Rhodomonas

Discovery Rhodomonas was first described by G. Karsten in 1898 as a “strange, swimming organism”. The first indication of Rhodomonas’ existence was Karsten's observation of its proliferation in a sample containing diatoms, seashells, stones, and the brown algae Sphacelaria. Consequently, this raises doubt as to whether an organism that is placed in Rhodomonas truly belongs in that genus. With this perspective, there is support to transfer members of Rhodomonas to the synonymous genus Pyrenomonas. Notably, in recent phylogenies based on molecular data, the genera Rhodomonas, Rhinomonas, and Storeatula are all grouped together based on shared similarity of the examined genetic sequences. Given how closely related these genera are, there is some uncertainty as to how distinct the genus Rhodomonas is from Rhinomonas and Storeatula. Dimorphism has been reported in cryptomonads and is hypothesized to apply to many genera, such that some currently existing genera may actually be different morphs of one group. Applying this to the context of Rhodomonas, the genus Storeatula has been suggested to be a possible alternating morphotype for Rhinomonas and Rhodomonas due to mixing of the three groups in molecular phylogenies. Further investigation is needed to better support these findings. == Habitat and ecology ==

Rhodomonas resides in marine environments across the globe, with some reports of freshwater species. Like many other cryptomonads, Rhodomonas species are photosynthetic. It is currently unknown if they are capable of heterotrophy. == Morphology ==

The size of Rhodomonas species has been reported as ranging from 9-40 𝜇m, with variability between researcher reports. Within the cell, the chloroplast is found within the plastidial compartment and has close structural association with the pyrenoid. The chloroplast has two lobes and is shaped like the letter H. The pyrenoid sits between the two lobes of the chloroplast, surrounded by starch. The thylakoids of the chloroplast are unable to penetrate through the pyrenoidal matrix, and consequently do not cross through the pyrenoid. Rhodomonas usually contains one chloroplast, although rare reports with the observation of two chloroplasts exist. The vestibulum-furrow-gullet system is a defining characteristic of Rhodomonas. The vestibulum is located below the anterior apex of the cell, from which two flagella extend as is characteristic of cryptomonads. The vestibulum transforms posteriorly into a furrow that closes into a gullet. The gullet is short and tubular, while the furrow can vary in length depending on the species. The gullet is lined with ejectisomes that eject substances outside of the cell. The nucleomorph of Rhodomonas sits in an indentation of the periplastidial cytoplasm into the pyrenoid. This has also been termed as the pyrenoidal bridge. This trait is shared with Rhinomonas and Storeatula, other genera that are often grouped with Rhodomonas . Rhodomonas also contains a single nucleus, located posteriorly within the cell. In the opposite direction, a contractile vacuole is located near the anterior apex of the cell. Like many other cryptomonads, Rhodomonas reproduces through asexual division. It is not currently known if they are capable of sexual reproduction. == Aquaculture ==

Rhodomonas species have been identified as a beneficial feed in aquaculture. Among other organisms, they are ideal for feeding copepods, brine shrimps, and scallop larvae. Their benefits as live feed for aquaculture can be attributed to their high fatty acid and protein content, which increases their nutritional content. It has been observed that under nitrogen starvation conditions, their nutritional content can increase. == Species ==

The genus Rhodomonas includes the following species: • Rhodomonas abbreviata Butcher 1967 ex Hill & Wetherbee 1989 • Rhodomonas atrorosea Butcher ex Hill & Wetherbee 1989 • Rhodomonas radix Javornický 2001 • Rhodomonas stigmatica (Wislouch 1924) Hill 1991 • Rhodomonas tenuis Skuja 1948 ==References==