The World of Protozoa, Rotifera, Nematoda and Oligochaeta
Notholca
Notholca Gosse, 1886 (ref. ID; 7815)
Class Monogonontaet: Order Ploimida: Family Brachionidae (ref. ID; 6806)
Class Rotatoria: Order Ploimida: Family Brachionidae (ref. ID; 7097)
ref. ID; 826
The first level of characters corresponds to the subgenetics or superspecific categoty, and for such as Notholca squamula, Notholca acuminata, Notholca striata, Notholca caudata, Notholca cinetura, Notholca lamellifera, Notholca triarthroides the most suitable term is 'group species'. Characters of the second level correspond to the rank 'species'. Characters of the third level correspond to the rank 'subspecies'. The term "Artgruppe' and 'Formenkreis' used Koste (1978) seem of little use, since various meanings have been attributed to then at different times (Kleinschmidt 1900; Rensch 1929). The use of the above mentioned names makes the problem of limits and criteria of rotifer species still more urgent. Kutikova proposed three separate complexes of species; complex I without posterior spines on the lorica, complex II with caudal spines developed to some extent; complex III with well-developed posterior spines. The parallelism I morphological variability allows him distinguish the characters typical of species complexes, as well as of separate species.
Complex I (without posterior spines on the lorica)
N. lapponica, N. squamula michiganensis, N. squamula salina, N. squamula mulleri, N. jugosa, N. laurentiae
Dorsal plate with dotty marking; N. cristata, N. kostei
Large size; N. frigida
Posterior margin of ventral plate protrusible + lorica with wavy ridges; N. verae
Complex II (with caudal spines developed to some extent)
N. acuminata extensa, N. acuminata marina, N. angulata, N. complexa, N. labis limnetica, N. psammarina
Large size; N. caudata, N. cinetura, N. determinata, N. gaigalasi, N. grandis, N. lamellifera, N. latityls
Posteriormargin of ventral plate protrusible; Notholca haueri (dorsal plate with dotty marking), N. intermedia, N. kozhovi rectospina
Caudal spine forked + dorsal plate with dotty marking + lorica with wavy ridges; N. jaonica, N. jaonica kisselevi
Complex III (with well-developed posterior spines)
N. cornuta, N. striata, N. striata liepettersini, N. striata bipalium
Large size; N. baicalensis, N. jasnitskii, N. olchonensis, N. olchonensis deviata, N. triarthoides
Notholca japonica, Notholca foliacea, Notholca kostei, Notholca olchonensis have characters of Complex I, II, III + dotted sculpture of the lorica.
Species of the genus Notholca include a great number of Baikalian endemics (11 endemic species out of a total of 39 species in the genus). The fauna of Lake Baikal consists of two complexes; one is usually termed palaecolimnic, being a more ancient complex closely associated with the inhabitants of oligotrophic water-bodies of the Holarctic, while the second one is called mesolimnic, and originated later from remnants of the faunas of no longer-existing waterbodies, originally located in the Central Asian and Mongolian territories in the upper Cretaceous. (ref. ID; 826)
ref. ID; 1663
Dorsal surface of lorica longitudinally striated, ventral lorica without keel. With one or no posterior spine, and with six short to medium anterior spines. (ref. ID; 1663)
ref. ID; 1923
Common in ponds and other small waters, not common in lakes plankton. Some authors recognize a subgenus Argonotholca for the species with ventral keel. Notholca is polytypical species. Common in ponds and other small waters, not common in lakes plankton. Some authors recognize a subgenus Argonotholca for the species with ventral keel. (ref. ID; 1923)
ref. ID; 3334
In this genus the lorica is a box-like structure of two plates. Two or three pairs of spines of differing lengths are symmetrically arranged on the anterodorsal margin of the lorica. The members of this genus are free swimming. They lack a foot or ventral attachment discs. The mastax has malleate trophi. (ref. ID; 3334)
ref. ID; 4594
Lorica of two spoon-like plates united laterally; with six spines in front. Dorsal surface striated longitudinally. (ref. ID; 4594)
Notholca acuminata-group
ref. ID; 3053
The species are characterized by a posterior extension on the dorsal plate, which varies greatly in length. The group consists of four species: N. acuminata (Ehrenberg) (= N. a. lacustris Focke). N. caudata Carlin, N. labis Gosse, and N. marina Focke. An absolute, well-defined distinction between these species cannot be given, as morphological intermediates do occur between all of them in some way, and there is still uncertainly about their taxonomy. The following criteria can, however, normally be taken into consideration with identifying these species: 1. The end of the posterior extension is sharply pointed in N. caudata and straightly cut off or somewhat rounded in the others. 2. The posterior extension tapers fairly continuously from the rest of the lorica in N. acuminata and is discontinuously set off (often widening out at the end) in N. labis and N. marina (mostly not when very short). In N. caudata all variations occur. 3. The posterior margin of the ventral plate is almost straight in N. acuminata and convexly curved in the others. 4. The ratio body length/breadth is smaller in N. labis than in the others. (ref. ID; 3053)
