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Name derivation:

Gr. actin - ray or beam; Gr. sphaer - sphere

Classification:

Actinosphaerium Ritter von Stein 1857

Order Actinophryida; Family Actinosphaeriidae (Guiry and Guiry 2017)

Also placed in Heliozoa or Stramenopiles or Mycetozoa or Sarcomastiqophora, Heliozoa (Encyclopedia of life)

Morphology:

Spherical unicells 200 – 1000 μm diameter with spiny pseudopodial projections called ‘axopods’radiating in all directions and up to 100 μm long.  Cells have contractile vacuoles near periphery for buoyancy adjustment.  Pseudopods contain coiled microtubules for support, and are sticky so they adhere to prey.

Heterotrophic (no chlorophyll).  Prey include flagellates, ciliates other algae, and presumably bacteria.

Similar genera:

 

Habitat:

Relatively common in freshwater lakes and streams.  Can also be found in damp terrestrial microhabitats such as attached to damp moss.  Found in Christine Lake (Jackson NH USA) by Oliver Bender (September 2017).

Toxicity:

Non-toxic.

 

References:

Guiry, M.D. and G.M. Guiry  2013.  AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.  http://www.algaebase.org; searched on 10 September 2013.