Strombidinopsis

Strombidinopsis Kent, 1881 (ref. ID; 2014, 4917) or 1882 (ref. ID; 3388)

Class Polyhymenophora: Subclass Spirotricha: Order Oligotrichida: Suborder Oligotrichina (ref. ID; 2014)
Order Choreotrichida Small & Lynn, 1985: Family Strombidinopsidae Small & Lynn, 1985 (ref. ID; 4917)

[ref. ID; 2014]
The body may be approximately cylindrical in shape with the posterior region broadly rounded and the apical end truncate or the shape may be an elongate pyriform. Somatic cilia distributed over the entire body surface and arranged in many (20 or more) longitudinal kineties. The apical conspicuous AZM is of the closed type and is situated on the rim of a ledge encircling the depressed apical peristome region. Somatic cilia short and not very mobile. There is some confusion in the literature concerning the generic name of certain species and the authors recommend the accounts by Faure-Fremiet and particularly that published in 1969 rather than the keys of Kahl which are confused and out of date.
Quote; Colin R. Curds, Michael A. Gates and David McL. Roberts "British and other freshwater ciliated protozoa Part II Ciliophora: Oligohymenophora and Polyhymenophora" Cambridge University Press, 1983 (ref. ID; 2014)

[ref. ID; 3389]
Body (50-80 um) oval, elongated or conical. The peristomial field is large. The circlet of adoral membranelles which are confined at the apical area is closed. Fine and short cilia cover almost the entire body. Cilial rows are formed in one species. The body is covered with an inconspicuous mucus envelope in some stages of the animal. Found in freshwater. (ref. ID; 3389)

[ref. ID; 7441]
Systematics and phylogeny; Faure-Fremiet (1969) used the "closed circle" of OPk's to separate the tintinnines, strobilidiids, and the strombidinopsids from the strombidiids and halteriids, which have an "open circle". Small and Lynn (1985) followed this approach, dividing their Subclass Choreotrichia into the Order Oligotrichida, including the families Halteriidae and Strombidiidae, and Order Choreotrichida, including the Suborders Tintinnina, Strobilidiina, and Strombidinopsina. Petz and Foissner (1992) used three features of division morphogenesis to infer the phylogenetic relationship between these groups. Their phylogenetic analysis using Hennigian techniques suggested that halteriids were a sister taxon, their Subclass Halteriia, to a clade, their Subclass Oligotichia, which included the Strombidiidae and tintinnines and strobilidiines. Laval-Peuto et l. (1994), essentially following Faure-Fremiet (1969) and Small and Lynn (1985), have elevated the oligotrichs to a class with two included subclasses: the Subclass Oligotrichia with an "open circle", including the Order Oligotrichida with suborders Halteriina and Strombidiina; and the Subclass Strobilia, including the Order Choreotrichida and Order Tintinnida. Their Order Choreotrichida includes strombidinopsids, strobilidiids, Lohmanniella, and Leegaardiella. There is only one synapomorphy that unites Strombidium, Strobilidium, and the tintinnines (Petz and Foisser 1992): this is the movement of the anlage into a subsurface invagination of the cortex. However, this also occurs in euplotid-like hypotrichs (Deroux 1974), such as Euplotes (Ruffolo 1976; Wise 1965). Thus, as suggested by Petz and Foissner (1992), it could very easily be a convergent character even within the oligotrichs. What is much more striking in out view is the strong similarity in the rotation of the opisthe's oral primordium and opisthe's somatic kineties in halteriids and Strombidium, ultimately resulting in the classical enantiotropic cell division. On the other hand, Strobilidium, tintinnines, and Strombidinopsis rotate the oral apparatus within the subsurface pouch, do not rotate the opisthe's somatic kineties 180 degrees, and divide in a quite modified kind of enantiotropic cell division. Emphasis on these features would support the system of Small and Lynn (1985). (ref. ID; 7441)

