Achnanthidium is a mainly freshwater genus, often found in high energy waters, such as streams and rivers, or the upper layers of lakes. This may indicate a preference for high oxygen levels, or it may be that nutrients are more easily obtained in such high energy environments.
Achnanthidium is a single raphe (monoraphid) genus, also known as heterovalvar - posessing two valves which differ. Usually solitary, but individuals may collect in small numbers to form chains. They attach to the substrate, either stones or plants, by mucilage stalks. The girdle view illustrates the shallow V shape characteristic of this genus. The valve with the raphe is the concave, inner valve, the outer convex valve being rapheless. The mucilage stalk arises from the inner, concave, raphe valve.
Achnanthidium (species unidentified).
Found in diatomite deposit at Three Lakes, core TL5, at 3.6 to 3.7 m depth.
See Achnanthidium on Algaebase or Diatoms.org or Natural History Museum of Wales