This group consists of N. salina Focke and N. squamula (Muller). The former was separated from N. squamula by Focke (1961) as a morphologically different marine subspecies which he called N. s. salina, while he called the freshwater subspecies N. s. mulleri. A genetic difference between them was shown by the fact that the former, when adapted to freshwater, could live there for several generations without changing morphologically. Bjorklund think it is more correct to consider the two forms as separate species. The freshwater species should then keep the old name, N. squamula, as this is the one described and figured by Muller (1786). It may also be noted that the name N. striata erroneously has been used for N. squamula by almost all authors until Carlin (1943) cleared up this mistake. The two species are distinguished by the relative length of the dorsal spines. In N. salina the median spines are longest and the lateral shortest, or, exceptionally, equally long as the intermediate ones. In N. squamula the intermediate spines are always the shortest and the other ones markedly longer; the median ones mostly the longest. While the marine species is rather uniform in size and shape, the freshwater one varies a good deal both in size and spine length, and different subspecies or varieties of this species (N. s. evensi Gillard, N. s. frigida Jaschnow) have been described. Transitional forms seem to been found between the smaller forms, but the large fridiga form is supposed by Carlin to be a polyploid form. (ref. ID; 3053)
All specimens with mobile lateral spines on the posterior part of the lorica have hitherto by almost all authors been referred to one and the same species. Since Carlin (1943) cleared up the earlier mistake of using the name N. striata for N. squamula, the name N. striata has been used for these lateral-spined forms. Few authors, however, seem to have found more than one of these forms at a time, and two size groups, when they occurred, have mostly be considered to belong to a single species with a very great variation. The first who, since their original description (Muller 1786), considered the two size groups as different species, was Focke (1961). There was no overlapping in size, and he also pointed out differences in the relative length of the median and lateral dorsal spines, although this was not an absolute feature. The smaller species was N. striata (Muller) while the larger one was considered identical with Muller's Brachionus bipalium. Although no lateral spines wee shown on Muller's figures. These spines may have been overlooked, however, as this is easily done when they are lying along the lorica. This is the case also with two of Muller's figures of N. striata, while the third one shows the spines. Few later authors have agreed with Focke, however, in separating the two forms as species. They have claimed to have found intermediate sizes, or referred to others who seemed to have found such, but hitherto no one has made a biometrical analysis of a larger material where more parameters and combinations of such are used. As Bjorklund have a rather large material from different habitats and from areas far apart, from one area also through the year, the analysis made should be fairly descriptive and significant. The two parameters which in combination best showed the differences between the forms were the body length and the length of the mobile lateral spines. Two markedly separate size groups with related to body length can be distinguished. The larger size group is N. bipalium. The smaller size group, however, contains two groups of points, which as regards the Espegrend and the Hudson River material are quite separated, although the groups of points from each area do not corresponded very well to each other. The Tvarminne material constitutes a single group which corresponds with that of smallest-sized group from Hudson River, and the specimens have sizes between and overlapping with the two Espegrend groups. However, as the Espegrend material which is by far the richest and also is taken throughout the year, is so clearly divided into two groups of smaller size, and the two forms also occur together without overlapping, two different species must be present. That the size relations of the forms found in the other areas were partly different from the Espegrend forms, may be due to local variations (this is seen for most of the Notholca species studied). The "shortspined" form is identical with N. striata. The "longspined" form has therefore been given a new name, N. liepetterseni. (ref. ID; 3053)
Cosmopolitan in its distribution and displays high polymorphism.
