Redescription of Strombidinopsis minima (Gruber, 1884) Lynn et al., 1991 (Protozoa, Ciliophora), with notes on its ontogenesis and distribution

Strombidinopsis minima (Gruber, 1884) Lynn et al., 1991 has a ciliary pattern typical for strombidinopsids but is characterized by a "mineral envelope" posterior to the zone of external membranelles. The mineral envelope consists of silt particles embedded in a mucous matrix to which organic debris may adhere. It is regarded as an adaptation to life in turbid waters, which developed convergently in several groups, e.g. peritrichs, karyorelictids, plagiopylids, hymenostomatids, cyrtophorids, and colpodids. The morphology and the ciliary pattern of specimens collected at the shore of a salt lagoon near Venice (Italy) and a salt pan in Venezuela were investigated using live observation and protargol impregnation. For the first time, a Strombidinopsis species was also studied by scanning electron microscopy. Strombidinopsis minima is probably a euryhaline cosmopolitan species, preferring coastal and inland waters. Its cell division is enantiotropic with a hypoapokinetal development of the oral primordium above two anteriorly shortened dorsal kineties, while the primordium forms between two dorsal kineties of ordinary length in S. spinifera and S. acuminata. Since the genus Strombidinopsis lacked a type species, the well-known S. acuminata was so designated.