Dichogaster sp. A

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 : 141-142

Dichogaster sp. A

Material. USNM 1180245 , clitellate head fragment, Falaise de Véra , Gamba Complex, Gabon on forested hillside at 2.84873°S, 10.23569°E, 22 m asl., 16 May 2008; S. James, G. Divina, G. Moussavou and L. Tchignoumba, colls .

Description. Dimensions> 10 mm by 1.8 mm at segment X, 2.3 mm at clitellum, 1.7 mm at XXX; body cylindrical throughout. Setae closely paired throughout; setal formula AA:AB:BC:CD = 5:1:5:1.3 at X, 5:1:5:1 at XXX, DD> 1/2 circumference throughout. Prostomium proepilobous with faint single mid-dorsal furrow not quite reaching 1/2, no secondary annulation. Unpigmented except for very faint brown color along the mid-dorsal line, first dorsal pore 5/6, spermathecal pores paired 7/8/ 9 in AB. Paired ovipores nearly equatorial just median to A 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. Clitellum XIII–XIX, no genital markings.

Septa 5/6–8/9 very thin, membranous; 9/10–12/13 slightly muscular. Alimentary canal with two gizzards in V, VI; separated by thin annulus; paired calciferous glands in XV–XVII, reniform with internal lamellar structure; glands with separate ducts to esophagus wall, but close together; esophagus valvular in XVIII, intestinal origin XIX; typhlosole originating at 23/24; with closely spaced paired vertical flaps, height less than one fourth lumen diameter. No lateral typhlosoles. 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 above D.

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

Ovaries, funnels free in XIII; paired spermathecae in VIII, IX, each ampulla with slight constriction in the middle giving an hourglass shape, bilobed shortly stalked iridescent diverticulum attached near ampulla-duct junction; short muscular duct.

Male sexual system holandric, testes, funnels free in X, XI; seminal vesicles lacking; vasa deferentia superficial, muscular, enter body wall in XVIII; tubular prostates XVII, XIX in one or two short kinks, confined to segments of origin; long slender muscular ducts; penial setal follicles joined to body wall by long dorsal muscle band reaching to halfway between mid-lateral and mid-dorsal. Penial setae 1.15–1.23 mm by 11 µm in basal two thirds, tapering to 5 µm in distal third, in which the seta is unornamented over 4 complete undulations of low amplitude, finally tapering to a very fine point bent 90° from main axis.

Remarks. There is also a tail fragment of dimensions consistent with the head fragment, and having the same typhlosole structure in the anterior portion. If this is from the same species, then we can add that the typhlosole undergoes a gradual transition to a simple fold, and eventually terminates near segment LXXXV. The total body length would be roughly 35 mm. This worm was found on a decomposing tree trunk. It has the undulating penial setal structure, a typhlosole with vertical flaps, bi-chambered ampullae and first dorsal pores in 5/6.