Phagodrilus

Phagodrilus McKey-Fender, 1988 (ref. ID; 6555 original paper)

Family Lumbriculidae (ref. ID; 6422, 6555)

ref. ID; 6555

Diagnosis

Prostomium rostrate. Mouth very broad. Setae single-pointed, sigmoid; postclitellar dorsal pairs are crotchets. Male pores one pair ventrally, postsetal on X. No penes. Ovipores one pair ventrally in furrow 11/12. Spermathecal pores one pair postsetal ventrally on IX. Anterior end of body, including pharygeo-esophageal region of alimentary canal (segments II-IX), forming a suctorial organ with muscular wall and cuticular lining; coelom obliterated in segments II to posterior third of IX by muscle tissue. Lumen of pharynx triangular, the apex dorsad. Pharynx in posterior third of segment IX circular in corss section, free from parietes, and with greatly thickened musculature, forming a strong sphincter. Two pairs of lateral segmental vessels in each midbody segment; vessels much branched; branches that attain parietes having caecal appendages that nearly fill coelom. Testes paired ventrally from septum 9/10 in X. One pair of functional sperm funnels and ducts in X, with ducts leading to paired atria in X. Functionless large to miniscule funnles in IX. Sperm ducts contacting atria at base but opening distally. Atria simple, with uniform continuous glandular prostatic investment. Ovaries paired ventrally in XI. Ovifunnels paired on septum 11/12 with short ducts opening in furrow 11/12. Paired ovisacs extending back from 11/12, containing the sperm sacs in their anterior portions. Paired spermathecae in IX with very elongate ducts originating within occluded portion of that segment; ampullae enclosed in sacs formed from septum 9/10 (sperm sacs of IX) drawn back into sacs of X. Sperm sacs and ovisacs are paired and extend backward through many segments from their origin. (ref. ID; 6555)

Etymology

Phago from Greek phagein, to eat; and drilus from Greek drilos (masculine gender), penis, hence a worm. (ref. ID; 6555)

Type species

Phagodrilus macnabi McKey-Fender, 1988 (ref. ID; 6555)

Phagodrilus macnabi McKey-Fender, 1988 (ref. ID; 6555 original paper)

Phagodrilus macnabi McKey-Fender, 1988 (ref. ID; 6555 original paper)

