Opisthonecta

Opisthonecta Faure-Fremiet, 1906 (ref. ID; 2014)

Class Oligohymenophora: Subclass Peritricha: Order Peritrichida: Suborder Sessilina (ref. ID; 2014)
Suborder Sessilina Kahl (1930-1935): Family Opisthonectidae Foissner, 1975 (ref. ID; 7483)
Family Opisthonectidae Foissner (ref. ID; 4813)

[ref. ID; 2014]
Free-living peritrich which never settles on a substratum or develops a stalk. The peristome with 2 membranelles winding anticlockwise to the cytostome is directed forwards when the barrel-shaped peritrich swims, aided by a permanent aboral ring cilia. On the inner lip of the peristome there is an epistomial membrane. The macronucleus is C-shaped. The genus is most easily mistaken for Telotrochidium which does not possess and epistomial membrane. It could also be confused with Hastatella and Astylozoon which are without an aboral ring of cilia.
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)

Opisthonecta bivacuolata Foissner (ref. ID; 3698, 4259) reported author and year? (ref. ID; 472, 7483)
Opisthonecta dubia (ref. ID; 7483)
Opisthonecta henneguyi Faure-Fremiet, 1906 (ref. ID; 4488, 4610, 4613, 7753) or 1924 (ref. ID; 4259) reported author and year? (ref. ID; 191, 1629, 7483)
Syn; Opisthonecta patula Foissner, 1975 (ref. ID; 4610, 4613, 7483)
Opisthonecta matiensis Martin-Cereceda et al., 1999 (ref. ID; 7483 original paper)
Opisthonecta minima (ref. ID; 4259, 7483)
Opisthonecta patula (ref. ID; 4259, 4610, 4613, 4813)
See; Opisthonecta henneguyi (ref. ID; 4610, 4613, 7483)

Opisthonecta henneguyi Faure-Fremiet, 1906 (ref. ID; 4488, 4610, 4613, 7753) or 1924 (ref. ID; 4259) reported author and year? (ref. ID; 191, 1629, 7483)

Synonym

Opisthonecta patula Foissner, 1975 (ref. ID; 4610, 4613, 7483)

Descriptions

Opisthonecta henneguyi, is a free-swimming peritrich with a hemispherical end limited by the trochal band and an oblong adoral end. This ciliate has a tuft of cilia in its oral region of a length more than twice that of the haplo- and polykineties, the "flamme epistomienne" according to Faure-Fremiet, or the "epistomial membrane" according to other authors (Bradbury 1965; Foissner 1975; Kofoid & Rosenberg 1940; Lom 1964). The dimensions of the specimens found by us vary considerably if they are measured on cells fixed with osmium tetroxide without a coverslip or on impregnated cells with a coverslip. The large horse-shaped macronucleus is situated in the middle of the ciliate. The micronucleus is located in the oral end of the organism, close to the buccal cavity. The number of contractile vacuoles of this species is two and sometimes three. These vacuoles open into the infundibulum at different levels, and the cytoproct opens in the ventral side of the infundibulum closer to its overture. The cysts range between 56 and 66 um in diameter and are spherical with a refringent wall of 3-3.5 um in thickness. (ref. ID; 4259)