The lorica is narrow and has a posterior extension sometimes bringing to mind the "labis" form. (ref. ID; 1402)
N. acuminata was by Focke (1961: see ref. ID; 3281) separated into two subspecies, the freshwater N. a. lacustris and the marine N. a. marina. They occurred together in a few localities of low salinity where also some "intermediate" forms were found which he considered as hybrids or descendents from such. This he regarded as a criterion of their subspecies status. He did not, however, give any description or figure of such a hybrid, and as the discriminating features between the two subspecies were not absolute, and both forms could vary considerably in size and shape, it is difficult to establish which is a hybrid or which is only a specimen with in the form variation of each of the two "subspecies". Bjorklund do not feel convinced that they really are subspecies as no crossing experiments have been made to verify Focke's theory. If they were, they should have unlimited interfertility, and it is not reasonable to believe that when they occur together they would have remained separated into two different forms with only a few intermediates. Taking into account the crossing experiments by Ruttner-Kolisko (1969) which indicates that sexual reproduction in the Rotatoria serves the production of resting eggs rather than gene recombination (the offspring was morphologically similar to the mother form), Bjorklund think it is most correct to consider the two forms as separate species. As the typical freshwater form is the one figured and described by Ehrenberg (1938) as Anuraea acuminata, acuminata must still be the name of this form, and not lacustris as Focke has called it. Bjorklund found that a fairly food separating feature between N. acuminata and N. marina was the body length in relation to the length of the posterior extension. Mostly either the body length or the extension or both were smaller in N. marina, but there is a fairly broad zone of overlapping in the Espegrend material. The two sizes mentioned were correlated in N. acuminata, while in N. marina they varied quite independently. In order to distinguish the two species, one often has to study both the size and shape of the different parts of the lorica (and also the trophi) in combination on a number of specimens: 1. N. acuminata has mostly a greater body- or extension length or both than N. marina. 2. In N. acuminata the extension mostly tapers more continuously from the rest of lorica than in N. marina, except when the extension in the latter is very short. 3. N. acuminata has mostly an almost straight posterior margin of the ventral plate while in N. marina it is covexly curved. 4. N. acuminata has mostly longer dorsal spines in relation to the posterior extension than N. marina. 5. N. acuminata has mostly a protuberance on the end of the manubria, while N. marina mostly has none. (ref. ID; 3053)
Lorica slightly produced behind into a more or less long, spoon-shaped point. Freshwater species, often found in brackish water, especially near the border of the Baltic and North Sea. Littoral. (ref. ID; 4594)
Comments
The variation in N. acuminata in the localities investigated is considerable, temporal as well as local variation having been observed. The temporal variation will be treated first in this context. (ref. ID; 3235)
It varied much in shape; in freshwater pools typical N. a. lacustris Focke occurred, with variable lengths of the posterior extension of the lorica; in brackish pools the specimens always had short extensions, but otherwise showed characters of both N. a. lacustris and N. a. marina Focke. In the landlocked fjords and inlets there were also intermediate forms, along with some specimens typical of N. a. marina with variable length of the posterior extensions. (ref. ID; 3573)
Measurements
Total length 210-260; breadth 80-100; stalk length 50-170 µm. (ref. ID; 1402)
Length of lorica 200-290; breadth of lorica 80-105; length of anterior middle spines 30-35 µm. (ref. ID; 3275)
Total length 135-300 µm. (ref. ID; 4594)
Notholca acuminata var. extensa Olofsson, 1917 (ref. ID; 1345, 1402) or 1918 (ref. ID; 2841, 3688)
With diamond-shaped lorica and lateral angles is a typical transitional form between species of complex II and III. Endemic species (the border region of Central Asia). (ref. ID; 826)
This new species belongs to subgenus Pseudonotholca Marukawa together with N. japonica, having four anterior spines of the lorica instead of bearing six ones in the other species of the genus Notholca Gosse. The species of this subgenus are distinguished from the forms of Notholca s. str. by the disappearance of the two outer anterior spines, though some individuals of this species were observed to have slight indications of these spines. This new species closely resembles N. japonica in general contour, structure of lorica, and dimensions except the posterior appendage of the lorica, which is bifid in this form, thus differing from the latter which has a tapering spine. (ref. ID; 3170)
Type locality
This species seems to be distributed in temperated costal waters (16-17 degrees C) in the Pacific and the Japan Sea. (ref. ID; 3170)
See Notholca striata group. According to the literature N. bipalium seems to be much more common than the two closely related smaller species, as most of the records of a Notholca with mobile lateral spines which can be verified by figures or measurements show this species. The name N. bipalium has almost never been used for this species, however. Records of N. bipalium under other names are:
As N. striata; Carlin (1943); Gillard (1948, 1959); Berzins (1952 (probably), 1960)); Hamelin (1956) (partly); Buchholz & Ruhmann (1956); De Ridder (1957 (partly), 1961, 1967); Rudescu (1960); Amren (1964) (at least partly); Ghilarov (1967) (partly); Thane-Fenchel (1968) (probably partly).
