Soft-loricate, elongate rotifers. Foot with three pseudosegments, strongly muscular. Toes elongate, with basal muscles.
Female: Body loricate, divided into head, trunk and foot. Head with ventral and dorsal pair of lateral lobes, presenting dorso-ventral fissure from trochus to dorsal antenna. Corona apical field with undifferentiated, motile cilia; ventral trochus with buccal field of stiff setae encircling mouth, and some cilia ventro-laterally. Mouth supported ventrally by stiff, toothed membrane, dorsally by epipharynx. Unci projecting through mouth. Buccal cavity with epipharyngeal teeth, setae and antenna. Trunk covered by complete, relatively soft lorica, with weak, longitudinal striae ventrally. Two pairs of antero-ventral to postero-dorsal, sublongitudinal folds. Aperture to the lateral antennae approximately halfway between sublongitudinal folds. Eyes absent, mastax with apical red spot. Vitellarium with eight nuclei. Foot inserted ventrally, with three pseudosegments. Food muscles transversally striated, conspicuous. First foot pseudosegment short. Second elongate, with 1 pair of lateral, fan-shaped and four pairs of semi-longitudinal muscles. Third foot pseudosegment the longest, with pair of strong longitudinal muscles dorsally. A papilla or pore of unknown function dorsally on joint between third foot pseudosegment and toes. Two elongate, equal toes, having relatively short basal muscle. Trophi modified virgate, symmetrical. Fulcrum elongate, with midventral crest and, occasionally, basal plate. Rami with varying antero-ventral teeth. Suprarami strong. Alulae, if present, characteristic. Each bulla ramus is acutely pointed, elongate basal apophysis, with subapical accessory tooth. Fan-shaped ventral lamellae preceding the basal apophysis. Manubria S-shaped, proximal part short, transverse median part longer, with anterior, occasionally posterior lamellae and ventro-posterior lobe. Distal part mostly elongate, rod-shaped. Unci with single major tooth. Epipharynx when present weakly sclerotized, consisting of toothed, horseshoe-shaped anterior part, and pair of elongate, dorsal projections. (ref. ID; 2985)
ref. ID; 3334
In this genus, the foot and toes are longer than the lorica. The foot and toes are highly mobile with strong striated muscles running through them. The lorica, which is thin and flexible, is cylindrical in shape. The corona is simple. The mastax has modified virgate trophi. (ref. ID; 3334)
A relatively small Scaridium, though of stouter build than S. longicaudum. Uncus not dilated at articulation with ramus. Posterior tip of ramus very acutely pointed. Basal part narrower and less swollen than in S. longicaudum. (ref. ID; 2825)
Fulcrum with high midventral crest, basal plate well developed. Rami teeth large. Alulae rounded. Basal part of unci triangular. Uncus tooth robust, strongly curved, acutely pointed, with subapical accessory tooth. Manubrium relatively narrow and transversally divided proximally, ventral margin convex. Ventroposterior projection small, triangular. No posterior lamella, epipharynx with subequal teeth. (ref. ID; 2985)
The two-segmented foot is long and bears even longer toes that enable this species to swim with a flicking movement. There is a single, red eyespot. (ref. ID; 3334)
Egg: Only on large, brown, circular/oval egg, covered in papillae. (ref. ID; 3334)
Comments
A small, though strongly built species. The morphometrical characteristics are clearly lower than these of S. longicaudum from the same habitat. The ratio head+body length/length of toes is seen to be consistently lower in S. bostjani. No intermediates are observed. Considerable scatter occurs here in head+body length, doubtlessly due to a variable degree of contraction, but no noteworthy variability is observed in the length of the toes. Also should it be stressed that the variability tends to widen the gap with S. bostjani, rather than narrowing it. The fundamental structure is identical to that of S. longicaudum. Differences in details are most obvious in the unci and manubria. Manubrium: bais elongate, posterior tip triangular: anterior tip, articulating with unci, narrow, tapering towards apex. Posterior projection swollen towards its top, then abruptly narrowed, ending in along, thin, very sharply pointed filament. Uncus curved, ending in a bident tooth, not swollen at its articulation with manubria. (ref. ID; 2825)
