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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Tasserkidrilus

Tasserkidrilus Holmquist, 1985 (ref. ID; 7854, 7924)

Family Tubificidae (ref. ID; 6651)

ref. ID; 7924

This genus was created for the species Tubifex americanus Brinkhurst and Cook, 1966, T. kessleri Hrabe, 1962, T. hrabei Sokolskaja, 1973, and T. montanus Kowalewski, 1919, which were transferred from Tubifex Lamarck, 1816, to the new genus as a result of the revision by Holmquist (1985). Timm (1989), after finding Tubifex acapillatus Finogenova, 1972, a species originally described from the Caspian Sea (Finogenova, 1972) and also found in Lake Baikal (Hrabe, 1982), reexamined the type material for this species and the closely related Baikal taxa Tubifex kessleri baicalensis Semernoy, 1982, T. kessleri variabilis Semernoy, 1982, and T. mirandus Snimschikova, 1982. As result, the genus Tasserkidrilus was revised and its diagnosis expanded and clarified. According to the diagnosis proposed by Holmquist (1985) and Timm (1989), the genus Tasserkidrilus is characterized by the presence of bifid setae, sometimes together with capilliform and fan setae, the absence of genital setae, and of ventral setae of segment XI in sexually mature individuals; the vas deferens is at least two times longer than the atrium, consists of 2-3 parts differing in thickness, partially or entirely ciliated, open into the atrium apically. The atrium is tubular or spindle-shaped, with a large, lobular prostate gland opening into the middle or distal part of the atrium; the vas efferens is very short or absent. The penis is in a penial sheath of a specific shape (funnel-shaped base, tubular asymmetrical continuation, distal opening obliquely directed). The ampulla of the spermtatheca is larger or compact, spherical, more often bichambered, the thick-walled duct opens in the lateral line or below. Spermatozeugmata present. Timm (1989) included six known species in the genus Tasserkidrilus: the type species Tasserkidrilus americanus (Brinkhurst and Cook, 1966), occurring in the Great Lakes and certain other lakes of North America; T. acapillatus (Finogenova, 1972) from the Caspian Sea, Lake Baikal, and Angara River and Bratsk Reservoir of Chudskoye Lake; T. baicalensis (Semernoy, 1982) from Lake Baikal; T. hrabei (Sokolskaja, 1973) from the waters of Kamchatka and the Koryak Highlands; T. kessleri (Hrabe, 1962), for Lake Onega; and T. mirandus (Snimschikova, 1982) from Lake Baikal. T. kessleri variabilis is the junior synonym of T. acapillatus. Holmquist (1985) placed Tubifex montanus in the genus Tasserkidrilus, but Timm did not believe it belonged in that genus because its vas deferens was uniform throughout and its atrium is pear-shaped, as in Tubifex tubifex (Muller, 1774), and it has a simple (in species of Ilyodrilus Eisen, 1873) penial sheath. We support the substantiated decision of Timm to exclude T. montanus from the genus Tasserkidrilus, and propose including three new species in it from Lake Baikal which, based on the main characters of the internal structure entirely correspond to the diagnosis of the genus Tasserkidrilus. (ref. ID; 7924)

Type species

Tasserkidrilus americanus (Brinkhurst and Cook, 1966) (ref. ID; 7924)
  1. Tasserkidrilus acapillatus (Finogenova, 1972) (ref. ID; 6660)
    Syn; Tubifex acapillatus Finogenova, 1972 (ref. ID; 7924)
  2. Tasserkidrilus americanus (Br., 1966) (ref. ID; 6651)
    Syn; Tubifex americanus Brinkhurst and Cook, 1966 (ref. ID; 7924)
  3. Tasserkidrilus harmani (Loden, 1979) (ref. ID; 6651)
  4. Tasserkidrilus heterodontus Snimschikova & Akinschina, 1993 (ref. ID; 7924 original paper)
  5. Tasserkidrilus hrabei (Sokolskaja, 1973) (ref. ID; 6651, 7924)
    Syn; Tubifex hrabei Sokolskaja, 1973 (ref. ID; 7924)
  6. Tasserkidrilus mirandus Snimschikova, 1982 (ref. ID; 7924)
    Syn; Tubifex mirandus Snimschikova, 1982 (ref. ID; 7924)
  7. Tasserkidrilus rectitubifer Snimschikova & Akinschina, 1993 (ref. ID; 7924 original paper)
  8. Tasserkidrilus timmi Snimschikova & Akinschina, 1993 (ref. ID; 7924 original paper)