As N. biremis; Ehrenberg (1838); Hudson & Gosse (1889); Levander (1894); Van Oye (1931).
As N. spinifera; Hudson & Gosse (1886); Hood (1895); Lie-Pettersen (1906); Idelson (1926).
N. bipalium has only been found in Europe with certainty, except for a record from New Zealand (Hilgendorf 1898) of a species called N. regularis, which probably is identical with N. bipalium. (ref. ID; 3053)
Marine and brackish water. (ref. ID; 3573)
Measurements
Length of the lorica 185-255; breadth of the lorica 88-90; length of middle anterior spines 12-30; length of lateral anterior spines 8-14 µm. (ref. ID; 3275)
Notholca dongtingensis n. sp. will key out to N. labis Gosse, 1887 following the key by Koste (1978). It differs from N. labis by its large and squarish body shape; anterior lateral spines curved outwards; presence of weak granular ornamentation on the margin of the medventral sinus; protrusible posterior margin of ventral plate, occasionally even projecting beyond posterior margin of lorica. It is also close to N. kozhovi Vassilijewa & Kuticova, 1969 in posterior projection and outwardly curved antero-lateral spines. However, it differs from N. kozhovi by its body shape and much shorter anterior lateral and median spines. (ref. ID; 1978)
Descriptions
Lorica square-oval, smooth without clear longitudinal striation; anterior dorsal margin with 6 short and sharp spines; anterior lateral spines outwardly curved to transversally; median and intermediate spines curving in normal way; anterior ventral margin with six triangular projections and wide median sinus, on the margin of the median sinus with slightly granular ornamentation; protrusible posterior margin of ventral plate, occasionally even projecting beyond posterior margin of lorica; posterior dorsal margin with relatively wide, distally dilating caudal projection; lateral sensory antennas nearly in the beginning of second half of the lorica; trophi malleate; vitellarium large, eight nuclei. (ref. ID; 1978)
Male: Male unknown. (ref. ID; 1978)
Ecology
Cold-stenothermous rotifer. (ref. ID; 1978)
Etymology
The name of the new species is a toponym, derived from the name of the lake, Dongting Lake, Hunan Province, China. (ref. ID; 1978)
Measurements
Total length of lorica 240-250; maximum width 112-115; length of anterior spines (median 8-12, intermediate 8-10, lateral 10-12); caudal projection (length 37-40, maximum width 14-15); rami 22, fulcrum 7; unci 16; manubria 24 µm. (ref. ID; 1978)
The species occurred in the sea of Japan. Four anterior spines. (ref. ID; 1827)
Notholca kostei Chengalath (ref. ID; 826, 829 original paper, 2878)
Descriptions
Lorica more or less spherical; about two-thirds as wide as long, the greatest width slightly behind the middle of the body; laterally compressed. Anterior one-third of lorica with postulations on both dorsal and ventral plates; lateral striations extending almost the entire length of lorica. Dorsal plate with ridges on upper third of body running to middle of anterior spines. Anterior dorsal margin with six spines; medians longest, with broad bases, curved ventrally, pustulated, and with swollen tips; intermediates small, curved ventrally, and swollen at tips. Dorsolateral spines diagnostic, narrow, curved ventrally and in some specimens almost as long as medians, also with swollen tips. Anterior ventral margin fairly well developed intermediate spines. Medians and laterals blunt, forming mound-like projections. Posterior margins of lorica smooth and rounded and in some specimens with a distinct posterior segment. N. kostei resembles N. squamula, mainly because of the round shape of the lorica and the small size. However, it is distinctly different from other Notholca species in having postulations on the lorica, and in the shape of the anterior spines. Anterior spine of N. kostei are relatively longer, with the anterior medians having broad bases, and the anterior laterals being slender and long, unlike N. squamula. Total lorica length of N. kostei (180-210) is larger than for N. squamula (110-190). In lateral view, the lorica of N. kostei is compressed, as is the case of N. squamula. N. kostei is a cold plankton stenotherm, coexists with N. acuminata, N. labis and N. squamula. All these species were found among dense populations of the diatom Melosira. (ref. ID; 829)
