Raphidophyte

The raphidophytes, formally known as Raphidophycidae or Raphidophyceae (formerly referred to as Chloromonadophyceae and Chloromonadineae), are a small group of eukaryotic algae that includes both marine and freshwater species. All raphidophytes are unicellular, with large cells (50 to 100 μm), but no cell walls. Raphidophytes possess a pair of flagella, organised such that both originate from the same invagination (or gullet). One flagellum points forwards, and is covered in hair-like mastigonemes, while the other points backwards across the cell surface, lying within a ventral groove. Raphidophytes contain numerous ellipsoid chloroplasts, which contain chlorophylls a, c1 and c2. They also make use of accessory pigments including β-carotene and diadinoxanthin. Unlike other heterokontophytes, raphidophytes do not possess the photoreceptive organelle (or eyespot) typical of this group.

In terms of ecology, raphidophytes occur as photosynthetic autotrophs across a range of aquatic systems. Freshwater species are more common in acidic waters, such as pools in bogs. Marine species often produce large blooms in summer, particularly in coastal waters. Off the Japanese coast, the resulting red tides often cause disruption to fish farms, although raphidophytes are not usually responsible for toxic blooms.

The position of this group varied in former classifications. Some protozoologists treated the chloromonads as an order within the phytoflagellates. Some phycologists classified them with the Xanthophyceae and the Eustigmatophyceae in the division Xanthophyta. Others considered them as related to the Chrysophyceae, Dinophyceae, or Cryptophyceae Currently, raphidophytes are regarded as an independent lineage of algae within the class Raphidomonadea, which also includes the heliozoan group Actinophryida.

Taxonomy
The classification based on Cavalier-Smith and Scoble 2013 recognizes only one order, Chattonellales.
 * Subclass Raphidophycidae Cavalier-Smith 2013 [Raphidophyceae Chadefaud 1950 emend. Silva 1980 s.s. ; Chloromonadophyceae Rothmaler 1951 ; Raphidophyta]
 * Order Chattonellales Throndsen in Tomas, 1993 emend. Yamaguchi, Nakayama, Murakami & Inouye, 2010 [Vacuolariales ; Raphidomonadida Heywood & Leedale 1983 ; Chloromonadina Klebs 1892 ]
 * Genus Viridilobus Demir-Hilton et al. 2012
 * Family Fibrocapsaceae Cavalier-Smith 2013
 * Genus Fibrocapsa Toriumi & Takano 1973
 * Family Haramonadaceae Cavalier-Smith 2013
 * Genus Haramonas Horiguchi 1996
 * Family Vacuolariaceae [Chattonellaceae ; Gonyostomaceae ]
 * Genus Oltmannsia Schiller 1925
 * Genus Chlorinimonas Yamaguchi et al. 2010
 * Genus Heterosigma Hada 1967 ex Hara & Chihara 1987
 * Genus Chattonella Biecheler 1936 [Hornellia Subrahmanyan 1954 ; Hemieutreptia Hada 1974 ]
 * Family Vacuolariaceae
 * Genus Swirenkoiamonas Skvortzov 1968
 * Genus Vacuolaria Cienkowski 1870
 * Genus Merotricha Mereschkowsky 1877
 * Genus Gonyostomum Diesing 1866