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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Stylodrilus

Stylodrilus Claparede, 1862 (ref. ID; 1257, 3692, 7265)

Family Lumbriculidae (ref. ID; 1257, 1928, 5876, 5939, 6422, 6451, 7265, 7854)

ref. ID; 1663

Setae all of one form, single-pointed bifid or both. Four bundles of two setae each per segment. Usually reddish or brownish worms. 20 to 50 mm long. In mud or debris of pools, ponds and lakes. One pair of male gonopores on X. Prostomium without a proboscis. (ref. ID; 1663)

ref. ID; 7265

Diagnosis

Diagnosis of the genus (modified from Cook 1971); Setae single-pointed, bifid, of both. Interstitital forms may have thin, elongate, hairlike dorsal setae, which are absent in anterior segments. One pair of male pores behind ventral setae on segment X, rarely on IX. One pair of spermathecal pores behind ventral setae on IX, rarely on VIII. Posterior lateral blood vessels often present. Two pairs of testes in IX and X, rarely in VIII and IX. Two pairs of male funnels and vasa deferentia, the anterior pair plesiopore and the posterior pair prosopore; vasa deferentia joint atria proximally to apically. One pair of spherical to tubular atria in X, rarely in IX. One pair of ovaries in segment behind last testis-bearing segment. Spermathecae paired in the preatrial segment, with well-differentiated duct and ampulla. (ref. ID; 7265)

Remarks

The genus Stylodrilus Claparede, 1862 was revised by Brinkhurst (1965) to include Bythonomus Grube, 1879. In a previous work, Chekanovskaya (1962) had pointed out that the division of Stylodrilus and Bythonomus was not satisfactory. Since then, different opinions have been expressed about the synonymy of the genera, advocating it (Cook 1968, 1971; Sokolskaya 1975; Giani and Martinez-Ansemil 1984, and others) or rejecting it (Hrabe 1970). Cook (1975) proposed a subgeneric rank for Bythonomus that include those species with single-pointed setae. However, several genera in Lumbriculidae include species with bifid and simple-pointed setae, and setal morphology is no longer considered a definitive character for generic rank in the family. The hairlike setae in interstitial hyporheic lumbriculids seem to be convergent in a number of genera, and the structure of the genitalia is regarded as the basis for generic classification of lumbriculid species. (ref. ID; 7265)
  1. Stylodrilus asiaticus (Michaelsen, 1901) (ref. ID; 3692)
  2. Stylodrilus aurantiacus (Pierantoni, 1904) (ref. ID; 6618)
  3. Stylodrilus beattiei (ref. ID; 5939)
  4. Stylodrilus brachystylus Hrabe, 1928 (ref. ID; 6618)
  5. Stylodrilus californianus Rodr., 1996 (ref. ID; 6651)
  6. Stylodrilus cernosvitovi Hrabe, 1950 (ref. ID; 3692)
  7. Stylodrilus chukotensis (Sok., 1975) (ref. ID; 6651)
  8. Stylodrilus crassus (Isossimoff, 1948) (ref. ID; 3692)
  9. Stylodrilus gabretae Vejdovsky, 1882 (ref. ID; 1928)
    See; Stylodrilus heringianus (ref. ID; 1257)
  10. Stylodrilus hallissyi Southern, 1909 (ref. ID; 1928 original paper)
  11. Stylodrilus heringianus Claparede, 1862 (ref. ID; 1257, 1911, 3692, 7265) reported year? (ref. ID; 3704, 3955, 4491, 6607, 7817) reported author and year? (ref. ID; 5939)
    Syn; Stylodrilus gabretae Vejdovsky, 1882 (ref. ID; 1257); Stylodrilus vejdovskyi Benham, 1891 (ref. ID; 1257)
  12. Stylodrilus lemani (Grube, 1879) (ref. ID; 6618) reported year? (ref. ID; 6609, 7817) reported author and year? (ref. ID; 6451)
  13. Stylodrilus leucocephalus Hrabe, 1931 (ref. ID; 6620)
  14. Stylodrilus mirus (Chekanovskaya, 1956) (ref. ID; 7265)
  15. Stylodrilus opisthoannulatus (Isossimoff, 1948) (ref. ID; 3692), (Isossimov, 1948) (ref. ID; 7265)
  16. Stylodrilus parvus (Hrabe & Cernosvitov, 1927) (ref. ID; 3692, 7265)
  17. Stylodrilus sowaliki (Holmquist, 1976) (ref. ID; 6651)
  18. Stylodrilus suputensis Timm, 1995 (ref. ID; 6651, 7854)
  19. Stylodrilus tschaunensis Morev, 1982 (ref. ID; 6651) reported year? (ref. ID; 7893)
  20. Stylodrilus vejdovskyi Benham, 1891 (ref. ID; 1928)
    See; Stylodrilus heringianus (ref. ID; 1257)
  21. Stylodrilus wahkeenensis Rodriguez & Coates, 1996 (ref. ID; 6651, 7265 original paper)