The Antarctic record of S. bostjani by Dartnall & Hollowday (1985) is a misindentified S. longicaudum; a Zaire record of S. cf. bostjani by De Smet (1990) undoubtedly concerns S. elegans. (ref. ID; 2985)
S. bostjani differs from S. longicaudum in the form of the manubrium. In general shape, the manubria of these species are similar but S. bostjani has a characteristic narrow neck to the upper part. The Signy Island specimens show greater variation in size than the Nepalese specimens of Dames & Dumont (1974), While most of the Signy specimens were slightly smaller than, or approximately equal in size to those of Dames & Dumont, a few were considerably longer and almost came within the lower size range of S. longicaudum. S. bostjani and more comparable with S. longicaudum. (ref. ID; 3334)
Type locality
Daems & Dumont (1974) have described a new species, S. bostjani, from Kathmandu-Tal, in Nepal. (ref. ID; 3334)
Measurements
Total length 281-288; head + body length 84-90; first and second foot joint length 31-33; third foot joint 60-63; toes length 104-106; mastax length 40 µm. (ref. ID; 2825)
Total length 304-373; body length 103-142; trunk length 67-101; second foot pseudosegment 31-41; third foot pseudosegment 70-83; toe length 106-131; fulcrum length 22-33 µm. (ref. ID; 2985)
It is a medium-sized rotifer, up to 352 µm long. (ref. ID; 3334)
Scaridium elegans Segers & De Meester, 1994 (ref. ID; 1324 original paper, 2017, 2985, 7846)
Synonym
Scaridium cf. bostjani after De Smet, 1989 (ref. ID; 2017, 2985)
Descriptions
Parthenogenetic female: Head rounded, corona antero-ventral. Trunk elongate, with two pairs of sublongitudinal lateral folds. Lateral antennae medial. Vitellarium with eight nuclei. Ventro-posterior foot elongate, strongly muscular. First foot peudosegment short, second about three times as long as high, third nearly ten times as long as high. Two strongly elongate, parallel-sided toes present. Fulcrum elongate, basal plate well-developed, ventro-median crest strong. Rami with large, elongate and pointed allulae and supraunci, supraramus well-developed. Unci nearly straight. pointed, with small median projection. Manubria plate-shaped, with acute ventral and dorsal posterior process. (ref. ID; 1324)
Male: Male unknown. (ref. ID; 1324)
Animal relatively small, second foot pseudosegment and toes long. Trophi small. Midventral crest of fulcrum low, basal plate present. Rami teeth small. Alulae elongate, acutely pointed. Basal apophysis needle-like. Unci elongate, slender, small projection medially, tooth needle-like, straight. Manubrium small, proximally narrow, ventral margin nearly straight. Ventroposterior projection triangular, sharp. No posterior lamella. Medial and distal parts not clearly separated. No epipharynx seen. (ref. ID; 2985)
Comments
Scardium elegans can be distinguished from the two other species in the genus by the structure of its trophi. In S. elegans, the fulcrum is relatively short, the allulae long and pointed. In S. longicaudum (O.F. Muller, 1786) and S. bostjani (Daems & Dumont), it is short and rounded. The manubria are characteristically shaped in all species, and appear to be species-specific. The third foot pseudosegment of S. elegans is relatively longer than in both other species. (ref. ID; 1324)
Etymology
The species name- elegans is an adjective, referring to the general shape of the species, and, in fact, of the genus. (ref. ID; 1324)
Measurements
Total length 289-400; body length 72-101; first foot pseudosegment 5-10; second foot pseudosegment 21-34; third foot pseudosegment 70-81 µm; toe length 113-139; trophi length 30-32; fulcrum length 15-17; uncus length 13-17; manubrium 17-18 µm. (ref. ID; 1324)