Strombidinopsis acuminatum Faure-Fremiet, 1924 (ref. ID; 4917) reported author and year? (ref. ID; 7441)
See; Strobilidium acuminatum (ref. ID; 3389)
Strombidinopsis armeniensis Zharikov, 1987 (ref. ID; 4917)
Strombidinopsis azerbaijanica Alekperov and Asadullayeva, 1997 (ref. ID; 4917)
Strombidinopsis batos Lynn et al., 1991 (ref. ID; 4917)
Strombidinopsis cheshiri Snyder & Ohman, 1991 (ref. ID; 7330, 7441)
Strombidinopsis chilorhax Lynn et al., 1991 (ref. ID; 4917)
Strombidinopsis claparedei Faure-Fremiet, 1924
See; Strombidinopsis gyrans (ref. ID; 1621), Strobilidium claparedei (ref. ID; 3389)
Strombidinopsis elegans Song & Bradbury, 1998 (ref. ID; 4917)
Strombidinopsis gyrans Kent, 1881 (ref. ID; 1621, 4917) or 1882 (ref. ID; 3388, 3389) reported year? (ref. ID; 1618)
Syn; Strombidinopsis claparedei Faure-Fremiet, 1924 (ref. ID; 1621); Strombidinopsis paradoxus Smith, 1899 (ref. ID; 3389); Strombidium turbo Claparede & Lachmann-Roux (ref. ID; 1621); Tintinnidium ranunculi Penard, 1912-Kent, 1926 (ref. ID; 1621) or Penard, 1922 (ref. ID; 3389); Tintinnidium semiciliatum (Sterki, 1879) Kent, 1881 (ref. ID; 4917)
Strombidinopsis jeokjo Jeong et al., 2004 (ref. ID; 4992)
Strombidinopsis minima (Gruber, 1884) Lynn, Montagnes, Dale, Gilron & Strom, 1991 (ref. ID; 4917 redescribed paper)
Syn; Strombidium minima Gruber, 1884 (ref. ID; 4917)
Strombidinopsis multiauris Montagnes & Taylor, 1994 (ref. ID; 7330 original paper)
Strombidinopsis paradoxus Smith, 1899
See; Strombidinopsis gyrans (ref. ID; 3389)
Strombidinopsis pelagicum Faure-Fremiet, 1924 (ref. ID; 4917)
Strombidinopsis proboscidifer Milne, 1886-7
See; Strobilidium proboscidiferum (ref. ID; 3389)
Strombidinopsis setigera Stokes, 1885 (ref. ID; 1621, 3389, 4917)
Syn; Strombidinopsis similis Stokes, 1891 (ref. ID; 1621); Tintinnidium setigerum (Stokes, 1885) Roux, 1901 (ref. ID; 3389)
Strombidinopsis similis Stokes, 1891
See; Strombidinopsis setigera (ref. ID; 1621, 3389)
Strombidinopsis sphaira Lynn et al., 1991 (ref. ID; 4917)
Strombidinopsis spiniferum Lynn et al., 1991 (ref. ID; 7441)
Strombidinopsis typicum (Lankester, 1874) Faure-Fremiet, 1924 (ref. ID; 4917)

Strombidinopsis acuminatum Faure-Fremiet, 1924 (ref. ID; 4917) reported author and year? (ref. ID; 7441)

See

Strobilidium acuminatum (ref. ID; 3389)

Description

See the description of S. spiniferum. (ref. ID; 7441)

Strombidinopsis cheshiri Snyder & Ohman, 1991 (ref. ID; 7330, 7441)

Descriptions

Cell round or cylindrical often with tapering posterior, 62 um (range, 35-82) long and 38 um (29-49) wide. External polykinetid (EPZ) zone and internal polykinetid zone (IPZ) not compleley separate, EPZ comprised of 15-16 external polykinetids (EPk) which surround the anterior end. Cilia of the EPk are short near the cell centre and increase in length with distance from the cell centre (minimum length 3-5 um, maximum length ~25 um). EPk also show subtle division into two ciliary zones: outer cilia 20-35 um long, inner cilia 3-10 um long; this separation occurs approximately half way along the polykinetid. Deep oral cavity acentrically placed within the circle of external polykinetids. IPZ comprised of 6-10 polykinetids that lie in oral cavity; 4-5 internal polykinetids are completely separate; the rest are extensions of external polykinetids. Somatic kineties, 14 (13-19), equally spaced around cell, composed of 20-40 dikinetids (both with 3-4 um cilia), extend from oral region to posterior pole. Macronuclei, typically 2 (range, 1-6) semi-spherical (10 um in diameter). (ref. ID; 7330)

