Ploesoma triacanthum (Bergendal, 1892)

Most likely ID: n.a.


Synonym: Ploesoma lynceus


Sampling location: Simmelried


Phylogenetic tree: Ploesoma triacanthum



  • body bag-shaped
  • length 136–220 µm
  • lorica of one piece, surface granulated with longitudinal ridges
  • lorica ventrally open
  • lorica with three anterior spines, the middle one curved downwards
  • corona with a pair of frontal palps
  • foot mid-ventral
  • foot annulated with long pointed toes
  • one eyespot
Ploesoma triacanthum

So far I have found Ploesoma triacanthum exclusively in Simmelried between floating plant masses. I have had no evidence also of a planktonic lifestyle from my other sites. The findings are limited to May 2004, July, 2005 and August 2005. Before and after I could not detect the species. With the foot on the ventral side and the 3 apical spines Ploesoma triacanthum is comparatively easy to identify and to distinguish from the other Ploesoma species.


More images and information of Ploesoma triacanthum: Michael Plewka-Freshwater life-Ploesoma triacanthum


Fig. 1 a-b: Ploesoma triacanthum. L = 190 µm. Lateral view of a slightly squashed specimen from right. One of the apical spines is visible (arrow). Obj. 40 X.


Fig. 2: Ploesoma triacanthum. L = 190 µm. Focus on one of the two apical palps (PA). Obj. 40 X.


Fig. 3: Ploesoma triacanthum. Detail of the lateral structure of the lorica. Three longitudinal ridges run along the lateral midline. Apically two of the three tooth-sphaped spines (TS) on the dorsal side are visible. D = dorsal side, V = ventral side. Obj. 100 X.


Fig. 4 a-b: Ploesoma triacanthum. L = 194 (with foot). A freely swimming specimen subventrally (a) and from the left. Note the ventral slit (VS). FT = foot, TO = toes. Obj. 40 X.