Diatom of the month – April 2016: Cocconeis placentula
by Luca Marazzi* ‘Who’ is it and where does it live? This diatom is monoraphid, that is to say it has a raphe only on one valve, as shown in the figures. Monoraphid species are one of 9 major morphological types of diatoms - the other ones are: centric (like Cyclotella meneghiniana ) , araphid (e.g. Asterionella formosa , which forms star-shaped colonies !), eunotioid (e.g. the beautifully ornamented Eunotia diadema ), symmetrical biraphid (e.g. the slender Navicula lanceolata ), asymmetrical biraphid (e.g. Gomphonema parvulum ), epithemioid (e.g. Rhopalodia gibba , which hosts nitrogen-fixing bacteria as symbionts), nitzschioid (e.g. the organic pollution-loving Nitzschia palea ), and surirelloid (the big Surirella ovalis ) 1 . Like in many other cases, the taxonomy is far from settled though; following recent research, numerous specimens usually named C. placentula should be more accurately named Cocconeis lineata and C. euglypta 2 . ...