Tasserkidrilus heterodontus Snimschikova & Akinschina, 1993 (ref. ID; 7924 original paper)

Diagnosis

Based on the structure of the genital organs, T. heterodontus is very similar to T. timmi and it is difficult to define distinctive features. In comparison, the spermatheca in T. timmi is larger, the vas deferens wider in the distal part, and the penial sheath has a deeper funnel-shaped base. But these differences may be variable and not clearly species-specific. There are sharp differences in the structure of the setal apparatus between the two, obviously closely related, species. The development of the setae have followed diffferent paths: in T. timmi, their number per bundles has declined (to two), but size has increased, the distal tooth is more developed and the proximal one, being squeezed out by the former, has become smaller, but has not entirely disppeared. In T. heterodontus, on the contrary, the distal tooth has evolved to a smaller size and the proximal one remains thicker; in addition, both teeth have become smaller to the point of disappearing on the inner setae of the anterior segments. On the other anteclitellar segments, the teeth of the inner setae of the bundle have become smaller and the outer setae have remained with long teeth. The number of setae per bundle remained normal for tubificids. (ref. ID; 7924)

Descriptions

Body length 8-10 mm, greatest diameter in region of clitellum 320-480 µm, number of segments 45-50. Coloration of specimens fixed in formalin light yellow, integuemnt weakly translucent, plicate. Prostomium small, caplike, prolobous, a little wider than long at the base. Segments II-V compressed, biannulate with narrower anterior furrow. Setal bundles located on posterior, wider, furrow. Segments VI-VIII more pronounced, multiannulate, in succeeding segments annularity weakens, entirely disappears past clitellum. Intersegmental furrows of anterior five segments rather deep, successive ones difficult to discern. Blood circulatory system well developed, blood vessels in each segment from dense networks. Chloragogen tissue begins in middle of segment VI. Setal tubercles very small, do not rise above body surface or just barely. Dorsal and ventral setae all of one form, bifid, on anterior segments (II-V) with short, rudimentary teeth abraded at the ends, or of equal length or with a longer and thicker proximal tooth, sometimes on segments II-III the teeth disappear completely and the seta become single-tipped, with blunt, irregular ends. On segments VI-VIII, the setal teeth are of medium length; on the postclitellar segments, they are again short. The nodulus strongly shifted tiward distal nargin, located at 7/10 of the length of the seta. On segments II-III, there are 4(3) setae per bundle 33-40 µm long, on V-VII there are 5 setae per bundle 56-65 µm long, on VII-X there are 4(3) setae per bundle 50-54 µm long, past the clitellum there are 2-3 setae per bundle 42-45 µm long, that is, the length of the setae, their number per bundle, and the length of the teeth increase gradually from segment II to segment VII. In addition, the teeth of the setae on anteclitellar segments have a different length in the same bundle, and the length of the teeth increases from the inner (median) setae of the bundle toward the outer (lateral) ones: on segments II-III the inner setae have the shortest rudiments of teeth or the teeth disappear completely and the first, second (third) setae become single-tipped and the fourth (lateral) is always bifid; on segments IV-VII, the inner setae have short teeth and most often teeth of equal length, on the medial setae the teeth are longer, and usually the proximal tooth is two times thicker than the distal one, and the teeth are longest, or of different length or with a longer distal tooth on the extreme outer setae. All setae are identical on the postclitellar segments, their teeth short, equal in length, but the proximal one is usually two times thicker than the distal one. In sexually mature specimens, the ventral setae of segment IX are absent, and there are no modified genital setae. Clitellum ring-shaped, poorly defined, rises slightly, takes up last quarter of segment X, segment XI entirely, and half of XII. Spermathecal openings on segment X lateral to line of ventral setae, male gonopore on segment XI at place of absent ventral setae. Reproductive organs located on segments typical of the Tubificidae. Seminal funnels medium-sized, vas deferens in proximal part ciliated, in distal part not ciliated, enters atrium apically. Length of the vas deferens more than 100 µm, diameter in proximal third 24 µm, in middle and distal thirds 32 µm. Atrium cylindrical, distally narrows and changes via the short vas efferens into slender, long penis provided with penial sheath and placed in large penial sac. Penial sheath has funnel-shaped base, tubular, slightly arched and somewhat expanded in the middle continuation that gradually narrows toward both ends and is again weakly expanded distally, with a regularly cut margin, the opening of the tube is directed down and slightly obliquely. The prostate gland is large, larger than the ampulla of the atrium, runs into the atrium laterally, in the middle through a short slender stalk. The length of the ampulla of the atrium is 132-162 µm, diameter in the region it joins the prostate gland is 38-58 µm, diameter of the vas efferens is around 30 µm. Length of the penial sheath 166-182 µm, diameter in the middle 23-24 µm, where it narrows 16-18 µm, greatest diameter of the funnel-shaped expansion on the proximal end 25-40 µm. Length of penial sac 185-195 µm, diameter 75-85 µm. Ampulla of spermatheca dual-chambered, with more voluminous and thin-walled upper chamber, both characters round. Height of upper chamber 195, diameter 166, height of lower chamber 120, diameter 113 µm; length of spermathecal duct 210 µm, diameter in ampulla 70, at body wall (at exit) 33 µm. Spermathecae contain long, lanceolate spermatozeugmata. (ref. ID; 7924)

