Showing posts from April, 2016

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. euglypta2.

Cocconeis placentula / C. lineata from a 2003 Everglades sample (D…