Discussion of related species

Lynn et al. (1991) have rediagnosed the Strombidinopsidae as: free swimming aloriate ciliates with many (usually >10) ciliated somatic kineties, extending the entire length of the cell, composed of dikinetids. Species of this family also typically have two similarly-shaped spherical to ovoid macronuclei; the genus Strombidinopsis has characters of the family. Strain SPJSC possesses these characters and consequently has been placed in the genus Strombidinopsis. Although the ranges are not identical, all the observed characters of strain SPJSC (i.e. length, width, external and internal polykinetid number, somatic kinety number, kinetosomes per kinety, somatic cilia length, macronuclear size and number, general shape) overlap with those used to describe Strombidinopsis cheshiri Snyder and Ohman, 1991, isolated from Southern California waters. Hence, we consider strain SPJSC to be a northern isolate of S. cheshiri. (ref. ID; 7330)

Remarks

The ciliate typically swam in a straight line with a helical movement, somewhat analogous to that described for a species of Strombidium (Fenchel and Jonsson 1988), Fenchel and Jonsson (1988) however, attributed a portion this helical mortion to Strombidium's asymmetric positioning of oral polykinetids, but such an arrangement does not exist for Strombidinopsis; possibly another mechanism controls its swimming behaviour. (ref. ID; 7330)

Time and locality of isolation

June from 1 m depth, temperature of 20 degrees C, and salinity of 20 0/00 in Sechelt Inlet, British Columbia, Canada (123 degrees 45'W, 49 degrees 40'N). (ref. ID; 7330)

Deposition of type material

A slide, USNM #47750, of protargol-stained cells representing an hapantotype from strain 1509 resides in the Ciliate Type Specimen Collection, US Natural History Museum, Smithsonian Institution, Washigton, D.C. (ref. ID; 7330)

Strombidinopsis gyrans Kent, 1881 (ref. ID; 1621) or 1882 (ref. ID; 3388, 3389) reported year? (ref. ID; 1618)

Synonym

Strombidinopsis claparedei Faure-Fremiet, 1924 (ref. ID; 1621); Strombidinopsis paradoxus Smith, 1899 (ref. ID; 3389); Strombidium turbo Claparede & Lachmann-Roux (ref. ID; 1621); Tintinnidium ranunculi Penard, 1912-Kent, 1926 (ref. ID; 1621) or Penard, 1922 (ref. ID; 3389); Tintinnidium semiciliatum (Sterki, 1879) Kent, 1881 (ref. ID; 4917)

Descriptions

Fresh water pond. (ref. ID; 1618)
The body is ovate, slightly elongated (Kent, 1881-2) or ovoid (Penard, 1922; Kahl, 1926), the anterior end truncate, the posterior extremity conical. The young animal is often globular, size, 30-45 um, according to Kahl (1932). The membranelles of the adoral zone are long, spiralled more than one turn according to Kent (1881-2). The very fine, short somatic cilia form longitudinal rows at the left side of the body, whereas 4-5 oblique rows occur at the right side. Between these groups of rows there is a clear space with no cilia (Kahl 1932). Penard (1922) observed a soft capsule on the pellicle, but Kahl (1932) was not certain whether it is furnished temporally. The macronucleus has two segments. A contractile vacuole is located at one quarter or one-third of the body length from the anteriorly extremity (Kahl 1932) or in the posterior area (Kent 1881-2). A freshwater species. (ref. ID; 3389)

Measurements

30-80 um long. (ref. ID; 1618)
Size, 73 um and 50-80 um according to Kent (1881-2) and Kahl (1932), respectively. (ref. ID; 3389)

Strombidinopsis minima (Gruber, 1884) Lynn, Montagnes, Dale, Gilron & Strom, 1991 (ref. ID; 4917 redescribed paper)

Synonym

Strombidium minima Gruber, 1884 (ref. ID; 4917)

Improved diagnosis

Size ~30x25 um in vivo and ~25x20 um after protargol impregnation; broadly obconical or cylindrical, covered with a mineral envelope posterior to zone of external membranelles. On average 17 somatic kineties, 16 external membranelles, and 1 internal membranelle. Nuclear apparatus composed of a globular micronucleus between two broadly ellipsoidal macronuclear nodules. (ref. ID; 4917)

