Lorica composed of one rigid piece, body not laterally compressed. Surface of lorica marked with ridges. Lorica open along the midventral line. Corona with frontal palps. Foot annulated. Mastax virgate and adapted for prehension. (ref. ID; 1663)
ref. ID; 1923
Corona without prominent processes lateral to mouth. Dorsal antenna on lorica. Lorica heavily marked with ridges and grooves or with areolations. (ref. ID; 1923)
ref. ID; 4595
Lorica firm; often open along the midventral line. Corona with frontal palps. Foot long and annulated. (ref. ID; 4595)
Ploesoma africana Wulfert, 1965 (ref. ID; 2135 original paper, 3514)
This species has a frothy-appearing epidermis which gives the thin, flexible lorica an areolated appearance. Wiszniewski (1953) removes this species to the monotypic genus Bipalpus Wierzejski and Zacharias 1893. (ref. ID; 1923)
Often with foam-like structure of the hypodermis. Without open midventral line. Freshwater species, found in estuaries. (ref. ID; 4595)
The three anterior spines were relatively short, the middle one being curved downwards. Von Hofsten (1923, Fig.9) has a drawing of a form from the Swedish fjell with considerably longer spines under the name of "P. triacanthum (Bergend.)", which is a synonym of P. lynceus (see Voigt 1956-57, p.405). (ref. ID; 1450)
The present variety has some intermediate features among P. lynceus, P. lenticulare and P. truncatum. The antero-ventral projection, which is regarded as the most important character to identify Ploesoma- species, is not truncated, but provided with one spines as lenticulare though indistinct. The present animal has no such cleft as found in lenticulare on the middle of the dorsum or just behind the dorsal antenna. The general shape of the body is like an egg-apple without any marked indention of the lorica. The foot is comparatively long, the toes are large 28 µm in length. At the base of the foot there is one markedly large sheath-like segment. (ref. ID; 3084)
Comments
As the genus Ploesoma has insufficiently been studied, we know nothing about the range of variation or stability of the anteroventral spine. The present author considers that P. lynceus (Ehrenberg, 1834) and P. triacanthum (Bergendal, 1892) are valid species, and the present species may be received as a new variety under the former species. (ref. ID; 3084)
This variety is distinguished from the typical lynceus (e.g. lynceus lynceus) in the following points, 1) of two spines sharply developed at the anteroventral extremity of the lorica, the first is more stout than the second, 2) the whole edge of the dorsal surface is smooth and not so indented as in lynceus lynceus, 3) the pectoral edge is round and never quadrilateral, and 4) the striations on the lateral lorica are not limited to the dorsal side only. (ref. ID; 3084)
Lorica rigid, oval, noticeably narrowing distally (specimens with ovary less narrowed), its central part being widest. Frontal dorsal margin of lorica hangs over head as a wide plate without spines and with three round lobes; middle lobe directed downwards, lateral ones reaching far ahead had aside. On sides of lorica 5 clearly district lateral ridges with margins armed with spines. Several longitudinal ridges on dorsal part: 3 pairs of medial ridges are connected with 3 crosswise ridges. On ventral side there is a large sulcus with a big goblet-like cut on its frontal margin. On foot sides, from the margin of sulcus wing-like crosswise ridges branch off and reach powerful lateral longitudinal ridges. The whole lorica is covered with thick plaque-like papillae which become united on the ridge margins and form fine spines. Eye red. As compared with the length of lorica, its foot is relatively short and never extends over the posterior margin (even when stretched out backwards). It is usually much shorter than lorica. Foot, as usually, ringed on the basis. Its distal part is jointed and has two oblong toes. (ref. ID; 3183)
Comments
