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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Metataxis

Metataxis Righi, 1985 (ref. ID; 6578) or Righi, 1985 emm. Omodeo, 1987 (ref. ID; 6421)

Family Enchytraeidae: Subfamily Achaetinae (ref. ID; 5790)

Family Haplotaxidae (ref. ID; 5813, 6578)

Synonym Pelodrilus, partim (P. americanus Cernosvitov, 1939; P. falcifer Omodeo, 1958) (ref. ID; 6578), Haplotaxis, partim (H. brinkhursti Cook, 1975) (ref. ID; 6578)

ref. ID; 6421

The genus shares the lumbricine arrangement of gonads, and shows relationships with the Syngenodrilidae and Alluroididae, both of which share the plesiomorphic condition of large yolky eggs and ample egg sacs, as well as the sparganophilid Neotropical Areco, according to Omodeo (1987). It seems better to recognize this relationship rather than to include the genus in the Haplotaxidae. It only required a slight weighting of character 3 (loss of GIII) to shift all of the included species to an outgroup status vis-a-vis the Haplotaxidae. (ref. ID; 6421)

Type species

Type species by designation Metataxis eliae Righi, 1985 (ref. ID; 6421)

ref. ID; 6578

In his revision of the Haplotaxidae, Brinkhurst (1966) regarded as "species inquirendae" Pelodrilus americanus Cernosvitov, 1939 and Pelodrilus falcifer Omodeo, 1958 because their lumbricine gonadial arrangement (holandric, opisthogynous) differed from other haplotaxids, but they were considered to be only partially mature - the male pores of P. americanus were not located, for example, and the male ducts may not be plesioporous. Righi (1985) described the new taxon Metataxis eliae from Venezuela, and transferred not only P. americanus (Peru) and P. falcifer (Africa) to the genus but also Haplotaxis brinkhursti Cook, 1975 (North America). These species are holandric and opisthogynous with paired spermathecae with dorsolateral to dorsal pores, but P. falcifer has testes in XI only and one dorsal median spermatheca and maybe more. A second African species, described below very closely resembles M. falcifer in these respects except that there are three mid-dorsal spermathecae in VII-IX. These two African species may differ at the subgeneric level from the American species. (ref. ID; 6578)
  1. Metataxis americanus (Cernosvitov, 1939) (ref. ID; 5813) reported author and year? (ref. ID; 6421)
  2. Metataxis brinkhursti (Cook, 1915) (ref. ID; 5813) reported author and year? (ref. ID; 5790, 6421)
  3. Metataxis carnivorus Omodeo, 1987 (ref. ID; 6578 original paper) reported author and year? (ref. ID; 6421)
    Syn; Pelodrils carnivorus, nomen nudum, Omodeo, 1958 (ref. ID; 6578)
  4. Metataxis eliae Righi, 1985 (ref. ID; 6421)
  5. Metataxis falcifer (Omodeo, 1958) (ref. ID; 5813) reported year? (ref. ID; 6421)

Metataxis carnivorus Omodeo, 1987 (ref. ID; 6578 original paper) reported author and year? (ref. ID; 6421)

Synonym

Pelodrils carnivorus, nomen nudum, Omodeo, 1958 (ref. ID; 6578)

Descriptions

  • External morphology: Body slender, slightly prismatic, caudal end club-shaped; the adult specimens are 56 and 58 mm long and 0.8 mm thick (1 mm at the cilitellum). Segments without evident secondary annulation to about 120. No cutaneous pigment, body wall transparent. Prostomium zygolobous, semicircular. The cuticle is 2.5 µm thick. No dorsal pores; nephridial pores perhaps on the lateral line. Male and females pores not perceptible by external inspection, but paired at 11/12 and 12/13 respectively, near the setal line ab. Three spermathecal pores along the middle dorsal line at 6/7, 7/8, 8/9. Two pairs of ventral setae on all segments (peristomium excepted), the dorsal setae disappear from XL onward. The setae are drawn Fig.4E; their length is at X (from a to d): 230, 170, 130, 170 µm, and at XXXVII: 165, 125, 105, 135 µm. Ventral setae have near the tip some crescent-shaped incisures, dorsal setae are smooth. (ref. ID; 6578)
  • Internal organization: No gizzard, no typhlosole, no calciferous glands; septal glands in IV, V. Septa thin, the anterior ones funnel-shaped. Circulatory apparatus greatly developed in the cephalic segments; in each segment from I to XIII there are paired convoluted transverse commissures connecting the dorsal and the ventral vessel. These commissures are similar to those of Haplotaxis villiersi but their form is altered by the extrusion of the pharynx; in the following segments commissures are straight. Cerebral ganglia between pro- and peristomium. Holonephridia begin in XVI or XVII, they are covered by vesicular peritoneal cells. The setae ab of XI-XV are implanted in small glandular pads. There is a single pair of testes situated in the fore part of XI and a single pair of seminal vesicles derived from XI-XII, which penetrates the ovarian sacs, filling them almost completely. Ciliated seminiferous funnels are situated in the ventral lip of sperm sacs. There is a single pair of ovaries in the front part of XIII followed by a pair of long ovarian sacs derived from XIII-XIV. The left ovarian sac in the dissected adult specimen reaches XXVI, and the right one reaches XXX. The bigger ovarian eggs measure about 250x170x100 µm, the eggs contained in the bottom of ovarian sacs, rich in yolk, are spherical with a diameter of 350 µm and are yellow in color. Female funnels were not observed. In a young specimen there was a pair of rudimentary gonads (ovotestis?) in XII. The unpaired spermathecal pores open in 6/7 - 8/9 along the dorso-median line: the duct is short with thin walls, the ampulla is pyriform, transversely enlarged. The anterior spermatheca is bilobed and smaller, the posterior is bigger, they no longer contain sperms, in adult specimens. (ref. ID; 6578)

    Remarks

    The gut content of these oligochaetes is the same as that of Villiersia guanivora, but in the pharynx of one specimen there was a large fragment of an insect larva having thin hispid cuticlebearing minute, arched bristles; the muscle tissue, partly decomposed, was transversely striated. I did not observe any plant fragment, thus the worm must be guanivorous and occasionally carnivorous: its specific name derived from such a characteristic. (ref. ID; 6578)

    Systematic relationship

    Metataxis carnivorus resembles M. falcifer, especially because of the unpaired mid-dorsal spermathecae. For this peculiarity both African species differ from the congeneric American species which are like the genera Alluroides and Brinkhurstia belonging to the fam. Alluroididae. The gonad distribution resembels that of Styloscolex (Lumbriculidae). (ref. ID; 6578)

    Type locality

    Guinea, Segea caves near Kindia, in a brooklet in the dark halls; water temperature 26 degrees C, pH 5.0. Dr. A. Villiers leg. April 7, 1954; 28 'softened' specimens, two of which are adult. (ref. ID; 6578)