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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Rhizodrilus

Rhizodrilus F. Smith, 1900 (ref. ID; 1923, 5957)

Family Tubificidae: Subfamily Rhyacodrilinae (ref. ID; 5882, 7824)

Synonym Torodrilus Cook, 1970 (ref. ID; 5957)

ref. ID; 1923

Ventral setae ordinarily cleft; spermatheca if present usually open on segment 10; usually reddish in appearance, commonly more than 25 mm in length, many live in tubes. Body surface not covered with many cuticular papillae. Dorsal bundles without hair setae. With a single spermathecal pore in the median portion of segment 10; sperm ducts without definite prostate glands. Single species. Chen (1940) considers Rhizodrilus a synonym of Monopylephorus. (ref. ID; 1923)

ref. ID; 5957

Tubificid oligochaetes with male ducts having a vas deferens which usually enters the tubular atrium subapically, atrium with diffuse prostate glands, terminating in either an ejaculatory duct which exits on the inner aspect of large ventrolateral papillae or into the median copulatory bursa or as an eversible pseudopenis opening into median copulatory bursae. Modified spermathecal and (or) penial setae present. Some part or all of the spermathecal equipment occupies segment IX as well as or instead of X. Sperm in the spermathecae as loose masses or in oriented bundles, not in spermtozeugmata sensu strictu. Coelomocytes small or absent. Spermathecal glands usually present. Freshwater or coastal locations, U.S.A.; Pacific coast of Canada; Southwest Africa; Queensland, Australia. (ref. ID; 5957)

Remarks

In the type species R. lacteus, the spermathecae lie in X, with the pores at the anterior edge of the segment to the common pores of the modified prespermathecal setae and their associated "glands" which lie in IX. The ventral setae of X may also be modified and associated with similar long, cylindrical so-called glands with narrow lumina. In a second species, Monopylephorus africanus, the spermathecae open behind the (unmodified) ventral setae of IX rather than anteriorly in X; no spermathecal setae or spermathecal glands are present, but the description of the species, and what could be seen on the single type in fluid, strongly suggest it is related to lacteus (already noted by Brinkhurst (1963)). Monopylephorus pacificus can now be described in better detail than before (Brinkhurst and Baker 1979) and it is clear that not only do the male ducts resemble those of lacteus but the modified spermathecal setae and associated spermathecae plus glands are in IX, not X. The male reproductive ducts also terminate in a median copulatory bursa which largely fills XI (? hence the need for the forward shift of the spermathecae as the atria largely fill X instead of the usual XI). Dr. C. Erseus (personal communication) pointed out to us that we should consider Torodrilus lowryi, Rhyacodrilus arthingtonae, and (after the redescription by Holmquist (1974) Telmatodrilus multiprostaus in the assemblage that we now recognize as the genus Rhizodrilus. The latter proves, on reexamination of the types from the Australian Museum (W4178-4182), to be related to Telmatodrilus as originally suggested (Brinkhurst 1971), as the prostate glands are clearly multiple on each atrium though arranged somewhat differently to those of the type species of the genus. When the species was redescribed by Holmquist (1974) only the holotype and paratype were examined, and none of the material still in the Brinkhurst collection was. In the holotype (a dissected specimen) the segmental position of the spermathecal setae and their associated glands cannot be determined. The serial sections of the paratype examined by Dr. Holmquist shows the spermathecal setae and glands clearly in segment IX rather than X, and so the description was amended to show this. However, all of the paratypes, except the single sectioned specimen examined by Holmquist, prove to have the spermathecal setae in the normal position as originally illustrated. As all the paratypes also have distinct multiple prostates the possible relationship between T. multiprostatus and members of the genus Rhizodrilus will not be discussed futher here. The five species that are contained in the genus Rhizodrilus are characterized by the involvement of segment IX in the spermathecal equipment. This involvement ranges from "conspicuous elliptical papillae postero-median to the ventral bundles in IX, each with a short diagonal groove passing posterolaterally from its centre to intersegment 9/10" (Jamieson 1978) in arthingtonae, to the possession of spermathecal setae and even spermathecae in IX instead of X (pacificus). The penial setae are modified in all species, the voluminous setal sacs joining the median male bursae in dominating segment XI. The atria in Rhizodrilus are covered with prostate cells which may appear to form a lobed mass. The prostate cells may penetrate the muscular walls of the atria in groups rather than as single cells. In R. lowryi the prostate cells are believed to invest the ectal part of the vas deferens (Cook 1970). The sperm in the spermathecae occurs in loose masses in the scant material of the type species, in a mixture of organized bundles and loose masses in arthingtonae, in organized bundles in lowryi, and in peculiar club-shaped bundles in pacificus. Although the type species, R. lacteus and R. africanus have many coelomycetes (anteriorly at least), the other three species of the genus have few or none. This lack of coelomocytes in some species of the genus opens the possibility of including the monotypic Branchiura in the Rhyacodrilinae instead of isolating it in the Branchiurinae. (ref. ID; 5957)

