Morphology and infraciliature of a marine scuticociliate with a polymorphic life cycle: Urocryptum tortum n. gen., n. comb.

A new genus and species combination are proposed for Urocryptum tortum n. g en.. n. comb., a scuticociliate with a polymorphic life cycle. This marine ciliate was isolated from a sample taken at Gokasho Bay in Mie Prefecture ( Japan). Specimens from different phases of the growth cycle were examined i n vivo and with two silver staining techniques. Three life-history stages w ere observed: an exponential growth phase stage (trophont), a stationary ph ase stage (tomite). and finally a resting stage (cyst). The exponential gro wth form is laterally flattened and ovoid: it has 20-24 somatic kineties (S K) and a typical complement of scuticociliate oral structures. Polykinetid 1 (Pk1) has two longitudinal files of 6 kinetosomes (Ks); sometimes one or two additional kinetosomes are located anteriorly. Polykinetid 2 (Pk2) has two files of 6 or 7 Ks: a third file of three widely spaced kinetosomes is located on its right side, as well as a small curved row of 5 Ks positioned on the right hand side of the posterior end of Pk2. Polykinetid 3 (Pk3) ha s 3 rows of 4. 5. and 7 Ks's perpendicular to the haplokinety (Hk) or paror al membrane. The stationary growth phase cell is spindle-shaped and has a s imilar number of SK that are much more closely spaced than in exponentially growing specimens. Oral infraciliary structures are reduced in size, havin g fewer kinetosomes and bring positioned more anteriorly in the cell. Pk1 i s composed of two files of 5-6 Ks. Pk2 has only two tiles of 6-7 Ks, and Pk 3 has two to three rows of 3-4 Ks. The Hk is displaced anteriorly and becom es straight, losing the shape typical of exponential growth phase cells. Cy sts are pyriform with a wide cyst wall: no infraciliary structures were vis ible.