Descriptions

Large, length 164-280 mm, width 3-5 mm, segments 193-244. Prolobic, prostomium rostrate, elongate, length/width 1.5, digitiform in extension, forming annuli in contraction, limited posteriodorsally by a groove (groove V-shaped in extension). Peristomium swollen, furrow 1/2 somewhat constricting segment I from the following, pharyngeal portion of the forebody. Form moderately slender, smoothly cylindrical anteriorly, especially anterior to X (pharyngeal segments). Anterior segments differentiated in color, paler. Primary annulation obscured anterior to X, in pharyngeal region, which is finely multiannulate. Evident annulation, primary and secondarry, beginning in X, but obscured by clitellum (X-XV) at sexual maturity. Segment II short, III longer, IV to VIII very long, IX longest, about twice length of those following, X short, postclitellar segments about equalling III. Secondary multiannulate with true segmentation evident externally with difficulty by location of the setae. Unpigmented, in life flesh-pink anteriorly, pharyngeal portion uniformly creamy with red blood vessels showing through; midportion of body behind pharynx red-brown from contained chloragogen; cuticle irdiescent. Body wall translucent. Clitellum cingulate, in life evidenced by a whitish, glandular bloom; on X-XV. Soma dorsally flattened posteriorly; caudal soma wide and flat, especially on dorsum, rounded ventrally, width/depth 1.5 to 2.16. Anus dorsoterminal. Spermathecal pores small round pits postsetal on IX in line AB, in a transverse glandular area in the sexually most developed specimens. Spermathecal ducts often subepidermally visible externally. Male pores paired in line AB, in a narrow, transversely elongate field, width/length 2.3 to 4.9, anterior and posterior margins of field thickened, a pit-like depression anterior to each atriopore (appearing much like the pore). Nephropores must anterior to ventral setal pairs, first apparent on XIII, not invariably present in every segment; somewhat tumid but very small, located ab to 2ab distance anterior to b. Setae eight per segment, closely paired, AA:AB:BC:CD=14:2:21:3, DD=1/8C. Ventral and anterior dorsal setae slender, sigmoid, and with apices only gently curved; dorsal pairs of postclitellar setae stouter, more strongly curved and with hooked (uncinate) apices, i.e., crotchets. Postclitellar dorsal setae strongly, evenly curved, apical hook moderately open, tip directed proximally into basal third of distal part of shaft, distal part of seta above nodulus 43% of total length of seta. Length 481 µm, diameter 28 µm. Setae present on all except segment I and last one or two segments, located at or near posterior third of segment. Lateral line visible. Septa in pharyngeal region lacking; present from 9/10. Mouth large and wide, equalling the entire diameter of the body and further greatly expandable. Buccal cavity simple. Coelom of segment I not concluded by muscle as are the pharyngeal segments. Entire anterior end of animal except segment I constitutes the suctorial pharynx; coelom, obliterated in these segments, except as narrow channels along the nerve cord and blood vessels, otherwise solidly filled with muscle tissue; solid portion of muscular pharynx extending to posterior segment IX, an unusually long segment; posterior, funnel-shaped portion of pharynx extending from this point in IX to 9/10, muscularly thickened, gizzard-like, round in cross section. Pharyngeal valve at 9/10, consisting of about 6 glandular lobes or flaps, closing pharynx off from intestine. Lumen of pharyngeal portion lined with heavy cuticle. Lumen triangular in cross section with the apex of the triangle dorsad. Wall at angles of lumen very much thinner than in between, less than one-third thickness of sides of triangle in a state of moderate contraction; epithelium glandular at angles, forming longitudinal impressed grooves; these less pronounced in the funnel-shaped portion in IX. Intestine undifferentiated, lined throughout with a thick layer of glandular folds, these short rugae or villi more or less uniformly transversely oriented; intestine dorsoventrally flattened to about segment XV, becoming nearly round and very slightly moniliform. Diameter of intestine very much narrower and again flattened toward the posterior end. Intestine clothed externally, especially midbody, by a heavy chloragogen layer. Spermathecae one pair, in front of the testis segment; large, ovate, length/width 3, ampulla sharply set off from the exteremly slender, somewhat convoluted ducts; originating in segment IX a short distance behind the ventral setae; ducts extending back through solid pharyngeal tissue of IX subepidermally, visible externally in favorable material, into the coelom of posterior part of segment IX; thence carried back within the paired "spermathecal" sacs to the level of about XI-XIII. The sacs postseptal from 9/10 are presumably the sperm sacs of IX and are similar to the sperm sacs of X and the ovisacs of XI and are enclosed within them. Ampullae distended with sperm in spring (March-June) specimens. Paired testes and atria in segment X. Testes paired postseptal ventrally from 9/10, consisting of irregular, somewhat flattened lobes. No testis tissue has been found in IX. Functional sperm funnels in coelomic cavity of X but carried back into mouths of the sperm sacs where they are recognizable as iridescent patches on anterior surface of septum 10/11. Functional vasa efferentia follow 10/11 preseptal ventrally to floor of segment X and thence anteriorly to bases of atria. Each becomes adherent to the wall of the corresponding atrium under the prostatic cells of the atrium and passes thus to halfway up atrium where it appears to enter, though it actually opens into lumen near the atrial apex. Anterior, nonfunctional efferentia and funnels present, funnels reduced to narrow, barely visible thickenings of septum 9/10. Efferentia of IX more slender than those of X but traceable similarly on floor of anterior X and on anterior face of atrium. Atria short, ellipsoid, length/width 2.3 to 3.75. Prostatic investment of atria continuous, of uniform thickness, smooth. Functional sperm sacs (seminal vesicles) simple outpouchings of septum 10/11, lying alongside and above intestine, extending posteriorly to at least XIII, filled with coagulum posteriorly and containing the spermathecae within the sacs of 9/10 and themselves contained within the ovisacs. Ovisacs originating similarly as invaginations of septum 11/12 and extending several segments behind the sperm sacs; containing the large eggs in their posteriormost portions, together with a coagulum that turns brown on fixation (Bouin's). All sacs are membranous, nonglandular. Ovaries paired ventrally, postseptal