Male: Male unknown. (ref. ID; 829)
Etymology
This species is named after Dr. Walter Koste of Quakenbruck, Germany, in recognition of his work in rotifer taxonomy. (ref. ID; 829)
Cosmopolitan in its distribution and displays high polymorphism. Lorica oval, dorsoventrally flattened with 6 anterior spines; median and laterals of same length. Posterior end of lorica with short, broad and blunt process. (ref. ID; 1806)
Measurements
Length of lorica 120-142; breadth of lorica 68-84; length of middle anterior spines 14-18; length of poster processes of lorica 20-22 µm. (ref. ID; 3275)
This species is shown a relatively marked variation, chiefly in the formation of the posterior spine. According to Olofsson N. latistyla is characterized by the fact that the ventral plate projecting beyond the sides and behind the posterior ridge of the dorsal plate and that the posterior spine is broader backwards and increasingly flattened dorsoventrally. However, this description is in certain respects inaccurate. It emerges for Oloffson's Figs.66b and c that the contours on the dorsal and ventral plates have been incorrectly reproduced. The dorsal plate is broader than the ventral one except in the caudal part of the specimens. Thus, the lateral anterior spines belong to the dorsal plate and not, as may be seen in Olofsson's reproductions, to ventral one. Figs.66b and c in his work also illustrate that posterior spine does not become noticeably broader in the caudal part. Instead, a large variation occurs in the formation of the posterior spine. (ref. ID; 3235)
Female: Anterior margin of dorsal plate with 6 spines; anterior margin of ventral plate has 6 folds. Dorsal surface of lorica strongly striated. Body corpulent in lateral view, with a distinct cleft in posterior margin between dorsal and ventral plates. Median dorsal spines recurve ventrally; intermediate dorsal spines longer than lateral dorsal spines. In dorsal view posterior margin of dorsal plate rounded, although frequently gently rounded bulge in posterior extremity of ventral plate exists. (ref. ID; 2773)
Male: Males of N. laurentiae have not been observed. (ref. ID; 2773)
Comments
Notholca laurentiae is morphologically similar to, but distinctly larger than the salt water species N. salina Focke, known from the coastal waters of Europe. Notholca laurentiae has a mean total lorica length of 226 µm as compared to 143 µm (Bjorklund 1972) for N. salina. In Lakes Michigan and Huron no individuals exceeded a total length of 250 µm. However, Nauwerck (1972) recorded N. striata (= laurentiae) from Lake Ontario ranging in total length from 200-285 µm. The median and intermediate dorsal spines are longest in N. laurentiae and N. salina, whereas the dorsal median and lateral spines are longest in N. squamula (and N. michiganensis n. sp.). In lateral view, the body is corpulent in N. laurentiae and flattened in N. squamula (and N. michiganensis n. sp.) Variations in body shape, including indentations or wrinkles on the lorica as well as the presence of a short, rounded posterior extension, may be due in part to the degree of contraction of the lorica after fixation with formalin. Bjorklund (1972) noted similar alterations of body shape in N. salina. The general morphology of the lorica places. N. laurentiae in the N. squamula group of closely related species. Historically, investigators of Great Lakes rotifers have erroneously considered N. laurentiae and N. squamula as a single species mistakenly called N. striata (Muller) (Forbes 1883; Jenning 1896; Ahlstrom 1934, 1936; Chandlel 1940; Davis 1954, 1962). Nauwerck (1972) noted discrepancies between Muller's N. striata, found in the brackish waters of the European coast, and the species found in the Great Lakes, but considered the Great Lakes form identical to N. squamula frigida Jaschnov (= N. frigida). Nauwerck (1972) did, however, clearly distinguish N. striata (= laurentiae) from N. squamula. Stemberger (1974) noted that N. striata of the Great Lakes was sufficiently different from the European species to be considered a new species, based on the fact that the Great Lakes taxon does not possess movable lateral spines and that it is known to occur only in fresh water. Notholca laurentiae, a cold stenotherm, is apparently restricted to the Lauretentian Great Lakes as it has not been recorded in any of the deep water inland lakes of the northern portion of Michigan's lower peninsula. If N. salina were found in North American coastal waters, support would be given for recognizing N. laurentiae as a possible glaciomarine species. (ref. ID; 2773)
