Torodrilus
Torodrilus Cook, 1970 (ref. ID; 7798 original paper)
ref. ID; 7798
Definition
Hair setae absent. Modified genital setae present. Male and spermathecal pores paired, the latter situated close to the anterior intersegmental furrow of their segment. Vasa diferentia slightly longer than the atria, joining the latter apically to subapically. Atria elongate with a well developed muscle wall. Prostate glands in a compact mass, without a discrete prostatic duct. Spermatozeugmata not developed. Coelomocytes small and sparse, or absent. (ref. ID; 7798)
Etymology
"Torus" = L. muscle; "drilus" = worm. (ref. ID; 7798)
Type species
Torodrilus lowryi Cook, 1970 (ref. ID; 7798)
- Torodrilus lowryi Cook, 1970 (ref. ID; 7798 original paper)
Torodrilus lowryi Cook, 1970 (ref. ID; 7798 original paper)
Descriptions
Approximately 20 to 26 mm long, 0.40 to 0.63 mm in diameter, 62 to 94 segments. Prostomium rounded, longer than it is broad on the side which joins the peristomium, and with a small thin-walled papilla anteriorly. Clitellum well developed on segments IX to XII. Body wall, especially posteriorly, bears a number of very small transverse ridges (about 10 µm from crest to crest) in the furrows of which small substrate particles accumulate which appear to be bound together by external body secretions. (In the posterior part of the body this aggregation of material often peels from the body in narrow sttips which closely resemble branchiae on superficial examinaton.) Dorsal and ventral setae are similar in number, size and shape; anteriorly each bundle contains 4 to 6 bifid setae, 85 to 110 µm long; posteriorly each bundle contains 2 or 3 simple-pointed, or very faintly bifid setae with the upper teeth rudimentary, 80 to 90 µm long. Ventral setal bundles of segment IX each contain 1 large, modified spermathecal seta, about 240 µm long and between 8 to 24 µm thick. Spermathecal setae are thick proximally, become narrow in their central region, and are flattened into an elongated spoon-shape distally with rudimentary bifid apices. Ventral setae of segment X are unmodified by each ventral bundle of segment XI contain 2 thickened, round-ended penial setae, 140 to 180 µm long, 6.5 to 11 µm thick. A pair of very small spermathecal pores are located in the lateral line of intersegmental furrow IX/X. On the ventral surface of this furrow the body wall is folded to form a small mid-ventral papilla which bears a small pit on each lateral surface. Ventral surface of segment XI is deeply folded; the ventral-lateral part of the body wall, which is devoid of glandular (clitellar) epithelium, protrudes to form rounded conical structures resembling a pair of porophores; median to these are a pair of deep longitudinal folds which appear slit-like externally; the male pores open into the anterior part of these folds from the lateral side. Penial setae are inserted posterior and median to the male pores. Coelomocytes are few in number and only 6.5 to 8.5 µm in diameter. Pharyngeal glands are present in segment III to V. Septa 3/4 to 6/7 (especially 5/6 and 6/7) are greatly thickened by muscle fibers. Male genital system, (all structures paired); an inconspicuous male funnel, situated on the ventral part of septum X/XI, drains into a narrow vas deferens, 15 to 20 µm in diameter, which passes dorsally and joins the erect atrium more or less apically. Atrium cylindrical, with a conspicuous swelling apically (distally), 240 to 480 µm long, 90 to 140 µm in diameter distally, 44 to 51 µm in diameter proximally. Atrium consists of an outer muscle layer, 2.6 to 6.6 µm thick, and inner layer of lining cells which, towards the distal end of the atrium, is deeply folded longitudinal to the atrial axis. Atrium opens into the anterior part of the ventral body wall fold from the lateral side as a simple pore, without any modified penial apparatus. Proximal ends of the penial setae are ensheathed in tall vacuolated cells similar to those surrounding the spermathecal setae, described below. A large compact mass of prostate cell covers the anterior and dorsal parts of the atrium and the part of the vas deferens adjacent to the atrium. It is probable that the contents of the prostate cells drain into both the atrium and vas deferens. A number of short retractor muscles join the dorsal (distal) end of the atrium to the dorsal body wall. Long dorso-ventral retractor muscles also join the middle and posterior part of the ventral body wall folds of segment XI to the dorsal body wall. Masses of tissue resembling the prostate gland, but with no tracable connection with atrium or body wall, are present lateral to the dorso-ventral muscles. A pair of large spermathecae with very short indistinct ducts and ovoid ampullae (340 µm long, 250 µm wide in the holotype) are situated in segment X, and open into intersegmental furrow IX/X. Regularly spaced muscle fibres, which radiate from the proximal part of the ampullae near to the beginning of the duct junctions, surround the spermathecal ampullae and are arranged parallel to the