in vivo, lateral view

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Portrait (lateral view) of the cinetochilid scuticociliate, Sphenostomella vernalis (Dragesco and Groliere, 1969) Jankowski, 1980 (synonym: Sathrophilus vernalis). The cell is elongate ovoid. The many large mucocysts give the cell a yellowish-orange color when viewed by brightfield illumination. The roughly triangular peristome is in the anterior 1/3 (not visible in this view). There are 31-34 longitudinal somatic kineties. There are two left postoral kineties and one right postoral kinety (K1). There is a cluster of unciliated kinetids (scutica) adjacent to the posterior margin of the peristome. There is a short preoral suture and a longer broader postoral suture. There is a long caudal cilium. Groliere states that a long caudal cilium was absent in his population of S. vernalis (Groliere, C-A., J. Protozool. 20 (3): 369-376, 1973). Since all individuals collected from several different sites near Boise, Idaho had a long caudal cilium (visible here)and otherwise were indistinguishable from the description by Groliere I have designated this species as S. vernalis.The genus Sphenostomella is monotypic to date. The cleft-like cytoproct is located in the ventral midline in the posterior suture between the excretory pore of the contractile vacuole and the posterior margin of the peristome. There are prominent transverse fibrils between the 2nd and 3rd right somatic kineties as they diverge anteriorly. These are stained in silver nitrate preparations. There is a semicircular undulating membrane on the right margin of the peristome. There are three adoral membranelles. The M1 is an obliquely oriented group of 3 kineties. Its hook-shaped anterior end nearly reaches the anterior end of the undulating membrane. The M2 lies parallel to and is longer than M1 and also has a hook-shaped group of kinetids at its anterior end. M3 has broad “U” shape directed anteriorly. Fibrils radiate from the posterior margin of the peristome toward the cytostome. There is a single central spherical macronucleus and an adjacent micronucleus. Collected from polysaprobic standing ditchwater at several different sites near Boise, Idaho March 2005. DIC.