michel |last3=Bossé |first3=Luci |title=Guide d'identification du phytoplancton marin de l'estuaire et du golfe du Saint-Laurent: incluant également certains protozoaires |trans-title=Identification guide to marine phytoplankton of the Estuary and Gulf of St. Lawrence: also including certain protozoa |language=fr |date=1999 |publisher=NRC Research Press |isbn=978-0-660-96057-9 }}{{pn|date=April 2025}}{{cite journal |last1=Percopo |first1=Isabella |last2=Siano |first2=Raffaele |last3=Cerino |first3=Federica |last4=Sarno |first4=Diana |last5=Zingone |first5=Adriana |title=Phytoplankton diversity during the spring bloom in the northwestern Mediterranean Sea |journal=Botanica Marina |date=2011 |volume=54 |issue=3 |page=33 |doi=10.1515/bot.2011.033 |bibcode=2011BoMar..54...33P |url=https://archimer.ifremer.fr/doc/00038/14916/12245.pdf }}{{cite journal |last1=Lee |first1=Sang Deuk |last2=Park |first2=Joon Sang |last3=Lee |first3=Jin Hwan |title=New Record of Diatom Species in Korean Coastal Waters |journal=Korean Journal of Environmental Biology |date=2012 |volume=30 |issue=3 |pages=245–271 |url=https://www.ebr.or.kr/journal/article.php?code=14448 }}{{cite journal |last1=Grižančić |first1=Lana |last2=Baričević |first2=Ana |last3=Smodlaka Tanković |first3=Mirta |last4=Vlašiček |first4=Ivan |last5=Knjaz |first5=Mia |last6=Podolšak |first6=Ivan |last7=Kogovšek |first7=Tjaša |last8=Pfannkuchen |first8=Martin |last9=Marić Pfannkuchen |first9=Daniela |title=A metabarcode based (species) inventory of the northern Adriatic phytoplankton |journal=Biodiversity Data Journal |date=25 September 2023 |volume=11 |pages=e106947 |doi=10.3897/BDJ.11.e106947 |doi-access=free |pmid=38318520 |pmc=10840511 }} suggesting a cosmopolitan distribution.

In 2013, scientists aboard the research vessel Téthys II studied a large annual spring phytoplankton bloom in the Gulf of Lions (northwestern Mediterranean Sea) and found that contrary to expectations, it was dominated by two species of nanophytoplanktonic diatoms: M. comicus and Minidiscus trioculatus. Such intense blooms were thought to be caused by larger chain-forming diatom genera and the tiny Minidiscus and Mediolabrus have never been documented as their dominant constituents in the Mediterranean before. The same study also found out that these smallest diatoms can reach the seafloor at high sinking rates, potentially contributing to carbon export much more substantially than previously expected.{{Cite web |date=2012-08-31 |title=DeWEX (Impacts of deep water formation on mediterranean pelagic ecosystems) - MERMEX {{!}} CNRS Terre & Univers |url=https://www.insu.cnrs.fr/fr/cnrsinfo/dewex-impacts-deep-water-formation-mediterranean-pelagic-ecosystems-mermex |access-date=2025-04-27 |website=www.insu.cnrs.fr |language=fr}}

• Smallest organisms

{{Reflist}}

• {{AlgaeBase species|name=Mediolabrus comicus|id=178541}}
• [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2590921 Mediolabrus comicus in NCBI Taxonomy]
• [https://www.diatombase.org/aphia.php?p=sourcedetails&id=477338 Mediolabrus comicus in DiatomBase]
• [https://www.obis.org/taxon/1728736 Mediolabrus comicus in OBIS]

{{Taxonbar|from=Q134168694}}

Category:Thalassiosirales

Category:Diatom species

Category:Protists described in 1981