latter's long axis. Spermatozeugmata are not developed but the sperm tails may be regularly oriented in discrete masses. The pair of large spermathecal setae, situated in segment IX, are sheathed and closely associated with a pair of discrete glands. Proximal part of each setal shaft is surrounded by a thick sheath composed of highly vacuolated cells, about 20 µm tall, and an outer tough muscular membrane. Robust and highly developed setal protractor and retractor muscles are inserted on the proximal end of this sheath. A discrete ovoid gland, about 130 µm long, 90 µm wide, with a duct about 45 µm long, opens to the exterior by a small pore situated very closely anterior to the insertion of each spermathecal seta. These glands appear to be simple invaginations of the body wall; the gland body is composed of a layer of tall collumnar non-vacuolated epithelium surrounding a narrow lumen, and the ducts consists of shorter, vacuolated epithelium resembling the cells of the sheath which surrounds the spermathecal setae. A single unpaired sperm sac extends backwards from septum X/XI. (ref. ID; 7798)
Remarks
The body wall of this species is often deeply furrowed, and small substrate particles tend to accumulate around it as in some species of Peloscolex. In the description it was pointed out that processes of the prostate cells probably penetrate both the atrium and vas deferens. Harbe (1967) stated that it is impossible for prostate cells to have any connection with the vas deferens because he had demonstrated (Hrabe 1939) that in some species of Tubificidae and Lumbriculidae the prostate cells are derived from outgrowths of atrial lining cells, which are ectodermal, and that their connective processes could, therefore, only penetrate the atrial wall. While this is probably true for the species he studied, the development of the male genitalia may be different in other groups. For example, a preliminary study of the morphogenesis of the genitalia of a species of Monopylephorus indicates that the atrium and prostate are of mesodermal origin (Cook, in preparations), in which case glandular tissue associated with both atrium and vas deferens would be expected to occur. The fact that Torodrilus lowryi has, a) few coelomocytes; b) no spermatophores and c) prostate glands which appear to be devoid of definite ducts or stalks, precludes this species from any of the subfamilies, and therefore genera, of Tubificidae described thus far. Inspection of Table I reveals that, on the basis of the three characters listed, Torodrilus lowryi is intermediate between the Rhyacodrilinae and the Phalodrilinae. It differs from the latter in its lack of prostatic ducts (compared, elongate processes of the prostatic cells entering the atrium at a specific point or area). In the Rhyacodrilinae the prostate gland consists of a diffuse layer of cells, each of which penetrates the atrial wall. While this seems to be the case in T. lowryi, the prostate gland is more compact and is located on a restricted area of the atrium and vas deferens. However, the lack of coelomocytes in T. lowryi precludes it from the Rhyacodrilinae as the latter is presently defined, but two facts suggest that the species may be related to this subfamily: 1) in the form and distribution of the genitalia and the genital setae it resembles Monopylephorus africanus Michaelsen, 1913 (it may be of significance that Michelsen (1913) in his account of this species failed to mention coelomocytes); 2) the distribution of the genitalia, the genital setae, the complex body wall folds and its associated musculature, and the glands associated with the spermathecal setae, are all very similar to those of Monopylephorus lacteus (Smith, 1900). On the other hand, the sparse coelomocytes of T. lowryi and its highly muscular atrium (as in Thalassodrilus Brinkhurst, 1963), suggest affinities with the Phallodrilinae. The author is reluctant to erect a new subfamily on the basis of a single species, yet does not wish to disrupt the present subfamilial classfication of the Tubificidae (Brinkhurst, 1970) by placing T. lowryi in an existing genus (either Thalassodrilus (Phallodrilinae) or Monopylephorus (Rhyacodrilinae), depending on the weight assigned to the genital or coelomocyte characters). Thus the species has been placed in a new monotypic genus to await future work on the morphology of the Tubificidae in relation to the value of the taxonomic characters now in use. (ref. ID; 7798)
Etymology
Species named for James K. Lowry who collected the type material. (ref. ID; 7798)
Distribution
Known only from the type locality. (ref. ID; 7798)
Type specimens
Holotype: United State National Museum (USNM) 40043. West side of Arthur Harbour, Anvers Island, Antactica, at 64 degrees 45'49"S, 64 degrees 05'51"W. Depth: 30 to 35 m. Substrate: approximately 70% silt, 25% clay, 5% sand. Sediment temperature: -1.8 to 0.0 degrees C. Salinity: 33 to 34 0/00. Collected by J.K. Lowry. (ref. ID; 7798)
Paratypes: USNM40044. 5 individuals (7 slides); data as for holotype. (ref. ID; 7798)