Type species

Rhizodrilus lacteus Smith, 1900 (ref. ID; 5957)
  1. Rhizodrilus africanus (Michaelsen, 1913) nov. comb. (ref. ID; 5957)
    Syn; Monopylephorus africanus Michaelsen, 1913 (ref. ID; 5957)
  2. Rhizodrilus arthingtonae (Jamieson, 1978) nov. comb. (ref. ID; 5957)
    Syn; Rhyacodrilus arthingtonae Jamieson, 1978 (ref. ID; 5957)
  3. Rhizodrilus lacteus F. Smith, 1900 (ref. ID; 1923, 5957)
    Syn; Monopylephorus lacteus (Smith) Brinkhurst, 1963 (ref. ID; 5957)
  4. Rhizodrilus lowryi (Cook, 1970) nov. comb. (ref. ID; 5957)
    Syn; Torodrilus lowryi Cook, 1970 (ref. ID; 5957)
  5. Rhizodrilus pacificus (Brinkhurst & Baker, 1979) nov. comb. (ref. ID; 5957)
    Syn; Monopylephorus pacificus Brinkhurst & Baker, 1979 (ref. ID; 5957)

Rhizodrilus africanus (Michaelsen, 1913) nov. comb. (ref. ID; 5957)

Synonym

Monopylephorus africanus Michaelsen, 1913 (ref. ID; 5957)

Descriptions

Length 16 mm, 84 segments. Setae bifid, up to 4 per bundle, median setae with teeth equally long, the lower thicker than the upper; penial setae 4-5 per bundle. Vas deferens long, entering atrium subapically, atrium tubular, covered with prostate cells, leading to ejaculatory duct that opens into upright copulatory chamber that bears penial setae posteriorly. Male pore median; spermathecal pores on transverse median swelling behind setae of IX, pores themselves in setal line in front of 9/10, spermathecae in IX. Coelomocytes numerous. Crocodile River, Witporte (west of Johannesburg), South Africa. (ref. ID; 5957)

Remarks

The position of the spermathecae is confirmed after examination of the holotype by R.O. Brinkhust. The penial setae seem to be about twice the size of the normal setae, as described by Michaelsen (1913). The lining cells of the atrium seem to be cubical, and the ducts as described must be very similar to those of R. lactues. The spermathecae are totally within IX in this species, but as the pores are at the posterior limit of the segment instead of the anterior limit as usual (in X), this position is clearly secondary. This forward shift seems to be associated with the occupation of much of XI by the male terminalia, leading to the extension of the atria and vasa deferentia into X, the spermathecae being pushed forward even further. The form of the sperm in the spermathecae remains unknown. In Bothrioneurum (in which the vas deferens and part of the atrium protrude into X and the copulatory bursae and paratria fill XI) the spermathecae are missing instead of being shifted forward and external spermatophores are developed. The presence of large number of coelomocytes was confirmed by examination of the type by R.O. Brinkhurst. The precise point of entry of the vas deferens and into the atrium was not confirmed on the type, but Michaelsen's original drawing shows it very clearly; the redrawn version in Brinkhurst (1971) is less clear. (ref. ID; 5957)

Material examined

Zool.Mus.Univ.Hamburg (Michaelsen collection): cat. 7496 holotype, in fluid (sectioned specimen destroyed). (ref. ID; 5957)

Rhizodrilus arthingtonae (Jamieson, 1978) nov. comb. (ref. ID; 5957)

Synonym

Rhyacodrilus arthingtonae Jamieson, 1978 (ref. ID; 5957)

Descriptions

Length 66 mm, width 1.8 mm, 160 segments. Setae all bifid with the upper tooth thinner and usually longer than the lower, penial setae with upper teeth shorter than the lower, curved distal to nodulus with heads closely grouped, shafts long, straight and diverging. Accessory genital markings, a pair of conspicuous elliptical papillae posteromedian to ventral bundles of IX, each with a short diagonal (seminal) groove passing posteriolaterally from its centre to 9/10; spermathecal pores small and indistinct, at 9/10 on the lateral line. Male pores on large equatorial papillae, turned in towards the ventral midline so as to be almost contiguous, the lateral border of each papillar indefinite, in the ventral setae lines. Vas deferens (of each side) coiled anteriorly in XI before entering atrium about one third from ental end, vas deferens at least twice the length of the atrium, atrium covered with compact prostate which communicates with the lumen at numerous points. Ejaculatory duct slender, entering male porophore in contact with penial setal sac. Sperm free and in organized bundles in the spermathecae. Coelomocytes not apparent. North Stradbrook Island, Queensland, Australia. The locality here is Brown Lake, a perched acid lake on an island, 2.25 km from the sea. (ref. ID; 5957)