Measurements
Mean total length 225.5; mean lorica width 142 µm at its widest point; mean length of median dorsal spines 25; intermedian dorsal spines 9.9; lateral dorsal spines 5.4 µm. (ref. ID; 2773)
Notholca liepetterseni sp. nov. is characterized by its mobile lateral spines on the posterior half of the lorica. In size and shape it is very similar to N. striata, but the mobile spines are, in mean, markedly longer in N. liepetterseni. In the type area (Espegrend) there is no overlapping in spine length. The body length is, in mean, a little greater, and the body breadth relatively somewhat greater in N. liepetterseni than in N. striata. The holotype has all dorsal and the median ventral spines acute. There is some morphological variation between specimens from different habitats and area. (ref. ID; 3053)
Comments
N. liepetterseni or a closely related new species has been found by Hada (1939) in brackish water in Japan, recorded as N. striata var. biremis. His specimen has a length and mobile lateral spines like the typical Espegrend specimens of N. liepetterseni, while the relative length of the dorsal spines was as typical for the Hudson River specimens. The body breadth was relatively still smaller than on the latter specimens, but this may partly be caused by a rather great extension of the lorica posteriorly. (ref. ID; 3053)
Female: Anterior margin of dorsal plate with 6 spines, anterior margin of ventral plate has 6 folds. Dorsal surface of lorica distinctly striated; body somewhat compressed in lateral view, continuous and rounded in the posterior extremity. Well-rounded dorsal and ventral plates give body a circular appearance. Median dorsal spines recurved ventrally; lateral spines about twice as long as intermediate dorsals. (ref. ID; 2773)
Comments
Notholca michiganensis, a clod planktonic stenotherm, shows strong morphological resemblance to N. frigida of Europe, which is considered as a possible polyploid of N. squamula (Ruttner-Kolisko 1974). Total lorica length of N. michiganensis (180-220 µm) is considerably smaller than for N. frigida (300-400 µm) (ibid.). Variation in body shape of N. michiganesis may be due partly to the state of contraction of the lorica after fixation with formalin. No wrinkles or indentations on the lorica were ever noted. The ventral and lateral aspects of the lorica of N. michiganensis are notably similar to N. squamular. In lakes where N. squamula and N. michiganensis are notably similar to N. squamula. In lakes where N. squamula and N. michiganensis coexist, individuals of intermediate size were not found. However, I observed a large littoral form of N. squamula (lorica length 150-195 µm) which, although somewhat larger, agrees in both shape and habitat with the form found by Carlin (1943) and discussed by Amren (1964). This form was found in samples at inshore Lake Erie stations near Lorain, Ohio, and in Lake Michigan near Two Rivers, Wisconsin, during spring 1976. The relative lengths of the median, intermediate, and lateral dorsal spines determined for 15 specimens were 19.5, 7.8 and 17.4 µm, respectively. The lorica of this large form mean length 173 µm, width 133 µm) had wrinkles and indentations which commonly occur on the smaller N. squamula form. The lorica of N. michiganensis is more constricted immediately below the anterior spines than the large N. squamula form, which imparts a more circular appearance to the body. In addition, the relative lengths of the anterior spines differ. The general morphology of the lorica places N. michiganensis in the N. squamula group of closely related species. (ref. ID; 2773)
Measurements
Mean total lorica length 199.5; lorica width 144.9 at widest point; median dorsal spines length 28.5; lateral dorsal spines 19.7; intermediate dorsals 9.6 µm. (ref. ID; 2773)
See N. squamula-group. (ref. ID; 3053)