Comparison with related species and literature data

The mineral envelope characterizing S. minima is directly on the cell surface and thus dissimilar to a tintinnid lorica. Furthermore, it probably does not represent a progenitor of a lorica as a deposit of mucilaginous material and/or silt grains directly on the cell surface was never observed during lorica of formation in tintinnids (e.g. Laval-Peuto 1981). Strombidinopsis minima is easily identified by its epicortical cover of organic and inorganic material. Morphometry, however, shows distinct differences between populations in cell size, the number of kineties, the kinetids in a kinety, and number of external membranelles. There are five small congeners, which differ from S. minima mainly, or only, by the lack of the mineral envelope: Strombidinopsis azerbaijanica Alekperov and Asadullayeva, 1997 (three external membranelles extend into oral cavity, no internal membranelles mentioned); S. elegans Song and Bradbury, 1998 (26-27 external membranelles, 19-24 ciliary rows, oral cavity occupies 40-50% of cell length and ~40% of cell width); S. batos Lynn et al., 1991 (12-20x10-17 um in protargol preparations); S. sphaira Lynn et al., 1991 (13-15 external membranelles); and S. chilorhax Lynn et al., 1991 (without cover). Since the mineral envelope is easily lost during handling, the latter three species are possibly synonyms of S. minima. Strombidinopsis gyrans Kent, 1881, the type of the genus Strombidinopsis, is considered a synonym of Tintinnidium semiciliatum (Sterki, 1879) Kent, 1881, which lives in freshwater and occasionally leaves its lorica (Kahl, 1932; Foissner et al. 1991). Actually, S. gyrans has never been redescribed. Thus, the genus lacks a type species, as already recognized by Foissner et al. (1991), Lynn et al. (1991), and Aescht (2001). If a validly fixed type species is later found to have been misidentified, another species of the genus, which will best serve stability, may be selected and designated as the new type species (articles 67.9 and 70.3; ICZN 1999). Strombidinopsis acuminata Faure-Fremiet, 1924 is selected as the new type of Strombidinopsis because it (i) is an "old" species originally affiliated with this genus after live observation; (ii) is typical for the family Strombidinopsidae Small and Lynn, 1985 and its single genus, as defined by Lynn et al. (1991); and (iii) has been redescribed from protargol-impregnated material (Lynn et al. 1991; Dale and Lynn 1998). (ref. ID; 4917)

Neotype material

Strombidinopsis minima is neotypified from the shore of a salt lagoon on the Adriatic Sea coast near Venice, as no neotypes slides exist. Neotype slides have been deposited in the Biology Centre of the Museum of Upper Austria in Linz (LI), Austria, with the relevant cells marked. (ref. ID; 4917)

Strombidinopsis multiauris Montagnes & Taylor, 1994 (ref. ID; 7330 original paper)

Diagnosis

Cell conical, 95 um long (range, 42-140) and 45 um wide (32-64). External polykinetid zone (EPZ) comprised of 14-15 polykinetids, surrounding anterior end. External polykinetids (EPk) divided into two distinct ciliary zones; outer cilia 20-30 um long cilia extend at an angle of 90-45 degrees from longitudinal axis; inner cilia ~13 um long extend parallel to the longitudinal axis. Deep oral cavity acentrically placed within the circle of EPk. Interal polykinetid zone comprised of 4-5 separate polykinetids which lie in oral cavity. Large (3-5 um high) interpolykinetidal ridges strain darkly with protargol. Somatic kineties, 18 (14-25), equally spaced around cell, composed of 50-60 dikinetids (both with 7-9 um cilia), extend from oral region to posterior pole and may spiral around cell. Several (~10) somatic kineties may end subterminally along a thin bare patch (suture) ~20 um from the posterior. Darkly staining granules dispersed between kineties. Macronuclei, typically 2 (1-4), ovoid (8-12 um in diameter). (ref. ID; 7330)

Discussion of related species

Lynn et al. (1991) have rediagnosed the Strombidinopsidae. Strain 1509 possess the characters of this genus and is similar to three described species of Strombidinopsis: S. spiniferum (Leegaard, 1915) Lynn et al., 1991; S. acuminatum Faure-Fremiet, 1924; and S. cheshiri Snyder and Ohman, 1991. All three described species exhibit several characters with ranges that overlap with those of strain 1509: length, width, external polykinetids number, somatic kinety number, somatic cilia length, and macronucleus number. Further, all four species are elongate cells, which taper toward the posterior. There are several characters that distinguish strain 1509 from the three described species which it resembles. Two of the described species, S. spiniferum and S. acuminatum, have three independent internal polykinetids (IPk), while S. cheshiri and strain 1509 have four to five independent IPk. Strain 1509 also possesses four characters which distinguish it from all three described species. These features are:

