Dichogaster (Diplothecodrilus) tchignoumbai, James & Divina, 2012

James, Samuel W. & Divina, Gildas Brice, 2012, Earthworms (Clitellata: Acanthodrilidae, Almidae, Eudrilidae, Glossoscolecidae, Ocnerodrilidae) of the coastal region of Gamba, Ogooué-Maritime Province, southwestern Gabon, Zootaxa 3458, pp. 133-148 : 135

Dichogaster (Diplothecodrilus) tchignoumbai sp. nov.

( Figs 1C,D, 3B)

Material. Holotype USNM 1142294 , clitellate, near Vembo , Gamba Complex, Gabon in forested low area, 2.74693°S, 10.00476°E, 5 m asl., 18 May 2008; S. James, G. Divina, G. Moussavou and L. Tchignoumba, colls . Paratype USNM 1142295 : one clitellate, same data as holotype .

Etymology. The species is named for Landry Tchignoumba, one of the Gabon Biodiversity Program technicians who were part of the collecting team at Gamba.

Diagnosis. Dichogaster (Diplothecodrilus) with penial setae of one type, slightly bowed, gradually tapering to diameter of 2.5µm in distal third, in which the seta has several very slight scars spaced evenly on the shaft, with a barely perceptible bend at each scar, bends alternating in direction; end of seta blunt, the bifid typhlosole, mid-ventral oval genital markings with paired glandular spots presetal in XV, on 21/22/23/24/25 and spermathecae in VII and VIII with pores in 7/8/9.

Description. Dimensions 50, 51 mm by 2.5 mm at segment X, 3.0, 3.1 mm at clitellum, 2.1, 2.3 mm at XXX; body cylindrical throughout, segments 135+, 137+. Setae closely paired throughout; setal formula AA:AB:BC:CD = 4.5:1:3.5:1 at X, 8:1:6:1 at XXX, DD> 1/2 circumference throughout. Prostomium retracted into buccal cavity overhung by forward edge of peristomium, therefore schizolobous. Unpigmented, no secondary annulation. First dorsal pore 5/6, spermathecal pores paired 7/8/ 9 in B. Ovipore single mid-ventral in XIV; male pores in XVIII; prostatic pores and penial setae at ends of seminal grooves in AB in XVII–XIX. Seminal grooves slightly convex laterally; male field elevated. Clitellum XIII–XIX, saddle-shaped reaching to 1/2 BC in XIII–XV, to C in XVI–XIX; mid-ventral oval genital markings with paired glandular spots presetal in XV, on 21/22/23/24/25 ( Fig. 1C).

Septa 4/5–11/12 muscular. Alimentary canal with two gizzards in V, VI; separated by thin annulus; paired calciferous glands in XV–XVII, reniform with internal lamellar structure in XVI, XVII but apparently lacking this in XV; XV glands same size as XVI, XVI<XVII; glands with separate ducts to esophagus wall, but close together; esophagus valvular in XVIII, intestinal origin XIX; typhlosole a thin bifid fold with sparsely placed paired vertical flaps originating in XXIII, height less than one fourth lumen diameter, ending in LXXX, LXXXIX. Lateral typhlosoles XXIII, XXIV–XXXIII, XXXV. Nephridia of anterior segments small plectonephridia, 8 per segment; in intestinal segments stomate megameronephridia 1 per side near AB, 3 sac-like meronephridia per side from B to near mid-dorsal.

Vascular system with ventral trunk, single dorsal trunk, these connected by lateral trunks in VIII–IX, lateroesophageal hearts in X–XII. Extra-esophageal vessel not seen; supra-esophageal vessel X–XII.

Ovaries, funnels free in XIII; spermathecae two pairs in VIII (1 specimen) or VII, VIII, each a tongue-shaped ampulla with slight constriction in the middle, bilobed shortly stalked iridescent diverticulum attached near ampulla-duct junction; short muscular duct ( Fig. 1D) .

Male sexual system holandric, testes, funnels free in X, XI; in one specimen funnels of XI lacking iridescence; seminal vesicles in XI, XII (one specimen) or only XI (specimen with only funnels of X iridescent); vasa deferentia superficial, enter body wall in XVIII; tubular prostates XVII, XIX in tight zig-zag folds, confined to segments of origin; long slender muscular ducts. Penial setae 0.9 mm long, slightly bowed, gradually tapering to diameter of 2.5µm in distal third, in which the seta has several very slight scars spaced evenly on the shaft, with a barely perceptible bend at each scar, bends alternating in direction; end of seta blunt and fluted ( Fig. 3B).

Remarks. By the location of the first dorsal pore and the spermathecal ampulla’s constriction into two sections, this species belongs to the subgenus Dichogaster (Diplothecodrilus) . Within that subgenus Csuzdi (1996b) indicates six species-groups with a single type of penial setae and divides them according to the general form of the penial setae. The penial setae of D. tchignoumbai are similar to those of the affinis -group, and within this group it is most similar to D. toroensis Cognetti, 1907. Among the differences from D. torensis are the oval genital markings in XV and behind the clitellum, the bifid typhlosole, the thicker and much shorter spermathecal ducts, spermathecae in VII and VIII with pores in 7/8/9, and the penial setal morphology having fewer denticles and a rounded spatulate tip.