The dorsal surface, which in British specimens is usually furrowed with numerous longitudinal striae, was much smoother and in some cases these were scarcely visible, except immediately below the anterodorsal spines. (ref. ID; 3334)
Male: It was approximately one-third the size of the female at 50 µm and had a rudimentary lorica complete with anterodorsal spines. In common with most male rotifers, it lacks a digestive system. No protrusible foot or penis was seen. (ref. ID; 3334)
Comments
N. salina has only recently been recognized as a separate species, Originally, it was identified as N. squamula, a species with a world-wide distribution that can tolerate a wide range of temperatures and salinities (de Ridder 1972; Ruttner-Kolisko 1974). However, Focke (1961) separated the freshwater and brackish specimens into subspecies (N. s. mulleri and N. s. salina) on morphological grounds. Subsequently, Bjorklund (1972) has considered them as separate species. (ref. ID; 3334)
Measurements
It is a medium-sized rotifer with a lorica length of 175 µm and width of 95 µm, but it is very flexible, being elongated when the head is fully extended and considerably widened when the animal is fully retracted. (ref. ID; 3334)
Cosmopolitan in its distribution and displays high polymorphism. This species is euryhaline. (ref. ID; 680)
Comments
Carlin (1943) believes himself to have found two separate forms of N. squamula, viz, a small form (body length 120-130 µm) with long median anterior spines, presumed to be characteristic of the plankton of the lakes, and a bigger form (130-180 µm) with short spines, typical of the plankton of the ponds and the littoral zones of the lakes. Focke (1961) distinguishes between the three limnic forms of N. squamula, viz., a small lake form with long median anterior spines, a relatively large littoral form with short spines, and a so-called normal form that takes an intermediate position between the two first-mentioned ones and, apparently, occurs in lakes as well as ponds. Focke has, nevertheless, found transitional forms between the three main types, and has therefore sometimes encountered difficulties in determining the exact classification of a specimen. (ref. ID; 3235)
Measurements
Total length 100-125; breadth 70-80 µm. (ref. ID; 1402)
Length of lorica 112-132; width of lorica 83-103; length of middle anterior spines 10-13; length of lateral anterior spines 10-17 µm. (ref. ID; 3275)
Carlin (1943) described that a posterior spine or prolongation is usually lacking. Where it exists, it is rather rounded. A lateral incision at both sides in the lower middle of the lorica appears frequently but the appendages. But this species found that the lorica is often strongly striated and also often shows a wrinkled outline. There is no doubt that this species is identical with N. striata (O.F. Muller) in the older Great Lakes literature (ref. ID; 1402)
Lorica ovate or more elongate, rounded behind. With rather strong striae on dorsal plate. Two lateral mobile setae on the posterior part of lorica, rather stout but short. Marine species, especially in the littoral zone. Planktonic close to the bottom. (ref. ID; 4594)
Comments
Most earlier authors have considered N. striata a synonym of N. squamula, and very few authors have distinguished between N. striata and the larger N. bipalium. Focke (1961), after a detailed study, has stated that they are two species. The two species often occurred together, but I never found intermediate forms. Ghilarov (1967) noted that two populations of N. striata with different proportions occurred in the same rock-pool in arctic Russia, his figures show the two species N. striata and N. bipalium. De Ridder (1957) found many unusually small specimens of what she called N. biremis (Ehrenberg) together with specimens of normal length in December, the first month in which the species occurred in the same samples. She supposed that the small specimens represented the first generation after a resting period, but they seem in fact to have been N. striata. I found N. striata itself to vary somewhat in the size and shape of the lorica. In summer the specimens were smaller than in winter, and some specimens, found mostly in a marine environment, had much longer lateral spines than those found typically at low salinities. There was no overlapping between the two types, although they were sometimes found together. On the south coast of Finland I have found a few intermediate specimens together with the low salinity form, but the typical marine form appeared to be absent. (ref. ID; 3573)