Remarks

T. heterodontus sp. n. is the closest to the other species of Tasserkidrilus to T. mirandus based on the number of setae per bundle, the structure of the dual-chambered spermatheca and vas deferens being ciliated only in the proximal part, based on the shape of the short, cylindrical atrium and tubular penial sheath. T. heterodontus differs from T. mirandus in having smaller setae, which in T. heterodontus on the anterior segments have short, rudimentary teeth or are lacking them (inner single-tipped setae of the bundle), while in T. mirandus on all segments setal teeth are well developed; the vas deferens in T. heterodontus is 0.50 times as long and narrower, the atrium smaller in size, it has a short vas efferens; the penial sheath is less arched, does not have on the distal end as considerable an expansion and is not covered with spines, as is the case in T. mirandus, the penial sac is shorter and narrow; the spermatheca has a longer duct relative to the length of the ampulla and contains spermatozeugmata of a different shape (in T. mirandus, they are longer, worm-shaped). (ref. ID; 7924)

Etymology

From Latin heterodontus, with different teeth. (ref. ID; 7924)

Examined materials

Two sexually mature specimens; southern Lake Baikal, Solzan region, depth 7.5 m, muddy sand; 22 July 1975. One sexually mature specimen (fragment of anterior part of body); southern Lake Baikal, Mangutay, depth 5 m, weakly muddy sand; 30 July 1987. Holotype No.T-286: sexually mature specimen 8 mm long with greatest diameter of 480 µm, dissected, mounted in glycerin. (ref. ID; 7924)

Type materials

Holotypes and type materials are deposited in the collection of Limnological Institute, Siberian Division, Russian Academy of Sciences, Irkutsuk. (ref. ID; 7924)

Tasserkidrilus rectitubifer Snimschikova & Akinschina, 1993 (ref. ID; 7924 original paper)

Diagnosis

T. rectitubifer sp. n., based on external characters, is very close to T. heterodontus. They resemble one anther based on the shape of the bifid setae, and in both species the length of the teeth in the same bundle differs and increases gradually from the inner setae to the outer ones; in addition, the length of the teeth increases on each subsequent segment from II to VIII, and on the postclitellar segments the teeth of the setae are identical, of medium length. Unlike T. heterodontus, T. rectitubifer have no single-tipped setae on the anterior segments, and the number of setae per bundle is greater (up to 6-7). The tubular penial sheaths are also quite similar, but in T. rectitubifer, the tube is straight, shorter and wide, its funnel-shaped base is flatter than in T. heterodontus and on the distal end, the tube expands a little and is rounded, thus differing from the simply cut-off tube in T. heterodontus. (ref. ID; 7924)

