Chroomonas | Komma

Introduction

• Chroomonas described by Hansgirg; type species Chroomonas nordstedtii (freshwater, Hansgirg 1885)
• Komma described by Hill; type species Komma caudata (Hill 1991b)

Characteristics

• Type of biliprotein: PC630 or PC645
• Dimorphism unknown
• Light microscopy: blue-green to blue cells, freshwater and/or marine, one plastid with a pyrenoid, gullet with small opening (usually hardly visible), sometimes with an eyespot close to the pyrenoid
• Ultrastructure: staggered rectangular periplast plates, gullet may be forked, thylakoids traverse the pyrenoid matrix, nucleomorph free in periplastidial space (Santore 1984)
• Komma differs from Chroomonas in cell shape (pointed comma-shaped cells) and periplast (SPC and IPC made of hexagonal plates)
  

Discussion of Phylogenetic Relationships

Blue-green cryptophytes with hexagonal periplast plates and with a pointed antapex bent towards the ventral side have been separated from Chroomonas (staggered rectangular plates) as the genus Komma. Some Chroomonas species are considered of uncertain status because they contain phycocyanin 630 (absorption maxima at 630 and 583 nm).

In molecular phylogenies, the genus Chroomonas is split up in two clades with Hemiselmis evolving from between the two (Figure 1). The sister clade to Hemiselmis is further subdivided into three clades. By genetic divergence each of the four Chroomonas clades may be considered a separate genus (Hoef-Emden 2008). An examination of the type material of Chroomonas nordstedtii Hansgirg by scanning electron microscopy showed that the current definition of the genus Chroomonas may be wrong. The type material contained elliptical cells with hexagonal periplast plates (Novarino 2003).

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Figure 1. Molecular phylogeny of the genera Chroomonas, Hemiselmis and Komma. Maximum likelihood tree inferred from nucleomorph SSU rDNA sequences. PC, phycocyanin; PE, phycoerythrin; scale bar = substitutions per site. © 2008 Kerstin Hoef-Emden

References

Hansgirg A (1885) Anhang zu meiner Abhandlung „Ueber den Polymorphismus der Algen“. Bot. Zentralbl. 23: 229-233

Hill DRA (1991b) Chroomonas and other blue-green cryptomonads. J. Phycol. 27: 133-145

Santore UJ (1984) Some aspects of taxonomy in the Cryptophyceae. New Phytol. 98: 627-646

Hoef-Emden K (2008) Molecular phylogeny of phycocyanin-containing cryptophytes: Evolution of biliproteins and geographical distribution. J. Phycol. 44: 985-993

Novarino G (2003) A companion to the identification of cryptomonad flagellates (Cryptophyceae = Cryptomonadea). Hydrobiologia 502: 225-270