Oral infraciliature: The oral infraciliature is formed in its beginning by a haplokinety with kinetosomes disposed in a zigzag pattern and a polykinety three kinetosomes wide; both these structures run parallel from their beginning in anti-clockwise direction one and a quarter times around the peristome before entering the buccal cavity. Near the origin of the haplo- and polykinety, several kinetosomes forming the infraciliature of the epistomial membrane are clearly visible. Near the buccal overture the haplokinety and the polykinety separate, and while the polykinety enters the cavity directly, the haplokinety spirals around the infundibular overture and hence moves 180 degrees out of line with its companion. Where these two structures are separated, we observe the germinal kinety, which begins very near the haplokinety. It is composed of kinetosomes very close to each other, and it accompanies the haplokinety within the infundibulum. The first polykinety enters the infundibulum in an oblique trajectory forming the first peniculus, and in its first turn a second peniculus, with three rows of kinetosomes, joins it. These run parallel and close together, and the third peniculus, also of three rows of kinetosomes, joins the two others at the end of the buccal cavity. The first peniculus goes two and a half times around into the infundibulum. (ref. ID; 4259)
Aboral infraciliature: The trochal band is 1.5 um approximately in width, and its infraciliature is formed by many short oblique rows of six kinetosomes each; three fibrillar systems begin from this belt. Short fibers of about 2 um in length extended from each kinety and go towards the oral pole; they form the system of orally directed fibers. Longer fibers of 10-15 um in length also extend from each kinety, but in an aboral direction, and occupy approximately half of the aboral disc; these fibers form the system of aboral fibers. At a deeper level, other fibers depart from each one of the kinetosomes of the trochal band forming an angle of about 90 degrees with the kineties; we have called them the system of oblique fibers. It is not possible to establish the exact length of these fibers, because the fiber of each kinetosome reaches that of the next kinetosome located at its right, forming a thicker common fiber. The scopula is located at the aboral pole, and it is formed by a ring of eight to ten kinetosomes. (ref. ID; 4259)
Argyrome: The argyrome is formed by fine circular striations which cover the whole organism except the peristomial disc. The number of silverlines in our species varies between 60 and 75 between the peristomial disc and the trochal band and between 40 and 50 from the trochal band to the scopula. The lines of the argyrome placed between the peristome and the trochal band are further apart than those located between the trochal band and the scopula. It is possible to observe some delicate argentophilic dots near these striations. (ref. ID; 4259)
Myonemic system: The myonemic system of O. henneguyi is located in two regions: the oral and the aboral ones. The oral myonemic system is formed by fibrous rings 60-70 um in diameter, which surround the peristome posterior to the spiral of the peristomial infraciliature, and by a group of longitudinal fibers which extends from the peristomial disc. The number of ring fibers varies between four and six, and the most adoral one is always the thickest one. The second oral myonemic system is formed by longitudinal fibers which originate in the peristomial disc, reaching their greatest diameter when they have extended past the peristomial infraciliature and the oral myonemic ring. At this level, counting around the circumference, the number of fibers is 20-25, and they undergo numerous ramification more posteriorly. The aboral myonemic system is much simpler and more delicate. It is formed by 10-15 fibers which radiate from an annular fiber within the ring of kinetosomes in the scopula. These fibers divide into thinner branches tapering toward the trochal band, where they are hidden by the adoral fibers emerging from the band. (ref. ID; 4259)

Stomatogenesis. (ref. ID; 7753)