Descriptions

Length of fragment about 2 mm, greatest diameter 480 µm. Coloration light brown, integument not translucent, dense. Prostomium small, rounded, not quite as long as wide at the base. Annularity distinct, intersegmental furrows rather deep. Segments II-VII biannulate, anterior furrow 0.33 times as wide as posterior. Setal bundles located on wide furrow. Setal tubercles very small, inconspicuous. Setae only bifid, of the same form in dorsal and ventral bundles, with distal nodulus located at one-third of the length of the seta. On the anteclitellar segments, the teeth of the setae are of different length in the same bundle; on the inner (middle) setae, the teeth are half the length of the teeth on outer (lateral) setae, and the innermost seta of the bundle has a variable number of teeth, on the following setae the length of the distal tooth increases more than on the proximal, and on the outermost seta the distal tooth is two times as long as the proximal. The length of the setae, their number per bundle as well as the length of the teeth increase gradually from segment II to VIII. Beginning with segment VIII, all setae are identical in form, with a varying number of teeth, the teeth are of medium length, and the proximal one is thicker than the distal. On segments II-III, there are four setae per bundle, 50-54 µm long, on segments IV-V (4) 5-6 per bundle up to 65 µm long, on VI-VII 6-7 per bundle 65-72 µm long, and on VIII-X 5 setae per bundle 55 µm long. The penial sheath is in the form of a straight tube (hence the name of the species) with a wide and flat funnel-shaped base and weak expansion on the distal end, as if abutting the body wall, the tube expands a little and is rounded, the opening of the tube is directed straight down. Length of the penial sheath 162 µm, diameter of middle part 28, of the expansion at the distal end 33, greatest diameter of funnel-shaped base 65 µm. Unfortunately, we could not describe the structure of the gonoducts which were destroyed in the dissection. (ref. ID; 7924)

Etymology

From Latin, rectitubifer, having a straight tube. (ref. ID; 7924)

Examined materials

One sexually mature specimen (fragment of anterior section of body, consisting of 14 segments); southern Lake Baikal, Mangutay, depth 5 m, sand-mud; 30 July 1987. Sole specimen, holotype No.T-287, is preserved in a whole mount in glycerin. (ref. ID; 7924)

Type materials

Holotypes and type materials are deposited in the collection of Limnological Institute, Siberian Division, Russian Academy of Sciences, Irkutsuk. (ref. ID; 7924)

Tasserkidrilus timmi Snimschikova & Akinschina, 1993 (ref. ID; 7924 original paper)

Diagnosis

Setal apparatus of T. timmi sp. n. very distinctive. Based on the shape of the anteclitellar setae and on their number per bundle (usually two), immature representatives of this species are easily confused with lumbriculids, and sexually mature representatives may also be confused with the Baikal endemic genus Lycodrilus Grube, 1873, if only external characters are examined (produced, slender body, large, apparently single-tipped setae, Limnodrilus-like penial sheath). However, the structure of the reproductive system of T. timmi entirely corresponds to the general plan of the reproductive system of the genus Tasserkidrilus: dual-chambered ampulla of the spermatheca filled with spermatozeugmata; vas deferens ciliated only in proximal part and entering atrium apically; cylindrical atrium with very short vas efferens, with prostate gland entering in the middle; penial sheath with funnel-shaped base, tubular continuation, weakly expanded distally and obliquely cut along edge. (ref. ID; 7924)