from 10/11; simple, flattened lobes usually somewhat curved distally, forming a broad, C-shaped or J-shaped mass, narrower basally. Ovifunnels paired ventrally in line AB, simple, small, not equalling one-third of AB to BC distance. In a number of worms, the genital organs of one side were more strongly developed than the other. First nephridia in XIII, with preseptal funnels on 12/13, mediad from AB. There are no astomate or other wise reduced nephridia anteriorly. Nepharidia are not invariably present on both sides of each segment but as least one is present in each segment behind XII, distribution apparently without pattern. The highest number present consecutively was 13. Nephridia consist of a preseptal funnel which is flattened, having a broader dorsal and a narrower ventral lip, a prespetal portion of the nephridial duct about as long as the funnel, followed postseptally by a short, narrow portion of the duct which soon widens to form a sac-like glandular part; this part gives off two branches, one extending posterolaterally to the nephropore just in front of setal bundle ab, the other passing medially, becoming convoluted, and lying on the dorsal surface of the ventral vesel, close beneath the intestine and close beside the corresponding tubule of the nephridium of the other side where present; this branch extending posteriorly nearly or all the way to septum; communication through the septum with ducts of the next posterior segment has been demonstrated in some anterior segments at least, while communication laterally between right and left ducts of the same segment has not yet been demonstrated; ducts connected dorsally by several fine connections distributed at intervals along their length to the ventral surface of the intestine, which lies closely above. Ventrally the nephridial ducts are closely connected to the ventral vessel, but here again relationships are not clear; connections to the ventral vessel are less firm than the abovementioned connections to the intestine. The neck of the sack-like portion may be darkened by waste material, the remainder of the nephridium appearing whitish. All of the specimens examined for this feature had the anteriormost nephridia in XIII with preseptal funnels in XII. No nephridia have been observed in the last several segments. Musculature strongly developed throughout the body, especially in pharyngeal region. Coelom of segments II to posterior third of IX solidly filled with muscle tissue except for the narrow channels containing blood vessels and nerve cord. Circular muscle layer of this portion relatively thin, discontinuous, arranged in narrow, compact rings, 1/10 to 1/15 thickness of the thickest portion of the wall; circular muscle layer behind the pharyngeal region similarly, though increasingly less definitely, arranged in rings. Remainder of pharyngeal wall an intricate system of longitudinal and radial muscle bands. Longitudinal bands very thin, flat, and ribbon-like filling the pharyngeal parietes radially within the epidermal and circular muscle layer and extending longitudinally the full length of the pharyngeal region; individual ribbons traceable from their posterior origins in the funnle-shaped portion of the pharynx to the posterior portion of the buccal cavity where they become confused, appearing to be interlaced with muscles of the circumoral parietes. Radial muscle in similar, short strips between the circular muscle rings described above and the pharyngeal line. Longitudinal musculature of parietes of segments X-XIII in seven separate bands; at XIV these are subdivided into about 12, these further subdivided some segments farther posteriorly and so on. In the posterior part of the body in P. macnabi there are 20 separate bands. The anterior nervous system consists of the suprapharyngeal ganglion ("brain") dorsally in segment I; two pairs of nerves (pn) extending anteriorly into the prostomium, the paired recurrent nerves (r) extending from posterior margin of the brain posteriad to the roof of the mouth. Subpharyngeal ganglion ventral in II, paired nerves (mn) extending to floor of mouth. Nerve cord in anterior segments of very uniform diameter, no ganglionic enlargements visible externally. Most of the following details of the circulatory system were obtained from living material. In the pharyngeal region, beginning in III, there are paired segmental, slender commissural vessels between dorsal and ventral vessels. These vessels are not contractile and are long, wandering through a much-contorted path between the two trunks, allowing for extension and contraction of the anterior segments. Corresponding right and left commissures neither branch from the dorsal vessel nor join the ventral vessel directly oppoiste one another. Begining in vicinity of XVI-XVIII and in each segment thererafter, there are two paired lateral vessels between dorsal vessel and ventrolateral surface of intestine; these are extensively dendritically branched on the side facing the parietes, most branches attaining patrietes between the muscle bands where they penetrate nearly to the surface and extend longitudinally along the breaks between muscle bands. These longitudinally oriented vessels are externally visible in the parietes close to the surface of the body. They are not trunks. Each of the pariental branches of these lateral vessels sends a number of blind (caecal) vessels (cv) back into the coelom; in segment XXXV midlaterally there are about nine such caeca per segment in each row. The number of caecal vessels is largest midbody, where the coelom is nearly filled such vessels and the branched dorsointestinals from which they originate. The coelomic portions of these vessels as well as the dorsal vessel (d) and intestine (i) are thickly covered with chloragogen, adding to the coelomic occlusion. The pattern extends throughout the body, but in the posterior third the chloragogen lessens and in the anterior part of the body, anterior to about XX to XXV, it is also thinner. The vascularization of segment XXXV seems to be typical of most of the posterior soma. Two ventral medial intestinals between ventral vessel and intestine in each segment. Dorsal vessel with a large cardiac body. The dorsal vessel forks in segment II, sending a long loop on either side into the coelom of segments I halfway down toward the ventrum and up to again, out into the prostomium where each loop turns back on itself and passes under the aforementioned loops deep in the tissue of the peristomium, uniting ventrally at the anterior limit of segment II to form the ventral vessel. Subneural or other additional longitudinal trunks absent. This is a large, robust, flat-tailed species with short atrium and broad spermathecal ampulla. (ref. ID; 6555)