Remarks

The lack of coelomocytes, presence of bundles sperm and the genital papillae in IX strongly suggest a relationship to the other species in the genus. As the spermathecal setae are unmodified the characteristic glands are absent, as in R. africanus. The atria are essentially the same as those in other species. (ref. ID; 5957)

Material examined

Specimens from the B.G. Jamieson collection, part of the type series (now in the Queensland Museum, cat. G8881-8882). (ref. ID; 5957)

Rhizodrilus lacteus F. Smith, 1900 (ref. ID; 1923, 5957)

Synonym

Monopylephorus lacteus (Smith) Brinkhurst, 1963 (ref. ID; 5957)

Descriptions

Length 70-100 mm, 0.4-0.6 mm wide; 215-365 segments. Clitellum X-XII. Dorsal and ventral setae similar in size, shape, number, anteriorly 5-6 bifids, posteriorly 1-4, lower tooth broader than upper, ventral setae of IX single, large, spatulate; ventral setae of X normal or modified as in IX; 4-6 penial setae in each ventral bundle of XI with thickened, rounded tips. Spermathecal pores small, paired, in setal line in 9/10; ventrolateral surfaces of XI folded to form prophores enclosing median copulatory bursa; true male pores inconspicuous on inner aspect of porophores. Penial setal sacs open into median bursa posteriorly, bearing small glands. Male ducts (all structure paired) with large sperm funnel, fairly thick vas deferens of some length which winds before opening into atrium subapically; atrium, long, tubular, covered with diffuse prostate cells except along narrow basal strip, atrium with tall collumnar lining cells but with muscle layer absent or indistinct; narrow ejaculatory duct penetrates vacuolated cells and muscles to open on side walls of copulatory bursa. Spermathecae with short, indistinct ducts, ampullae spherical, sperm in loose masses. Spermathecal setae accompanied by long tubular glands composed of tall cells surrounding a narrow lumen with a thin external covering of cells. Coelomocytes spherical, abundant anteriorly. Flag Lake, Havana, Illinois (near Peioria on the Illinois River); Upper Three Runs, Aiken Co., South Carolina, U.S.A. (ref. ID; 5957)

Remarks

This description confirms and extends that of Smith (1900). The species is so characteristic that it cannot have been overlooked in the many surveys of the last decade and so it must be truly rare. Rhizodrilus lacteus was regarded as the type species of Rhizodrilus when that genus was held to include those species referred to Monopylephorus and Peristodrilus but with M. rubroniveus as a species spuria (Hrabe (1967) for example). (ref. ID; 5957)

Material examined

  • U.S.N.M. cat. 24589, serial sections labelled 0-216a-0-216c, Lectotype acc. D.G. Cook. 24589-24590, 26281-26282 labelled paralectotypes D.G. Cook. (ref. ID; 5957)
  • Brinkhurst collection: Whole mount, several specimens, Upper Three Runs, South Carolina. (ref. ID; 5957)

    Rhizodrilus lowryi (Cook, 1970) nov. comb. (ref. ID; 5957)

    Synonym

    Torodrilus lowryi Cook, 1970 (ref. ID; 5957)

    Descriptions

    Length 20-26 mm, 62-94 segments. Body wall bearing small transverse ridges with adhering foreign matter. Dorsal and ventral bundles with 4-6 bifid setae, posteriorly 2-3 simple pointed or faintly bifid setae with rudimentary upper teeth; ventral setae of IX single, large, spoon-shaped spermathecal setae, ventrals of X unmodified, ventrals of XI with thickened, round-ended, penial setae. Spermathecal setae associated with glands. Spermathecal pores in the lateral line of 9/10. The 9/10 furrow also with a midventral papilla with a small pit on each lateral surface. Ventral surface of XI deeply infolded to form porophores; male pores open into deep longitudinal folds median to porophores, penial setae inserted posterior and median to male pores. Male funnel (of each side) leads to narrow vas deferens which joins cylindrical, erect atrium more or less apically, atrium with apical swelling; ejaculatory duct simple; prostate gland a loose mass covering anterior and dorsal part of atrium and (?) vas deferens. Spermathecae with short indistinct ducts and ovoid ampullae, sperm in organized masses. Coelomocytes few, small. Anvers Island, Kerguelen Island, Southern Indian Ocean. (ref. ID; 5957)

    Remarks

    Cook (1970) remarked on the many similarities between this species and both Monopylephorus lacteus and M. africanus (as they were then designated), but was largely deterred from placing the species in the Rhyacodrilinae because of the lack of coelomocytes. This objection has now been removed. Examination of new material loaned to us by Dr. P. Lassere via Dr. C. Erseus has been used to confirm several points in the original description. (ref. ID; 5957)