Descriptions

Medium sized. Coloration from light brown to yellow or gray yellow. Body length 7-10 mm, greatest diameter in region of clitellum 520-540 µm, number of segments more than 30 (all sexually mature specimens without caudal segments). Prostomium triangular, about as long as wide at the base, prolobous. Segments II-VI (more rarely II-VIII) biannulate, anterior furrow half the width of the posterior. Base of setal bundles located on furrow, that is, at the very start of the wide furrow. All postclitellar segments uniannulate. Setal tubercles small, rise slightly above body surface, their height not more than 5 µm. Integument dense, not translucent, thickness of body wall 27 µm. Chloragogen tissue begins with segment VI. Two type of setae: anteclitellar dorsal and ventral setae, uniform in shape, lumbricine, with samll triangular rudiment of the proximal tooth, which, beginning with segment II, is set increasingly lower on subsequent segments, and is particularly low on setae of segments VI-VII. Because of this, the disappearing tooth looks like a foreign growth or, figuratively speaking, something that is slapped on the large seta that is apparently single-tipped; and postclitellar setae, bifid, with short teeth of equal or nearly equal length, diverging at a right angle. Each bundle on the anteclitellar segments had 2-3 (more often 2) setae 76-90 µm long (on segments II and III), 100-132 µm (on segments IV-X); sometimes next to them 1-2 rudiments of young setae 17-45 µm long are present. Each bundle on the postclitellar segments has two setae (rarely one) 56-75 long. There are no hair or fan setae. In sexually mature specimens ventral setae on segment XI are absent, there are no modified gential setae. Clitellum ringlike, slightly raised, takes up segments X-XII. Spermathecal openings on segment X are lateral tothe line of the ventral setae, the male gonopores on segment XI are at the location of the absent ventral setae. One pair of testes on segment X on septum 9/10, one pair of ovaries on segment XI on septum 10/11. One pair of seminal funnels up to 100 µm in diameter and up to 45 µm deep situated on septum 10/11, opening on segment X. Vas deferens in proximal part (about one-third of entire length) ciliated, in distal part not ciliated. Length of vas deferens 825-1020 µm, diameter of proximal part 20-23 µm, of middle and distal part 36-39 µm. Vas deferens enters atrium apically. Atrium small, cylindrical, proximally and distally narrowed, with very small vas efferens, terminates in penis provided with sheath and placed in a large penial sac. The penial sheath has a funnle-shaped base, tubular, slightly arched, continuation and weak expansion at the distal end, the margin is somewhat obliquely cut, the opening directed down and slightly to the side. Length of ampulla of atrium up to 132 µm, greatest diameter in the middle 36-40 µm, diameter of proximal narrowing 30 µm, diameter of vas efferens 27-30 µm. Length of penial sheath 165-185 µm, diameter in the middle 20-23 µm, greatest diameter of funnel-shaped proximal expansion 30-33 µm, of distal expansion up to 26 µm. Length of penial sac 170-200 µm, diameter in proximal part 72-92 µm, indistal part 53-66 µm. Prostate gland large, trilobate, with amorphous margins, lobes turn in, enveloping the atrium. Gland opens into the atrium in the middle or its distal half through a well-defined stalk. The ampulla of the spermatheca is dual-chambered, both chambers are spherical or ovoid, the upper one usually being larger. Height of the upper chamber 211, diameter 200, height of lower chamber 200, diameter 150 µm. In another specimen, the height of the upper chamber is 165 µm, diameter 155, for the lower chamber 165 and 158 µm, respectively. The spermathecal duct well differentiated, comparatively short, 140 to 150 µm long. There are lanceolate spermatozeugmata 108-130 µm long. (ref. ID; 7924)

Remaks

Of all species of Tasserkidrilus, T. timmi is closed to T. mirandus based on the structure of the dual-chambered spermatheca with well-defferentiated spermathecal duct of medium length; ciliated vas deferens in its proximal part; penial sheath in form of long, arched tube expanded at both ends in the form of a funnel. T. timmi differs from T. mirandus in the shape of the anteclitellar setae, their size and number per bundle; in the length of the vas deferens (in T. mirandus, two times as long), the shape of the atrium, which in T. timmi is more expanded and has a short vas efferens, and in the size and nature of the expansion of the distal end of the penial sheath, which externally is covered with spines only in T. mirandus. (ref. ID; 7924)

Etymology

The new species is named in honor of Tarmo Eval'dovich Timm, the noted Estonian hydrobiologist and zoologist. (ref. ID; 7924)

Examined materials

Ten specimens, of which four are sexually mature; southern Lake Baikal, Salzan region, depth 25 m, muddy sand, 12 July 1991; 7 specimens, of which one is sexually mature; same place, 59 m, mud with mixture of sand, 12 July 1991. Holotype No. T-285, sexually mature specimen 8.5 mm long with greatest diameter of 0.5 mm, dissected, mounted in glycerin. (ref. ID; 7924)

Type materials

Holotypes and type materials are deposited in the collection of Limnological Institute, Siberian Division, Russian Academy of Sciences, Irkutsuk. (ref. ID; 7924)