1) The presence of large interpolykinetidal ridges. Interpolykinetidal ridges have not been reported for any other species of Strombidinopsis. Similar ridges (intermembranellear ridges) were used to describe the morphology of some strombidiids (Krainer 1991), and although such ridges are analogous in their position, we do not suggest they are homologous.
2) A division of the external oral ciliature (EPK) into two distinct zones. This is the first report of distinct differentiation of the EPk cilia in strombidinopsids. However, we have noted a similar ciliary morphology, to a much lesser extent, in S. cheshiri strain SPJSC. Therefore, this state may exist for other Strombidinopsis species but is accentuated in strain 1509.
3) The presence of darkly staining interkinetidal granules. Darkly staining somatic "granules" alone are likely not an acceptable diagnostic feature as their occurrence can be variable in other oligotrichs. However, other Strombidinopsis species are not pigmented as extensively as strain 1509. Thus, together with other features these granules help distinguish strain 1509.
4) The presence of many (>50) kinetosomes per kinety. It was not possible to determine the exact number of kinetosomes per kinety in our preparations, but there were always more than 50; this is more than the other three described species possess. Based on these differences we consider strain 1509 to be a new species. (ref. ID; 7330)

Etymology

The specific epithet, multiauris, refers to the many ear-like flaps around the anterior end of the ciliate. (ref. ID; 7330)

Time and locality of isolation

June, from 1 m depth, temperature of 20 degrees C, and salinity of 18 0/00 at Jerico Pier, English Bay, Vancouver, British Columbia, Canada (123 degrees 10'W, 49 degrees 17'N). (ref. ID; 7330)

Deposition of type material

Strombidinopsis setigera Stokes, 1885 (ref. ID; 1621, 3389, 4917)

Synonym

Strombidinopsis similis Stokes, 1891 (ref. ID; 1621); Tintinnidium setigerum (Stokes, 1885) Roux, 1901 (ref. ID; 3389)

Descriptions

The extensible body is elongated, sub-cylindrical or frequently conical. The anterior extremity is slightly oblique (Penard 1922), round or acuminated at the posterior. The peristomial area, where a lip-like membrane is furnished at the left edge, extends to the one third of the body from the posterior end. The entire body is covered with longitudinal rows of cilia very short, fine. These cilia are more dense in the posterior region. Beneath the AZM, there are long, tentacle-like cilia or bristles. The muscus material which covers the body is so slight that usually it is not noticeable. The globular macronucleus has 1-3 (Kahl 1932) or 2-3 (Penard 1922) micronuclei. Movement is very rapid. Found in pond water. (ref. ID; 3389)

Measurements

Size, 56 um and 65-75 um according to Stokes (1885) and Kahl (1932), respectively. (ref. ID; 3389)

Strombidinopsis spiniferum Lynn et al., 1991 (ref. ID; 7441)

Descriptions

Stomatogenesis: The oral area of the interphase cell consists of two kinds of oral polykinetids (OPk's). Strombidinopsis spiniferum and Strombidinopsis acuminatum typically have 15 external OPk's encircling the whole oral area. These will be referred to as Ex 1, Ex 2, ....Ex 15. In addition, S. acuminatum has 3-5 shorter internal OPk's and S. spiniferum has at least 3-4, termed Int 1, ...Int 5. Stomatogenesis may be divided into 8 stages. (ref. ID; 7441)

