Redescription of Strombidium coronatum (Leegaard, 1915) Kahl, 1932 (Ciliophora, Spirotricha) based on live observation, protargol impregnation, and scanning electron microscopy

The oligotrichid ciliate Strombidium coronatum (Leegaard, 1915) Kahl, 1932 is redescribed from plankton samples taken in the Irish Sea, using live observation, protargol impregnation, and scanning electron microscopy. The species is characterized by a conspicuous, uniquelly shaped peristome, which is flat and roughly triangular and extends in the sagittal plane. The Irish Sea specimens measure ~ 45 × 25 µm in vivo and ~ 40 × 24 µm after protargol impregnation. The girdle kinety is equatorial, ostensibly continuous, and composed of ~ 100 dikinetids. The ventral kinety extends longitudinally on the posterior fifth of the cell and is composed of about five dikinetids. The adoral zone of membranelles is widely open and composed of ~ 18 collar and ~ 12 buccal membranelles; the collar portion is disconnected from the buccal portion. The shape and orientation of the opisthe’s adoral zone of membranelles are apparently extraordinary, i.e., the membranelles form an inverted L-shaped stripe extending longitudinally in the elongated posterior cell portion of dividers.