Comments

The size of fixed specimens is smaller than those in other studies of O. henneguyi (Faure-Fremiet 1906 & 1924; Kofoid & Rosenberg 1940; Lynch & Noble 1931), O. patula (Foissner 1975), O. minima (Foissner 1975), and O. bivacuolata (Foissner 1977). The stained specimens have a similar length to O. hennegyi (Faure-Fremiet 1906 & 1924; Lynch & Noble 1931) and O. patula (Foissner 1975), but O. patula is broader than it is long, and the length of its infundibulum is greater than in our species. In our species, the number of contractile vacuoles, two or three, is the same as in O. henneguyi (Kofoid & Rosenberg 1940) and O. bivacuolata (Foissner 1977), and the diameter of the living cysts found by us very similar to that observed in O. henneguyi (Kofoid & Rosenberg 1940). This last datum is, in our opinion, less variable than the other ones. On the other hand, Foissner (1975) considers that O. henneguyi described by Lynch & Noble (1931) and O. henneguyi described by Kofoid & Rosenberg (1940) are synonyms of O. patula and O. minima, respectively. The peristomial infraciliature of O. henneguyi has been described after both light and electron microscopy studies (Bradbury 1965; Kofoid & Rosenberg 1940; Lynch & Noble 1931; Rosenberg & Grim 1966), and we disagree only with Fernandez-Leborans (1982). This author described a short "undulating membrane" near the infundibular overture, which we have never seen in our preparations. The epistomial membrane, considered by Foissner (1975) as a systematic character separating the genera Opisthonecta and Telotrochidium has bee described in O. henneguyi (Bradbury 1965; Kofoid & Rosenberg 1940; Lynch & Noble 1931) at the opening of the buccal cavity. We observed this structure at the beginning of the peristomial infraciliature, more separated from the infundibular overture that in Telotrochidium sp. (=O. minima) (Fernandez-Leborans 1982). We could not find any fibrillar system associated with it. As concerns the "motorium" (Kofoid & Rosenberg 1940), we believe that it corresponds to the zone where the germinal kinety starts, a more argentophilic zone than the rest located at the entry of the buccal cavity. This zone corresponds also to the beginning of the infundibular crests observed by Bradbury (1965) and Rosenberg & Grim (1966). The germinal kinety, described in Telotrochidium sp. (=O. minima) (Lom 1964) as a short row of kinetosomes at the entry of the infundibulum beside the haplokinety, appears in our preparations as a kinety with kinetosomes that are close together. This kinety and the haplokinety could correspond to the two parallel haplokineties reported by Bradbury (1965). While the pristomial infraciliature has been easily observed by authors (Bradbury 1965; Kofoid & Rosenberg 1940; Lynch & Noble 1931; Rosenberg & Grim 1966), the infundibular infraciliature has proved more difficult. Kofoid & Rosenberg (1940) observed that three or more rows of kinetosomes, inside the infundibulum, join the first polykinety, and propose that this complex is a peniculus. Bradbury (1965) observed that a three kinetosomes polykinety also joined the first one, though she pointed out that in some cases there are seven or eight rows of kinetosomes in the cytostome instead of six, and other authors (Foissner 1975; Lom 1964; Rosenberg & Grim 1966) described a third polykinety in this genus, with three kinetosomes also, which joins the former two close to the cytostome. Although all authors have observed the trochal band in this genus, they have not seen its infraciliature clearly. With our method of silver impregnation, we do not observe the thick line of argentophilic dots, situated beneath the trochal band, that Foissner (1975) considers as a characteristic of the genus Opisthonecta; however, using electron microscopy, we have observed in O. henneguyi (Guinea, Gil & Fernandez-Galiano 1986) that both sides of the trochal band are limited by pellicular pores. The fibrillar system formed by the oral fibers coincides as far as their location with the fibers described by Bradbury (1965) as the oral prolongation of the diagonal rod; however, the ones observed by us do not curve to the left ending above the second diagonal row to the left of its origin, but they have a right trajectory, parallel to the longitudinal axis of the ciliate, ending about 2 um from their origin. The aboral fibers coincide with those observed by Bradbury (1965) as the aboral prolongation of the diagonal rod and with the "radial fibers" described by Kofoid & Rosenberg (1940) in its complicated "neuromotor apparatus". The third fibrillar system, that of the oblique fibers, corresponds, we believe, to the one that Bradbury (1965) mentions as striated fibers, of unspecified origin and extension. We disagree with the interpretation of this fibrillar system by Fernandez-Leborans (1982) in Opisthonecta sp. This author stated that these fibers emerge one from each kinety, as in the two previous systems, from the aboral edge of the belt towards the left. We have observed that these fibers depart from each of the kinetosomes of the trochal band towards the right. In our opinion, this fibrillar system is formed by the kinetodesmal fibers of the trochal band kinetosomes. The argyrome of our species is similar to those described in other species of this genus. The silverline number of this species is greater than those in O. minima and O. dubia (Foissner 1975), and it is very similar to that found in O. patula (Foissner 1975). The oral myonemic system of our species coincides with that described in O. henneguyi (Kofoid & Rosenberg 1940; Lynch & Noble 1931), but it differs from those in O. bivacuolata (Foissner 1977) and Opisthonecta sp. (Fernandez-Leborans 1982). The oral myonemic ring has a larger diameter than Opisthonecta sp. The oral myonemic ring has a larger diameter than Opisthonecta sp. (Fernandez-Leborans 1982), and the longitudinal fibers do not finish in the myonemic ring as in that species but in the peristomial disc. Moreover, these longitudinal fibers are not clearly interconnected with the trochal band as in Opisthonecta sp. (Fernandez-Leborans 1982) and O. bivacuolata (Foissner 1977). The aboral myonemic system also differs from those observed in Opisthonecta sp. (Fernandez-Leborans 1982) and O. bivacuolata (Foissner 1977). In our species, the fibers radiating from the scopula extend towards the trochal band in branch-like divisions, but we do not observe their connection with the trochal band. This system is similar to that described by Kofoid & Rosenberg (1940) as "aboral retractor fibrils". The differences in the myonemic system of O. bivacuolata (Foissner 1977) and our species may be due to the different impregnation methods used, but Opisthonecta sp. (Fernandez-Leborans 1982) impregnated with our method shows a myonemic system very similar to that observed in O. bivacuolata (Foissner 1977). (ref. ID; 4259)