Stylodrilus hallissyi Southern, 1909 (ref. ID; 1928 original paper)

Descriptions

These worms vary from 20 mm when contracted to 50 mm when expanded. Individually they also vary very much in size. Their movements are decisive and rapid, and distinguish them easily from the Tubificidae, with which they are usually associated. The cuticle is smooth, or with rings of clear glands. These is a longitudinal band of circular cells in a line with each pair of setae, running along the whole body-length. The prostomium is conical, and is thickly covered with colourless round glands. The setae are paired, and are all distinctly bifid. The upper tooth is much smaller than the lower one, and the node is in the distal half. The clitellum occupies segments 10-12. It is formed of oval cells full of round globules, with clear spaces between them. The segments are composed of two rings, the larger of which is 4-6 times as broad as the smaller one. In the anterior segments the smaller ring is very narrow. The intestine is covered with greenish-brown bladder-like cells, which commence in the 6th segment. The brain is formed of two lobes, which are shorter and broader than those of Stylodrilus gabretae Vejdovsky. The two lobes are connected near the anterior end, so as to make the anterior concavity shallow, the posterior one deep. The first nephridium has its funnel in the 6th segment, and opens to the exterior on the 7th. The second nephiridium similarly occurs in segments 12 and 13. Behind this there is usually a pair of nephridia in each segment. They are very long and much folded, and stretch through several segments. The funnel is rosette-shaped, and composed of several cells. Immediately behind the septum there is a large glandular structure, brown in colour. The first part of the ciliated duct which follows is long and folded. The next part is invested by a covering of clear gland-cells, which the duct pierces several times. This part of the nephridium is closely applied to the ventral vessel. Transverse sections show three or four ducts piercing the glandular covering. The slender duct finally emerges, and runs alongside the proximal portion up to the glandular swelling near the septum. Here it branches off, and goes straight to the external pore. This glandular structure has not been described in any other species of Stylodrilus. In S. heringianus Claparede figures the nephridium as a simple slender tube; and Benham states that in S. vejdovskyi the nephridia resemble those figured by the Claparede. The arrangement of the nephridia in this genus agrees with the description of Phreatothrix pragensis, as given in the text by Vejdovsky; but in the figure the segments are numbered one further behind. These numbers are copied by Beddard, and Michaelsen. The second pair of nephridia are shown with a short glandular investment, somewhat resembling that of the present species; but the other nephridia are without it. The reproductive organs agree very closely with those of S. heringianus. The spermathecae are in the 9th segment. They have an almost spherical ampulla, and a slender duct of about the same length. There is no crystal in the ampulla. The male ducts open at the back of the 10th segment. The penis are pointed, and about as long as half the diameter of the body. The atrium is oval and thickly coated with the prostate glands. The testes lie in segment 9 and 10. The first pair are attached to the anterior septum; the second pair lie on the floor of the segment. The ovaries are attached to the front of segment 11. The oviducts are short and wide, and open between the 11th and 12th segments. There are two pairs of sperm-sacs, the first pair being small and confined to segment 8. The second pair commence in segment 9, and may stretch as far back as the 21st segment, according to the stage of maturity. (ref. ID; 1928)
  • Vascular system: It is the vascular system of the species which chiefly characterizes it. The most striking characteristic of the family Lumbriculidae, and one which distinguishes it from all other Oligochaeta, is the occurrence of blood-glands or blind contractile appendages to the blood-vessels. These appendages are usually covered with chloragogen-cells, and possibly some interaction takes place between these cells and the blood. On the other hand these is evidence to show that these contractile sacs have a respiratory function. The genus Stylodrilus has hitherto been distinguished from all other European genera of the Lumbriculidae by the absence of these blind appendages. The genus was founded by Claparede in 1861. Speaking S. heringianus, the first known species, Claparede says: - "The vascular system is formed of dorsal and ventral vessels placed in communication with each other, in each segment, by an intestinal branch and a perivisceral branch". Vejdovsky says about S. gabretae: - "The blood-vessels do not show lateral branching". The