Stage 1. A small anarchic field of kinetosomes is first observed anteriorly on the dorsal side of the cells surface near a somatic kinety. Because the position of the anlage is approximately opposite to the parental cytopharynx, we have considered it to be dorsal. This origin is probably apokinetal because intimate contact with a somatic kinety was never observed. The two elliptical macronuclei (ca. 12x14 um) are located more anteriorly. No replication band was observed in the heavily stained nuclei.
Stage 2. The anarchic field has grown both larger and denser, and is typically situated between two somatic kineties. It is still on the cell surface, but later in this stage begins to sink inwards forming a small pit in the cell surface. When the Stage 2 anlage is seen from the side, some of the kinetosomes are apparently already ciliated, but the cilia are shorter than those of the somatic kinetids. In one cell of S. acuminatum, one of the macronuclei displayed a replication band.
Stage 3. The kinetosomes in the anarchic field have started to align themselves into OPk's. The organization of the kinetosomes into the OPk's begins on the left side of the anarchic field and progresses towards the right side (i.e. oriented with the oral area of the parent cell at the top and viewed as if from the outside of the cell on is dorsal surface). It was not possible to determined the numbers of rows of kinetosomes in the OPk's of the anlage as each OPk was stained very homogenously. The anlage sinks further into the cell, initially at the end where a portion of the anarchic field remains, and forms a cup-like invagination. In most of the Stage 3 cells, no marked differences were observed in the macronuclei, except in one cell, where the two macronuclei were attached to each other by a thin connection.
Stage 4. The OPk's have lengthened considerably and the anlage has become a cylindrical invagination beneath the cell surface. The anarchic field stil persists on the right posterior. The OPk's of the anlage are oriented transversely to the cell's longitudinal axis. The paroral membrane (PO) begins to form, and by the end of this stage is complete at its anterior end, where the kinetosomes form a compact line. In its posterior part, the kinetosomes are more loosely packed. The PO extend from the left side of the anteriormost OPk, termed EX 1 (Ex 1r), and extends initially in a curve towards the cell surface, "closes" the rim of the cylindrical invagination, and then turns downwards to the most posterior OPk in the anlage. This latter OPk, either Int 3 or Int 4-5, becomes the innermost internal OPk of the adult stage. In some samples of S. acuminatum, a replication band was observed in one macronucleus.
Stage 5. The anlage is still located beneath the somatic kineties and mainly oriented with its OPk's transversely to the cell's longitudinal axis. Apparently all the external (ca. 15) and internal (ca. 3-4) OPk's and a ciliated PO have now formed. However, a second row of granules, possibly kinetosomes, although they are less densely packed than the PO, extends from Int 3-4r deeper into the inpocketing. It is not clear whether this is a second part of the PO or the initial formation of an oral tube. During Stage 5, the anlage begins a complex movement composed of three major events: a spiraling process of the OPk's , a rotation of the complete anlage, and an unfolding of the OPk's. The posterior end of the anlage, Int 3-4, moves towards the anterior end of the anlage, Ex 1 (or both move towards each other) along the wall of the cylindrical invagination, closing the "barrel" in which the OPk's can be conceived of as staves. Accompanying this barrel-formation, the whole anlage invagination rotates approximately 90 degrees transversely to the cell's longitudinal axis, so that the right end sinks inwards and the left end turns outwards. As this occurs, the external OPk's begin to splay outwards, beginning to form the typical choretrich "closed" spiral. The OPk's are certainly ciliated at this stage. The PO is well differentiated and extends diagonally across the anlage from kinety Ex 1r to the left side of Int 3-4. In well-fed S. spiniferum, the macronucleus has not changed, but in starved S. acuminatum, a replication band was observed in both macronuclei.
Stage 6. The anlage has completed its approximately 90 degrees rotation so that the left end of the barrel is near the cell surface while the right end is rotated inwards into the cell. The OPk's nearest the surface have splayed open like an umbrella. The external OPk's of the anlage at this stage are composed of three rows of kinetosomes. Int 3-4 have moved closer to Ex 1 with the result that the PO is now aligned parallel to Ex 1 when seen from outside the cell, but it is apparently at a deeper level than Ex 1. The PO is now approximately transverse to the cell axis. The anlage is still beneath the cell surface of the parent cell, which is indicated by 2-4 complete somatic kineties that extend in the focal plane above it. In S. spiniferium, two macronuclei are commonly observed, but two cells in late Stage 6 had only one large macronucleus (size 21-24x13-14 um, n=20). No specimens of S. acuminatum were found at this stage.
Stage 7. Only strain 2 cells were observed in this stage. The anlage has now opened to the cell surface. The oral polykinetid Ex 15 is now partly aligned parallel to Ex 1. The main part of the PO now appears parallel to the cell's longitudinal axis. The internal OPk's and the PO are now situated in a deeper plane than the external OPk's. The completion of the differentiation of the PO through Stages 6 to Stage 8 has not been resolved. The somatic kineties have started to divide at Stage 7. As the dorsal part of the parent is adjacent to the dorsal part of the daughter cell, the division is a modified enantiotropic one. The large macrocucleus from the late Stage 6 has apparently divided into two (n=3 cells, 19-22x8-11 um). In one cell, the two large macronuclei were apparently still connected. No specimens were observed in cytokinesis.
The oral area in interphase cells. In the final stage, Stage 8, the mature oral apparatus includes a fully formed oral tube, extending from a region near Int 3-4. The PO forms almost a complete circle in the oral cavity. In most preparations, the PO had at least one marked bend on the side opposite to the internal OPk's. The average number of external OPk's was 15 in S. spiniferum. In some of the adult S. spiniferum and probably also in S. acuminatum, a total of three rows of kinetosomes could be seen in the external OPK's. In our preparation of S. acuminatum, one of the rows of kinetosomes in the OPK's was generally more heavily stained than the remaining two. In some preparations, one row was clearly separated from the other two giving the appearance of only two rows; this is probably a fixation artifact. At the outermost end of the OPk's, one of the rows was 1 or 2 kinetosomes shorter than the other two rows. A "zig-zag" pattern of cytoskeletal fibers was observed underneath the OPk's. It has been difficult to determine the numbers of rows of kinetosomes in the internal OPk's, but in several specimens of S. spiniferum the number apparently was three. The numbers of internal OPk's ranged between 3-4 in S. spiniferum and between 3-5 in S. acuminatum: The innermost in both species was sometimes difficult to resolve.

