Trachelomonas – Kinneret Algae Atlas

Phylum: Euglenophyta
Class: Euglenophyceae
Order: Euglenales
Habitat: plankton, pelagic
Distinctive features: Near-spherical flagellated cells encapsulated in a brown with a distinctive “mouth” opening through which the locomotive emerges.
Organization: single flagellated cells
Color: brown
Cell shape: sphaeroid
Cell diameter (D): 8.9-15.5 μm (median=11.4 μm). Range reported is 5^th-95^th percentiles for 234 cells measured during 2004-2009.
Cell biovolume: 370 - 2000 μm³, median: 800 μm³.
Biovolume equation: sphere, V, μm³ = ¾ π (D/2)³

Morphological features

Trachelomonas cells are similar to those of Euglena, except that they are completely encased in a mucilaginous rigid envelope outside the plasma membrane called lorica (Plates 1, 2). This lorica is highly mineralized and dark brown in color. The cell is flagellated and capable of euglenoid movement within the lorica as well as swimming out of it (Plate 2). The lorica has a bottle-neck-shaped opening through which the flagellum emerges and through which the cell may swim out for cell division or when conditions require, then may swim back into it. Trachelomonas is distinguishable from other spherical unicellular species occurring in Lake Kinneret by the bottle-neck-shaped opening of its lorica, at the top part of the cell (arrow in Plate 1). This structure can be seen only when the cell is observed from the side, not when it is observed from above or below.

Plate 1. Typical Trachelomonas: a euglenoid cell encapsulated by a thick lorica. Left: bright field; Many chlorophytes arranged around cell periphery, large circular nucleus in it center. Arrow indicates the protruding opening of the lorica from which the flagellum extends (but is not seen here). Right: dark field. Photos by Tamar Zohary.

Plate 2. Trachelomonas hispida (Perty) Stein 1878 from Lake Kinneret. The Euglena-like cell is exiting its brown-colored lorica. The single flagellum is seen extending though an opening in the lorica at its bottom end. Photos by Alla Alster.

Ecology

Trachelomonas is the only euglenoid seen in Kinneret pelagic plankton samples quite often, although this genus too is never abundant, maximum cell density ever recorded was ~50/mL (Fig. 1). Trachelomonas can be viewed at any time of the year but tends to appear more often in spring (March-April) and rarely from August to October. (Fig. 2). Cell size varies only slightly, with no distinct annual pattern (Fig. 2).

Environmental conditions

The abundance of Trachelomonas spp. in the pelagic water of Lake Kinneret was indifferent to water temperature, ambient chloride concentration (Fig. 3), water level, pH, Ca, , Si, NO₃, NH₄ and Z_mix/Z_eu ratio (not shown). Higher abundances of the genus were recorded when depth-integrated (0-15 m) chlorophyll concentrations were < 500 mg m^-2, and organic N > 0.15 mg N L^-1 (Fig. 3).

Additional figures

Figure 1. Time series of Trachelomonas spp. abundance (cells mL^-1), Lake Kinneret, 1999-2020.

Figure 2. The annual pattern of water column cell abundance (left) and volume per cell (right) of Trachelomonas spp., based on data for 1999-2014. Statistics shown: median – middle line; 25th to 75th percentiles – box content; 90th and 10th percentiles – top and bottom bars, respectively.

Figure 3. Trachelomonas spp. abundance (cells mL^-1) vs. environmental parameters recorded at the site and time of sampling, showing indifference to water temperature (avg. 0-10 m) and ambient chloride concentration, higher abundance at lower chlorophyll (no major bloom of another species), and higher Organic N.

Cite this record as: Dr. Tamar Zohary, Dr. Alla Alster. 16 June 2026. Electronic publication. Israel Oceanographic & Limnological Research. https://kinneret-algae-atlas.org/ Searched on —.