Type locality

Opisthonecta henneguyi Faure-Fremiet was taken from a stream in the "Dehesa de la Villa" (Madrid). (ref. ID; 4259)

Opisthonecta matiensis Martin-Cereceda et al., 1999 (ref. ID; 7483 original paper)

Diagnosis

In vivo 45-72.5 um (average 58.2 um)x25-40 um (average 31.3 um); amphora-like cell with oral region of smaller extent than aboral one, which is slightly inclined towards the dorsal side of the cell; ventral side shorter than dorsal. Epistomial membrane on a protuberance above the vestibular opening. Buccal cavity conspicuous and extends down about 2/3 of cell length, with one single contractile vacuole located near ventral side of the vestibule. Silver line system of 147 lines. (ref. ID; 7483)

Descriptions

Opisthonecta matiensis has a typical amphora-like morphology, but the cell size is moderately variable. Starved organisms are usually small than those well-nourished. A refractile contractile vacuole opens into the ventral side of the infundibulum. The cytoplasm appears colourless with numerous food vacuoles of granular appearance. In culture, O. matiensis swims with the aboral pole forward showing rapid rotational movements around the main body axis. Change of direction occurs by whole inclination of the body. Swimming is sometimes interrupted for feeding; in that case, the cells are anchored to the substrate (Petri dish bottom) by the posterior pole without, however, forming a stalk. (ref. ID; 7483)

