Dichogaster spolstoni

James, Samuel W. & Gamiette, Franciane, 2016, New species of Dichogaster Beddard, 1888 (Clitellata: Benhamiidae) with additional records of earthworms from Guadeloupe (French West Indies), Zootaxa 4178 (3), pp. 391-408 : 392-394

Dichogaster spolstoni . n. sp.

( Figure 1 A–D)

Holotype. MNHN HEL 590 adult, Faux Pitons Bouillantes trail in montane forest soil, Basse Terre, Guadeloupe, N16°07.943', W61°43.636', 1018 m asl.

Paratypes. MNHN HEL591, 2 clitellate adults from type locality.

Etymology. Making an anagram from the words “Pitons” and “sol” one of the possibilities is spolstoni , the name we give to this species.

Description. Dimensions 64–66 mm by 2.5–3.0 mm at segment x, 3–3.5 mm at clitellum, 3.0 mm at xxx; body cylindrical throughout, segments 150–179 (3 individuals). Setae all ventral, closely paired throughout; setal formula AA:AB:BC:CD = 4:1:5:1 at xxx; DD> ½ circumference. Prostomium schizolobous, completely divided by a single mid-dorsal groove; segments with pre- and post-setal secondary annulations in posterior half of body. Burgundy pigmentation present dorsally in pre-clitellar segments with faint mid-dorsal band of pigment elsewhere, overall posterior color tan to olive in formalin preservation. First dorsal pore 11/12, spermathecal pores deep in 7/8, 8/ 9 in A. Ovipores equatorial just median to A in xiv on elevated area; male pores in xviii; prostatic pores and penial setae at ends of grooves in A in xvii–xix; grooves straight, surrounded by raised field with transverse bar papillae on xvii, xix. Clitellum xiii–xxi, saddle-shaped reaching to ½ BC, no other genital markings ( Fig. 1 A–C).

Septa 5/6–8/9 membranous, 9/10–13/14 slightly muscular, 9/10 and 10/11 fused at body wall margins. Alimentary canal with proventriculus in v, two long gizzards in vi, vii; esophagus valvular in xviii, intestinal origin xix; deeply sacculated xix–xxx; typhlosole a simple fold originating in region 22/23–23/24, height one quarter lumen diameter, with vertical folds through xxx, continuous lateral typhlosoles xxiv–xxxii, typhlosole ends cxxvii, cxxxvii. Calciferous glands reniform, paired in xv–xvii, composed of longitudinally-oriented lamellae opening to medial lumen; each gland with separate duct to esophagus, glands of xv equal in size to those of xvi, these smaller than glands in xvii; glands of xvii have 3 to 5 indentations of the lateral margins. Meronephridia 12 per segment, pre-intestinal nephridia tubular; intestinal segment nephridia closed sac-shaped with oil droplets; ventralmost rows of posterior segments with nephrostomes; no nephrostomes seen anteriorly; nephridia distributed AB-dorsum. Vascular system with ventral trunk, single dorsal trunk, these connected by commisural vessels in v (?), vii, viii, ix, latero-esophageal hearts in x–xii, increasing in size posteriorly. Commissural vessel of vii to gizzard wall only.

Fan-shaped ovaries composed of long strings, with funnels in xiii; paired spermathecae in viii, ix, each a roughly conical ampulla with bilobed stalked diverticulum; one lobe always larger than the other ( Fig. 1 D). Male sexual system holandric, testes and funnels in ventral paired sacs in x, these sacs extending anteriorly under gizzard; testes and funnels free in xi; acinous equal-sized small seminal vesicles in xi, xii; tubular prostates with very short delicate ducts, sharply marked from narrow tubular glandular portion; glands in many zig-zag folds within segments of origin or extending into next segment posterior; glands of xvii much larger; penial setal follicles and penial setae very small, vestigial, just median to ducts.

Remarks. This species was found in the highly organic soil of a short-stature montane forest, not in suspended soil habitats. Dichogaster caesiticifusca James, 1996 was also found in the soil, and Dichogaster callaina James, 1996 and Dichogaster sp. 2 (see below) were found in bromeliads of the same area.

First we will review what distinguishes Guadeloupe Dichogaster (Dichogaster) species from their sub-genus congeners in Africa and the Neotropics. Some of this, including the status of Eutrigaster Cognetti, 1904, and species assigned to Eutrigaster in Sims (1987) was discussed at length in James (1996, 2004). By specifying the prostates in xvii and xix, spermathecae in viii and ix, gizzards in vi and vii, seminal grooves present, and caeca absent, one eliminates most Neotropical species. Restricting to the same character states plus first dorsal pore near 11/12 +/- a segment or two, most African species (dorsal pores more anterior, near 5/6) are eliminated from consideration. Further reductions of the African species are accomplished by specifying that penial setae are either absent or monomorphic (only one morphological type per bundle), and by restriction of the remaining to those of a particular spermathecal morphological category, in this case the damonis -group sensu Csuzdi (2010). This group is characterized by having non-muscular spermathecal ducts with a stalked diverticulum arising from the duct. Thus one arrives at a direct comparison with some neotropical species: D. gagzoi Michaelsen, 1908 , D. picadoi Michaelsen, 1912 , and D. altissima James, 2004 . Of these the ones with the same number of nephridia in the intestinal segments (10) are the latter two. Dichogaster picadoi differs by having longer and more developed lateral typhlosoles than D. spolstoni and other Guadelope species, while D. altissima has a more complex typhlosole with vertical flaps, greater septal muscularity in degree and segmental extent, nephridia on the muscular septa, and different fusion of segments in the male gonadal region: 10/11/12 rather than 9/10/11. These differences also apply to all Guadeloupe Dichogaster (Dichogaster) species.

Turning now to the previously-known species from Guadeloupe, in James (1996) there are four acaecate species, and all are obviously pigmented, either blue-green or red to red-brown. The acaecate Guadeloupean species of the same color (not the blue-green species) are D. matoubensis James, 1996 and D. musciphila James, 1996 which both have fewer nephridia (8) and larger penial setae, though still quite small. All four species have longer lateral typhlosoles, and the only ones with 12 nephridia are blue-green. A fifth taxon in the acaecate group, left undescribed in James (1996), is epilobous, has 12 nephridia but also is blue-green in life.

Comparing D. spolstoni n. sp. to the other acaecate species in this paper, it has more nephridia (12 vs 10) and is not blue-green or containing elements of green pigmentation. The degree of green pigmentation could be related to habitat but we have no way of determining this.

Figures

FIGURE 1. Dichogaster spolstoni n. sp. A. Dorsal view, recently fixed. B. Ventral view. C. Ventral view clitellum region. D. Spermatheca.