    Material examined

    Mus.Hist.Nat.Paris, cat. AS428-AS460. Kerguelen Island, Golfe du Morhiban, en bordure de la Fosse de l'Oceanographie, 51 m, 21 May-17 July, 1975. coll. D. Desbruyeres (courtesy P. Lasserre, C. Erseus). (ref. ID; 5957)

    Rhizodrilus pacificus (Brinkhurst & Baker, 1979) nov. comb. (ref. ID; 5957)

    Synonym

    Monopylephorus pacificus Brinkhurst & Baker, 1979 (ref. ID; 5957)

    Descriptions

    Length to 15 mm; width at XI up to 1.2 mm; up to 100 segments. Setae 1-3 (4) anteriorly, 1, 2 posteriorly, all with upper tooth much longer and thicker than lower; spermathecal setae single (rarely paired) in each ventral bundle of IX; ventral setae of X normal; penial setae with bifid tips, up to 270 µm long, up to 9 per bundle. Spermathecae in IX with pores close to 9/10, spermathecae empty into a transverse slit connecting the two spermathecal pores; slit preceded by transverse thickening of cuticle. Spermathecal setae associated with long cylindrical glands with narrow lumen. Spermathecal setae and associated glands open just anterior to spermathecal pores. Spermathecae with large, thick-walled ampullae and short thick duct. Sperm in elongate bundles (? with "spiked" heads). Male duct (system paired) with large ventrolateral sperm funnel, ciliated vas deferens penetrates 10/11 but runs forward in sperm sac to anterior part of X where it joins the atrium subapically. Atrium with tall lining cells and distinct muscle layer covered with external prostate cells (may penetrate muscle layer in clusters). Ejaculatory duct enters large median bursa dorsolaterally; ejaculatory duct expands to form a voluminous muscular sac before entering the less muscular median bursa; both enclosed in connective tissue and peritoneum; retractor muscle attached to roof of XI and XII. Penial setae enter bursa posteriorly. Bursa largely fills XI and opens mid ventrally through a single opening. Coelomocytes few or absent. Coastal British Columbia; Japan. (ref. ID; 5957)

    Remarks

    This description corrects two omissions in the earlier account (Brinkhurst and Baker 1979). New material has made it possible to determine that the spermathecae are in IX, as in R. africanus, again with pores just ahead of 9/10 rather than at the anterior edge of X. The spermathecal setae and glands resemble those of R. lacteus. The penial setae are of the usual Rhyacodriline type, as in R. africanus. The transition between the atrial tissue and ejaculatory duct is very remarked. The atrial muscle layer is thin, whereas the granular atrial tissue layer is quite thick. The ejaculatory duct has a very thick muscle layer and a very thin layer of cells about the lumen. The ejaculatory duct does not appear not be ciliated. As the ejaculatory duct approaches the median bursa the lumen changes from a circular to a fine-pointed star shape. This star-shaped lumen is obscured as the muscular sac forms. The odd sperm bundles seen in the Japanese material differ slightly from those in the Canadian specimens. The heads of the sperm bundles in the Canadian specimens lack the 'spiky" projections of the Japanese material but do display a definite structure. The sperm bundles in the Canadian specimens are also larger and much thicker than those of the Japanese specimens. The sperm bundles in both the Japanese and Canadian specimens do not lie "naked" in the spermathecae but are enclosed in very thin walled "sacs". Except for the above differences in form of the sperm bundles, the Japanese and Canadian specimens are very similar morphologically. As the range of variation of the form of sperm bundle in R. pacificus is not yet known, the Japanese specimens are regarded here as belonging to pacificus. (ref. ID; 5957)

    Material examined

  • U.S.N.M. cat. 55376, 55377, holotype and paratypes. Port Alice, B.C. (ref. ID; 5957)
  • U.S.N.M. cat. 61981-61984, additional material, 3 whole mounted specimens, and 2 slides of sections, Bamfield, B.C., coll. H.R. Baker. (ref. ID; 5957)
  • NMCIC 1980-1503, 1504, 1505, additional material, 2 whole mounted specimens, and 2 slides of sections, Bamfield, B.C., coll., H.R. Baker. (ref. ID; 5957)
  • Brinkhurst collection: Porpoise Harbour, Moyeha River, Cowichan Bay, Port Alice, Britisch Columbia, coll. K. Conlan, K. Coastes, C. Levings, 10 whole mounts and sections various dates 1977-1979. (ref. ID; 5957)
  • Baker collection: Bamfield Inlet, various dates, many. Aristazabal Is., May 19, 1980, many. Flores Island, May 23, 1980. Espinosa Inlet, May 27, 1980. All British Columibia, coll. H.R. Baker, whole mounts and sections. Rishiri Island, Hokkaido, Japan, August, 1963, coll. M. Imajima, whole mounts and sections. (ref. ID; 5957)