Comparison with Agriodrilus vermivorus Michaelsen, 1905

We have compared Phagodrilus with both published descriptions and specimens of A. vermivorus and have found the following similarities and differences. Both A. vermivorus and Phagodrilus are multiannular. The pharygeal region has a similar overall look and is similarly constructed in that abundant muscle fibers radiate to the body wall, totally occluding the coelom. This occluded pharyngeal region is easily discernible externally in both taxa. However, although the lumen of the pharynx is triangluar in cross section in both genera, the apex is directed dorsal in Phagodrilus, ventrad in A. vermivorus. The posterior end of the pharynx of A. vermivorus lacks the gizzard-like muscular funnel found in Phagodrilus. These features suggest a basic difference between the pharynges of the two animals, implying an origin from a different sort of pharynx in the two cases, the overall similarity being due to the identical function. Agriodrilus vermivorus is described as having the anterior end filled with "mesenchyme" cells derived from the coelomic epithelium (Michaelsen 1926; Chekanovskaya 1962; Cook 1971), but the dominant costituent of this region appears to us to be muscle as in Phagodrilus, though there may be differentiated cells among the abundant muscule fibers. As is common to many Lumbriculidae, both A. vermivorus and P. macnabi possess blind "caecal" branches to the lateral branches of the vascular system. In Phagodrilus these become conspicuous by segment XVIII and are develped primarily from branches of lateral vessels after they have reached by body wall. The caecal vessels are produced in very regular rows from within the gaps in the longitudinal musculature. Blind vessels in A. vermivorus are similarly produced from vessels that have reached the parietes (Chekanovskaya 1962), but are randomly arrayed on the body wall, rather than organized into gaps in the longitudinal musculature (personal observation). The circular muscle is organized in a nearly solid sheet, as opposed to the discrete rings in both Phagodrilus and certain Stylodrilus (Bythonomus) species. The setae of A. vermivorus are nearly straight, whereas the dorsal setae of Phagodrilus are hooked, and even the ventral and anterior setae are moderately strongly curved. The gonads in Phagodrilus lie one segment anterior to their location in A. vermivorus (in X and XI in Phagodrilus; in XI and XII in A. vermivorus). More importantly, perhaps, the spermathecae are anterior to the gonads (in segment IX) in Phagodrilus, whereas they are posterior to the gonads (in segment XIII) in A. vermivorus. Also, there are no penes in Phagodrilus, whereas well-develped penes are present in A. vermivorus. (ref. ID; 6555)

Etymology

Named in honor of James Arthur Macnab (1899-1985), teacher, co-worker on the oligochaetes, and friend, who collected the first specimens of this genus in the Coos Bay, Oregon are in 1949 and who retained a lifelong interest in these fascinating annelids. (ref. ID; 6555)

Type slide

Holotype: OREGON: Coos County, Chareleston, Oregon Insitute of Marine Biology, T25S R14W Sec. 2, 10 April 1985, No.1 spring-fed swamp among Picea sitchensis, Alnus rubra, Rhododendron macrophyllum, Myrica carifornica (with Phagodrilus sp.), WMF and DMF. (ref. ID; 6555)