Measurements
Total length 200-285; breadth 100-150-190 µm. The average length/breadth ratio is close to 1:1.5. (ref. ID; 1402)
Length 234; width 168 µm. (ref. ID; 1489)
Length of the lorica 115-118; width of the lorica 68-75; length of middle anterior spines 10; length of lateral anterior spines 15 µm. (ref. ID; 3275)
Total length 190-250 µm. (ref. ID; 4594)
According to Skorikow's description, the three long, thin and curved appendages, two lateral and one posterior, are movable, in the same way as are the two small lateral spines in Notholca spinifera; but farther on the author states that he has not seen the posterior spine move, so there appears to be uncertainty as to whether the posterior appendage is really capable of movement, which I much doubt. By means of the spines the animal is said to be capable of jerky forward movements in the manner of a Triarthra. The lorica is very thin, resembling in this respect the marine plankton forms; it is oval in shape, with a high and rounded back, and has six fine longitudinal markings. The occipital edge is armed with six spines; the ventral plate is flat, and gapes posteriorly. (ref. ID; 3216)
Type locality
The River Neva near St. Petersburg, in April 1903. (ref. ID; 3216)
Measurements
Size of lorica, exclusive of spine, 1/120 in. (212 µm). (ref. ID; 3216)
The dorsal plate of the lorica (190 µm) has handle-like postero-dorsal elongation. Both lorica plates appear to be covered in discontinuous striae when viewed at low power. Closer examination shows that the striae are, in fact, the edges of longitudinal rows of cup-like depressions. In some places, especially below the anterio-median spines, these hollows appear to overlap or merge into each other in a crater-like fashion. Viewed edge-on, the rows of cuplike depressions have the appearance of a serrated surface. The lorica crumples very easily in preserved specimens, which further accentuates the appearance of false striae. (ref. ID; 3334)
Egg: Eggs are brown and circular to oval in shape (75 µm by 60 µm). (ref. ID; 3334)
Male: Males were not seen. (ref. ID; 3334)
Comments
In its various locations, N. walterkostei showed considerable variation in both size and shape. The specimens from South Georgia were smaller (length of lorica 160 µm, width 56 µm), though in all other respects were identical with the Signy specimens. The specimens from Ablation Point, Alexander Island, though similar in size, had an even more pronounced caudal process and longer anterior spines. N. walterkostei is obviously closely related to N. verae, fist described by Kutikova (1958) from plankton collected in the Bunger Hills and subsequently reported from there by Korotkevich (1958) and Kutikova (1958), and from Deep Lake Tarn in the Vestfold Hills (Everitt 1981). (ref. ID; 3334)
Type locality
N. walterkostei was first described by Paggi (1982) from the South Shetland Islands. (ref. ID; 3334)
Measurements
It is a medium-sized rotifer with a total length of 200 µm and greatest width of 75 µm. (ref. ID; 3334)
The posterocaudal process and the anterodorsal spines are considerably reduced when compared with that species. The cup-like depressions are restricted to the area just below the frontal spines and in this respect it shows an affinity with N. foliacea. (ref. ID; 3334)
Comments
N. walterkostei reducta is of considerable interest, not only because of its restricted distribution on Signy, but because it appears to be intermediate between N. verae and N. walterkostei. (ref. ID; 3334)
Type locality
This new subspecies was found only in Tioga Lake and in the lake at Cape Hansen, Coronation Island. (ref. ID; 3334)
Measurements
While this species is somewhat smaller than the sensu stricto N. walterkostei from the South Shetlands, Signy Island and Alexander Island, it is similar in size to those from South Georgia with a lorica length of 160 µm and maximum width of 65 µm. (ref. ID; 3334)