Total length 286-340; body length 72-101; trunk length 54-82; second foot pseudosegment 21-34; third foot pseudosegment 70-81; toe length 113-142; fulcrum length 15-17 µm. (ref. ID; 2985)
Animals large, second foot pseudosegment and toes relatively long. Head relatively large, trunk mostly with distinct fold antero-ventrally. Ventral pair of head lobes with small notch. Fulcrum with low midventral crest, basal plate extending anteriad. Rami teeth small. Alulae hook shaped, pointed to frontally and medially. Basal part of unci triangular. Uncus tooth large, curved, acutely pointed, with accessory tooth. Manubrium narrow proximally. Ventroposterior projection small, rounded. Anterior lamella well developed, posterior, lamella large, weak. Terminal rod-shaped part especially elongate, connected with posterior lamella. Epipharynx with a group of long posterior and short anterior teeth. (ref. ID; 2985)
Etymology
The name grandis (adj.) is Latin for 'large, voluminous', and refers to the species' large size. (ref. ID; 2985)
Type locality
Lake Akika, Imo State, Nigeria. (ref. ID; 2985)
Measurements
Total length 430-528; body length 131-183; trunk length 85-129; second foot pseudosegment 45-51; third foot pseudosegment 104-134; toe length 165-204; fulcrum length 35-41 µm. (ref. ID; 2985)
Lorica thin, more or less cylindrical. Foot three-segmented, striated muscle strands prominently visible in foot segments. Toes very long. (ref. ID; 1804)
Lorica more or less cylindrical and very thin and transparent. Body comparatively small with a long foot. Two segment foot. The toes are very long. (ref. ID; 2715)
Animal large, second foot pseudosegment and toes relatively short. Fulcrum with high midventral crest, basal plate well developed. Rami teeth large. Alulae rounded. Basal part of unci triangular. Uncus tooth robust, strongly curved, acutely pointed, with subapical accessory tooth. Manubrium relatively broad and transversely divided proximally, ventral margin nearly straight. Ventroposterior projection large, rounded, exceptionally asymmetrical. No posterior lamella. Epipharynx with equal, small teeth. (ref. ID; 2985)
Male: Male present. (ref. ID; 2985)
Comments
The identity of the insufficiently characterized S. longicaudum maculatum Bergendal, 1892 (originally described as a 'form', trinomen by Harring (1913) and subsequent authors) can only be inferred, as its diagnosis: "...einer Scaridiumform, welche sehr eigenthumliche hellgelbe Flecken im Kopfe besassen" (Bergendal, 1892) does not permit identification. Harring's (1913) synonymy of the taxon with S. longicaudum, on the other hand, is only substantiated by the general statement that "Names proposed for units of less than specific rank have as a rule been thrown into synonymy". Consequently, the taxon cannot be listed as a synonym, but is a 'species' inquirenda. An Antarctic record of S. bostjani by Dartnall & Hollowday (1985) concerns misidentified S. longicaudum, as follows from the examination of relevant material deposited in the British Museum (Natural History). (ref. ID; 2985)
Measurements
The total length 350 and 395; toe length 123 and 135 µm. (ref. ID; 1450)
Total length of lorica 125; foot length 70; toes length 160 µm. (ref. ID; 1804)
Toe length 117 µm. (ref. ID; 2683)
Total length 321; length of body 96; foot 90; toe 132 µm. (ref. ID; 2715)
Total length 374-395; head+body length 120-124; first and second foot joint length 44; third foot joint 74-81; toes length 136-146; mastax length 48 µm. (ref. ID; 2825)
Total length 358-428; body length 125-168; trunk length 91-134; second foot pseudosegment 34-44; third foot pseudosegment 72-90; toe 116-149; fulcrum 27-34 µm. (ref. ID; 2985)
Total length 344-360; body 120 long; anterior extremity 40-65 high; middle part 76-78 high; caudal projection or protuberance 28-36; foot 1st 42-44, 2nd 60-68; toes 124-128 µm. (ref. ID; 3083)
Total length 355-415; length of toes 130-150; length of fist foot joint 45-55; length of second foot joint 65-80 µm. (ref. ID; 3275)