Nuclear apparatus: A single macro- and micronucleus are present. The macronucleus is easily observed in vivo and has a characteristic narrowing in its central portion; it is situated almost parallel to the longitudinal cell axis, although other orientations sometimes were found, probably due to coverslip pressure. A spherical micronucleus is in the anterior half of the organism. (ref. ID; 7483)
Oral infraciliature: A polykinety three kinetosomes wide and a haplokinety with kinetosomes arranged in zigzag occur at peristomial level. The polykinety and haplokinety make 1+1/4 turns around the peristome before entering the buccal cavity. Near the buccal overture, the haplokinety and the polykinety are separated and both dive downwards. A short stretch of kinetosomes (germinal kinety) surrounds the entry of the infundibulum, very close to the haplokinety. At infundibular level, the polykinety forms the first peniculus (P1) (= infundibular polykinetid), and a second peniculus (P2) arises parallel to the first one. Both peniculi (P1 and P2) make a turn in the infundibulum. At the bottom of the buccal cavity a third peniculus (P3) joins the other two. All peniculi are formed by three rows of kinetosomes. A large, branched pharyngeal bundle fiber arises from the cytostome, spreading through the cytoplasm. This bundle is composed of microtubules, as revealed by immunofluorescence microscopy using the antibody GT335, which is specifically targeted to a post-translational modification (polyglutamylation) of tubulin. (ref. ID; 7483)
Aboral infraciliature: This consists of a belt of short oblique kineties (trochal band) and a field of 15-20 kinetosomes located at the aboral pole of the ciliate (scopula). The trochal band has an average width of 1.7 um and its kineties include six kinetosomes each. It is bordered by one pellicular fold on its oral side and by two pellicular folds on the aboral one. These folds are supported by microtubules. Three rows of pellicular pores occur: one row behind the oral pellicular fold and two rows limiting the aboral ones. A third pore row could be also present between both aboral folds. Three fibrillar systems originate from the trochal band. (i) Oral fibers (average 3.7 um in length) emerge from the left side of the uppermost kinetosome of each kinety. (ii) Aboral fibers arise from the right side of each kinety and extend towards the aboral pole. These fibers greatly vary in length (average 3.1-8.3 um) and have no specific arragement, so no particular areas of the trochal band are occupied by a specific type-size of aboral fiber. (iii) Oblique fibers, which were observed only in the electron microscope, are on the right side of all the kinetosomes and go obliquely towards the aboral pole. (ref. ID; 7483)
Myoneme system: This system consists of an inconspicuous ring in the peristomial collar, and a set of longitudinal branched fibers extending from the peristomial area to the trochal band. Radial fibers stretch out from the scopula to the trochal band. (ref. ID; 7483)
Silverline system: This system is formed by circular lines (= pellicular striae), averaging 129 between the peristomial disc and trochal band, and 18 between this band and the scopula. A high number of argyropilic dots are attached to the silverlines. Average inter-silver line distance is 0.1 um, although the silverlines placed between the trochal band and the scopula are further apart than those located between the peristome and the trochal band. In the electron microscope, the silverlines correlate with fine fibres underneath the cortical ridges. (ref. ID; 7483)
Conjugation: Conjugation was observed in O. matiensis, but was not studied in detail. The process takes placed about 72 h after the cells are inoculated in fresh culture medium. It is anisogamontic: macro- and microconjugants are formed. Microconjugants move quickly in the culture until they attach to the ventral area of a macroconjugant at its aboral pole. The size of microconjugants ranged from 15-25 um, and they showed a conspicuous trochal band with long cilia. Their peristome was always contracted, so that the oral infraciliature could not be observed. (ref. ID; 7483)
Cysts: Occasionally, we found some oval structures which tended to group together. These could be precystic stages as they were always found in starving cultures. However, no vegetative cells occurred when these structures were inoculated in a medium enriched with nourishment (bacteria). (ref. ID; 7483)