In several of the cultures of S. spiniferum, many monsters developed. These formed new mouths, but the cells were unable to complete cytokinesis, so that large specimens with two, three, and sometimes four mouths were observed. The somatic kineties of these cells were also abnormal. In some cultures, minicells were also observed. This was probably a result of "partial cannibalism" as observation of cultures often revealed that one specimen was sucking at the posterior part of another cell. These shorter cells have not been included in the measurements of the sizes. (ref. ID; 7441)

Redescription of S. spiniferum and S. acuminatum

Both species have a paroral that is usually easily seen in the anlage, but may be difficult to see in the oral area of interphase cells as it is situated beneath and close to the external OPk's. In their drawing of S. cheshiri, Snyder and Ohman (1991) showed an oral dikinetid that probably is the same as the paroral membrane observed by us. The PO may have been overlooked in other Strombidinopsis species at it has not been illustrated or described in some species. Strombidinopsis species have been illustrate and/or described as having two rows of kinetosomes in the external OPk's (Lynn et al. 1991; Montagnes and Taylor 1994). Our observations suggest that S. spiniferum, and probably S. acuminatum, has three rows of kinetosomes in the external OPk's, not two as previously reported. In our preparations, the three rows are only clearly seen in a few specimens as the OPk's usually were densely and rather uniformly stained. Finally, closer inspection of our preparations also revealed that both species may have more than three internal OPk's: up to four in S. spiniferum and up to five in S. acuminatum. This additional information on S. acuminatum, in particular, means that Strombidinopsis cheshiri Snyder & Ohman, 1991 is probably identical to S. acuminatum. According to Snyder and Ohman (1991), one of the main differences between these two species was that S. cheshiri had four internal OPk's compared to three reported for S. acuminatum by Lynn et al. (1991). Montagnes and Taylor (1994) redescribed S. cheshiri as having 4-5 internal OPk's. Otherwise, these two species are very similar in size, numbers of external OPk's, and internal OPk's, numbers of kinetids/kinety, and numbers of somatic kineties. Because of this, we conclude that S. cheshiri is a junior synonym of S. acuminatum. Snyder and Ohman (1991) noted that 87% of the their protargol stained specimens fixed with Bouin's would disappear following fixation, leaving only the wreath of the oral apparatus. This "bad habit" had also been observed for Strain 2 of S. spiniferum, which would completely disappear, leaving only a few wreaths, following fixation with formalin with added acridine orange. However, fixation with Bouin's or with Lugol's gave similar results to live counting. These observations suggest that Strombidinopsis species may often be underestimated in determinations of ciliate cell densities based on samples fixed with certain fixatives. (ref. ID; 7441)

Examined material

Samples of three strains of S. spiniferum came from cultures isolated by T.D.: Strain 1 came from the Barents Sea (Station 898, AUG, 1985, 78 degrees 35'N, 28 degrees 29'E) at a depth of 10 m in water of 2 degrees C and a salinity of 33.3 0/00; Strain 2 came from the Barents Sea (Station 50, APRIL 1986, 73 degrees 11'N, 30 degrees 19'E) in surface water of -1 degrees C; and Strain 3 came from coastal waters outside Bergen (APRIL 1987, 60 degrees 16'N, 5 degrees 13'E) in surface water of 3-4 degrees. Strain 2 was also used to redescribe S. spiniferum (Lynn et al. 1991). Most of the observations for the current study were based on Strain 3, and it is indicated in the text when Strains 1 or 2 were used. (ref. ID; 7441)