remaining species, S. vejdovskyi was described by Benham, who makes only a slight reference to the vascular system, from which one may infer that it is not remarkable in any way. The present species differs markedly in its vascular system from all other members of the genus. The commissural vessels, instead of being two pairs in each segment, as Claparede says, are confined to the anterior 13 segments. There are two pairs of them in each of the segments; and they are very long and folded. The vessels of the 13th segment are extremely long in the mature animal, and ramify freely over the walls of the ovisacs and spermsacs, increasing in length as these develop. They often extend back so far as 21st segment. Behind the 21st segment there is no direct connection between the dorsal and ventral trunks. The ventral vessel is formed in the 5th segment by the union of the two anterior commissures. As the dorsal vessel is traced backwards, it begins to show indications of short, blind offshoots. In the last 30 segments or so of the tail these become very conspicuous. There are two pairs in each segment, situated close to the anterior and posterior septa respectively. They are clearly homologous to the more highly organized blood-glands of the other Lumbriculid genera. They are peculiar in being extremely thin-walled and free from the covering of chloragogen cells. They project freely into the body-cavity when full of blood, and are almost invisible when empty. The dorsal vessel expands before the blind sacs. In tracing the ventral vessel backwards from the 13th segment, it is seen to give off occasionally a median dorsal branch, which enters the wall of the intestine. In the tail these vessels become much more numerous, 4-6 of them occurring in each segment. Just before entering the wall of the intestine, each vessel divides into two branches. The ventral vessel is slightly contractile behind. There are three transverse sections through one of the posterior segments. In No.1 the section passes through the dorsal vessel and one of the blind sacs. In No.2 it cuts both the blind sacs. This section also shows one of the branches passing from the ventral vessel into the wall of the intestine. In No.3 the section cuts the dorsal vessel and the obliquely lying sacs separately. There are slight indications are this point of a blood-sinus surrounding the gut. On passing from the tail towards the middle of the body this sinus becomes more prominent. About the middle of the body, the dorsal vessel appears only as the dorsal contractile portion of a perivisceral sinus which receives blood from the ventral vessel, and sends it forward in the dorsal vessel. This interpretation of the structure revealed by transverse sections is confirmed by examination of the living worms. In optical section the intestine shows a diffuse but distinct reddish tint, which is most strongly marked in the middle of the body, and which is evidently caused by the blood in the perivisceral sinus. The course of the blood is evidently as follows. In the anterior region it passes from the dorsal vessel through the commissures of the first 13 segments into the ventral vessel. In the latter it runs backwards, gradually passing through the median branches into the intestinal sinus. These branches, as already stated, are very numerous in the tail. Here they probably form a plexus round the intestine; and from this plexus alone the dorsal vessel is formed. There are no integumental vessels. Passing forwards the vessels of the plexus fuse to form a sinus round the intestine, and in open communication with the dorsal vessel. It is a debated point whether a plexus or sinus is present round the gut in the Oligochaeta, but in this case there seems to be no doubt that a sinus is present. That the dorsal vessel is fed from the intestinal sinus along the greater part of its length is also proved by the fact that when the worm is cut into two pieces at any part behind the clitellum, the dorsal vessel still continues to receive blood and the pulsate. In the family Lumbriculidae there is great variety of structure in the vascular system. There is no species, however, which at all resembles the one just described. The structure of the reproductive organs clearly proves that it belongs to the genus Stylodrilus. The restriction of the blind sacs to the tail and their simplicity of structure, considered in conjunction with the fact that they are quite absent in the other species of the genus, seem to show that they are undergoing a process of elimination. Taking into consideration the importance of the tail for purposes of respiration in these aquatic worms, it is natural that the blood-glands should be retained here when they have disappeared from other parts of the body. The new species thus forms an interesting link between the normal Lumbriculid type and the aberrant genus Stylodrilus. (ref. ID; 1928)