The species Ploesoma peipsiense differs from all the seven species known to the authors: P. truncatum (Levander, 1894), P. lenticulare (Herrick, 1885), P. tricanthum (Bergendal, 1892), P. lynceus lynceus (Ehrenberg, 1834), P. lynceus lenticularis (Sudzuki, 1960), P. lynceus rotundus (Sudzuki, 1960), P. murrayi (Wulfert, 1961), P. multispinata (Wulfert, 1965) and P. africana (Wulfert, 1965). The new taxon differs from the species P. truncatum by stronger papillae of its lorica (those of P. truncatum are either absent or very small), comparatively slender and longer lorica, the posterior margin of which always reaches farther than the backward stretched foot and by a stronger forward protrusion of lateral lobes of the head plate. The species differs from P. lenticulare by the form of its lorica and placing of ridges, from P. tricanthum and P. murrayi by the absence of sharp frontal dorsal spines, from P. africana by the structure of the frontal margin of its lorica and the placing of ridges. The sculpture of the lorica of the new taxon is slightly similar to that of P. multispina, but the frontal margin and ridges of the latter species are of quite a different structure and the surface of its lorica is covered with still more spines. (ref. ID; 3183)
Measurements
Total length 172-176; biggest width 94-103; length of the most distal joint of foot 20; length of toe 21 µm. (ref. ID; 3183)
The anterior end of the head is separated into three triangular processes of which the central one is the longest. In general, this portion bends downward as a shield-like head. (ref. ID; 3063)
The body is ovoid in shape resembling Testudinella; its greatest width is about one third of the entire body length. The integument bears small spin lets developed mainly on the posterior part of the body. The head is convex anteriorly, its width is less than 1/2 of the greatest width of the body. At the apical region of the head there is found a tuft of rather long cilia, at the both sides found auricle-like area. The abdomen is perfectly ovoid in shape, being widest at the level of about 1/3 from the tail, and from there it tapers suddenly toward the tail extremity. There is a double knobbed papilla with a tuft of a short seta, each of upper projection has gland-like structure. The foot three-jointed, hence the name trisegmenta. The toes are more or less stout at the base, pointed terminally: their length is about 12 µm and little less than the length of the foot. The dorsal antenna is remarkable, consisting of a tuft of short cilia on the knob-like projection. It is located in the middle of the head when fully stretched, but usually neck. The mastax is of a malleate type, fulcrum is short, tapering to the posterior end. The lateral antennae are asymmetrically situated at about 1/3 of the body length from the tail, consisting of one strong seta on the projection. The oesophagus is pretty long, 3 µm in diameter, 20 µm in length. One eye present. Both protonephridia and gastric glands are normal. At the base of the foot there are found a pair of strong seta. (ref. ID; 3084)
This species is in several respects different from European descriptions but there is no doubt that it is identical with P. truncata. The species is considerably smaller than recorded in the literature. The smallest individuals, those having just left the egg, are only 60 µm long. After that, a stretching growth takes place to a degree which is unusual in rotifers: at a length of 130 µm the animals are "adult" and are found carrying eggs. Average size for "adult" is 150 µm. The biggest animal measured was 166 µm long. This means, the biggest animals are just above the lower size limit reported for the species by Voigt (1957) and still below the smallest size given by Rylov (1935). The upper limit given in the literature is around 300 µm. Foot and toe length do not, or only very slightly, change after birth. The length of the foot is 65-75 µm, where of the toe is 25 µm. The relationship foot length/body length thus changes with age from close to 1:1 to around 1:2.5. The eye is dark violet to black as recorded for other Ploesoma species but not red as recorded for P. truncata. Lorica sculpture sometimes fit the description of that of P. truncata but sometimes is more like that of P. lynceus (Ehrenberg) with respect to the structure of the central triangular field. (ref. ID; 1402)
Lorica firm, with many ridges placed longitudinally and also across the dorsal side. Open along midventral line. Lorica rounded in front. Freshwater species, in estuaries and brackish bays. (ref. ID; 4595)
Measurements
Length of body 123-132; width of body 90-105; length of foot (extended) 70-75 µm. (ref. ID; 3275)
Length 150-300 µm. (ref. ID; 4595)
The head-plate of the shell is dorsally nearly straight with small indentations, which looks like a broad tongue if the caudal part is lifted. There are transverse ridges and borders behind the dorsal antenna. The surface of the shell has many longitudinal ridges, which dorsally bound a characteristics triangle. The foot is partially annular in the upper reach. (ref. ID; 2834)
Measurements
Body length 120-160; foot length 70-80; toe length 25-32 µm. (ref. ID; 2834)