Notes

Opisthonecta matiensis n. sp. differs from the four previously described species of Opisthonecta (O. henneguyi, O. bivacuolata, O. dubia, O. minima) in : (1) the body shape, because O. matiensis n. sp. presents a typical amphora-like morphology not shown by the other Opisthonecta species; (2) the smaller size of the cell; (3) the presence of a single contractile vacuole since, with the exception of O. minima, the other species of this genus have 2-3 vacuoles and (4) the total number of silverlines, which is higher than in the other species. Foissner (1975) also considered the presence of a row of very close argyrophilic dots below the trochal band as an important diagnostic character of the genus Opisthonecta. Using electron microscopy, we have in fact observed two (even three) rows of pellicular pores (argyrophilic dots) beneath the trochal band and one row above it. The pores are very close to the pellicular folds limiting the trochal band. This pattern in the ultrastructure of the trochal band is very similar to that indicated in Opisthonecta henneguyi (Guinea et al. 1986) except that in O. matiensis up to three pore rows can be observed below the trochal band. Guinea et al. (1986) also pointed out that the pellicular folds are supported by microfibrils. In O. matiensis we have observed that the folds are underlain by microtubules. Our results concerning the peristomial infraciliature coincide with those obtained in O. henneguyi by Guinea and Fernandez-Galiano (1987) using the same impregnation method, and by Augustin and Foissner (1992) in protargol-stained specimens. The infundibular infraciliature is, however, different: in O. matiensis, the polykinety performs only one turn inside the buccal cavity while in O. henneguyi it describes two turns. Moreover, the germinal kinety of O. is observed only at the entry of the vestibule. This arrangement of infundibular infraciliature is in accordance with that reported by Lom (1964) in Telotrochidium sp., later considered as a synonym of O. minima, and with that described by Berger et al. (1984) in Telotrochidium cylindricum. A postpharyngeal fibre bundle extends from the cytostome along the cytopharynx. This bundle was first observed by Kofoid and Rosenberg (1940) in O. henneguyi (O. minima according to (Foissner 1975)), who thought it acted as a guide for the food vacuoles. Bradbury (1965) showed by electron microscopy that these fibrils are part of the pharyngeal wall, and also assigned them a function in guiding the food vacuoles through the cell. Later, Berger et al. (1984) and Foissner (1976) also noted the presence of a long fiber arising from the cytostome in two species of the genus Telotrochidium (T. johanninae and T. cylindricum). However, none of these studies has revealed the nature of these fibers and it has only been indicated that they stained well with nigrosin (Bradbury 1965). In this study, we have demonstrated that, in O. matiensis, the pharyngeal bundle consists of microtubules since they were decorated by an anti-tubulin antibody (antibody GT335). This experiment was paralleled with the species O. henneguyi (data not shown) and the results obtained were similar: a long bundle of fibers emerged from the cytostome and generally continued in a long curve towards the other side of the body. As regards the aboral infraciliature, our results generally match previous studies. We also found three fibrillar systems extending from the trochal band, but their size differs from those obtained in other species. In O. matiensis, the oral fibers are larger than in O. henneguyi, while the aboral ones are much smaller. Moreover, in O. henneguyi, the aboral fibers are more homogeneous in length than in O. matiensis. The scopula of O. matiensis is composed of a larger number of kinetosomes (15-20) than in O. henneguyi (8-10). The myoneme system of O. matiensis is similar to that of other species. However, the fibrous ring in the peristomial collar is thinner than those described in O. henneguyi (Guinea et al. 1987) and Opisthonecta sp. Moreover, the longitudinal myoneme fibers extending from the peristomial disc in O. matiensis seem to be more branched than in O. henneguyi (Guinea et al., 1987). These fibers, as in Opisthonecta sp. and O. bivacuolata (Foissner 1978), are interconnected with the trochal band. The aboral myoneme system is similar to those previously described in Opisthonecta sp. and O. bivacuolata because the ramifications extending from the scopula also reach the trochal band. The silverline system of O. matiensis is very similar to that described in other species of the genus. However, the number of silverlines is greater than those found in any other species of Opisthonecta. Furthermore, the silverline pattern is different from that observed in O. henneguyi (Guinea et al. 1987). The silverlines located between the trochal band and the scopula are further apart than those between the peristome and the trochal band. Concerning the ultrastructure of the silverline system, our results confirm the findings of Foissner (1975), who first correlated the fibrillar structures with the argyrome in peritrich ciliates. (ref. ID; 7483)

Etymology

matiensis refers to the name of the locality, Las Matas, site of the wastewater treatment plant where the species was isolated. (ref. ID; 7483)

Type locality

Inlet water to a sewage treatment plant receiving domestic inputs from north of Madrid, Spain. (ref. ID; 7483)

Type specimens

A culture is deposited in the Culture Collection of Algae and Protozoa (Ambleside, UK). Accession number: CCAP 1655/2. (ref. ID; 7483)