    Stylodrilus heringianus Claparede, 1862 (ref. ID; 1257, 1911, 3692, 7265) reported year? (ref. ID; 3704, 3955, 4491, 6607, 7817) reported author and year? (ref. ID; 5939)

    Synonym

    Stylodrilus gabretae Vejdovsky, 1882 (ref. ID; 1257); Stylodrilus vejdovskyi Benham, 1891 (ref. ID; 1257)

    Descriptions

    This species is indicative of oligotrophic condition. (ref. ID; 1911, 6607)

    Stylodrilus wahkeenensis Rodriguez & Coates, 1996 (ref. ID; 6651, 7265 original paper)

    Descriptions

    Refers only to mature specimens: Body consists of 33 or 34 segments. Body length is 5-6 mm. Body width is 0.32 mm in segment VIII, 0.30-0.35 mm at clitellum. Prostomium is very short and rounded, 51 µm long and 139 µm wide at the base. Clitellum is weakly developed, not raised, in VII-XI. Secondary annuli are present from the anterior part of V. Setae are two per bundle, single-pointed, with the nodulus in a markedly proximal position in both dorsal and ventral setae. The dorsal setae are thin, hairlike, and usually longer than the ventral ones. Dorsal setae are absent on II and III. In the anteclitellar segments, the dorsal setae are 117-180 µm long, 3 µm wide near the nodulus, the tip-nodulus/total length ratio is 0.7; the posterior dorsal setae are 100-206 µm long, 3 µm in diameter near the nodulus. The ventral setae on II and III are very large with curved tips, those on II being the largest (120 µm long, ca. 5 µm wide, the tip-nodulus/total length ratio is 0.6); in the holotype, ventral setae are missing on one side the body in II and III. Other preclitellar setae are 96-99 µm long, ca. 3 µm wide, the tip-nodulus/total length ratio is 0.6; the posterior ventral setae are 100-125 µm long, ca. 3 µm wide, the tip-nodulus/total length ratio is 0.6-0.7. The ventral setae appear to be bent in a characteristic way in the proximal region, probably providing a better mechanism for setal muscle attachment to the body wall. The ventral setae on X are present and unmodified. The spermathecal pores are paired, posterior to and in line with the ventral setae on VIII. The male pores are paired, posterior to and in line with the ventral setae on IX. Female pores are located in intersegment XI/XII. In the anterior segments, the body wall is formed by an epidermis encrusted with foreign material, 6 µm thick, with a circular muscle layer ca. 3 µm thick and a longitudinal muscle layer 19-29 µm thick. In the clitellum, the epidermis thickens to 11 µm. Pharyngeal glands are present in III-VI. Blind posterior lateral blood vessels are absent. The first nephridia are observed in VII. The sperm sacs extend anteriorly to VII and posteriorly to X. The egg sac extends posteriorly to XI or XIII. Paired testes are present in VIII and IX. The ovaries are paired in X. One pair of ciliated female funnels is situated on the septum X/XI. Two pairs of sperm funnels, located on septa VIII/IX and IX/X, join two pairs of vasa deferentia. The posterior vas deferens does not form a loop into the postatrial segment, but it is not clear whether it penetrates the ovarian segment slightly. Vasa deferentia 13 µm diameter, join the atria medially. Atria are present in IX, tubular (104 µm long, 45 µm in maximum diameter), the wall consisting of one layer of muscle fibres, less than 3 µm thick and with an internal epidermis 13-20 µm high, leaving a narrow atrial lumen. Prostate gland cells completely cover the atria, up to 24 µm thick. The atria opens to the exterior through a simple pore, indicated by strongly stained cells. An ejaculatory duct and penis are absent. One pair of spermathecae is located in VIII. Voluminous, saclike ampullae are present, one extending forwards to VII and the other backwards to X (260 µm in maximum diameter). A long spermathecal duct, 206 µm long and 32 µm in diameter, is clearly separated from the ampulla, the distal part being slightly enlarged near the pore (50 µm diameter). (ref. ID; 7265)

    Remarks

    The immature specimens have provisionally been ascribed to S. wahkeenensis because of the characteristic form of the dorsal and ventral setae; however, there are several differences in the chaetotaxy. In the individual from Litle River, the dorsal and ventral setae start on III, and the anterior ventral setae are neither enlarged nor curved at the distal end. The immature individual from Hendrick Mill lacks dorsal setae on II and the anterior ventral setae are present only on one side of II and III, with the remaining setae at the other side of the body as in the holotype. (ref. ID; 7265)

    Etymology

    The name of the species refers to the type locality. (ref. ID; 7265)

    Type locality

    Hyporheic waters in Wahkeena Creek, Oregon, U.S.A., 45 degrees 34'N, 122 degrees 07'W. Collected by E.L. Bousfield. (ref. ID; 7265)

    Type material

  • Holotype: ROMIZ I3185, stained with borax carmine and whole-mounted in Canada balsam. (ref. ID; 7265)
  • Paratype: ROMIZ I3186, one dissected mature specimen, stained and mounted as holotype, from type locality. (ref. ID; 7265)
  • Other material: One immature specimen mounted in Canada balsam, ROMIZ I3237, and two fragments mounted in CMC, ROMIZ I3238, from Hendrick Mill, northern Alabama, U.S.A., 33 degrees 52'12"N, 86 degrees 33'57"W, collected by D. Strayer, 4 October 1990. One immature worm mounted in CMC, ROMIZ I3307, from Little River, Tennessee, U.S.A., 35 degrees 39'55"N, 83 degrees 34'55"W, collected by D. Strayer, 1-2 October 1990. (ref. ID; 7265)