Microchaetus herberti, Plisko, 2002

Plisko, Jadwiga Danuta, 2002, Three new earthworm species of Microchaetus Rapp, 1849, and new data on two earlier known species of this genus (Oligochaeta: Microchaetidae), African Invertebrates 43, pp. 205-214 : 208-210

Microchaetus herberti sp. n.

( Fig. 2 )

Etymology: Named for Dr D. G. Herbert of the Natal Museum’s Department of Malacology, who collected and donated the type material to the Oligochaeta Department. Material examined: SOUTH AFRICA: KwaZulu-Natal: Holotype NMSA/Olig.03484, clitellate, Port Shepstone area, Marble Delta (30º39.056'S: 30º21.361'E) under accumulated layer of litter in dense valley thicket/woodland, heavily invaded by Lantana and Chromoleana, 5 October 2001. Paratypes: NMSA/Olig.03485, 1 with absorbed clitellum and 1 juvenile, collected together with holotype; NMSA/Olig.03483, 1 clitellate, under stone in Oribi Gorge Nature Reserve (30º43.5'S: 30º16.5'E) in scarp forest on SE side of Umzimkulwana River, 5 October 2001. Other material: Port Shepstone area: NMSA/Olig.03536, Marble Delta, north side of Umzimkulwana River at base of Simuma Hill (30º40.367'S: 30º20.563'E) in dense riverine thicket/woodland, heavily invaded with Lantana and Chromoleana, in deep leaf-litter/soil, 4 December 2001, 4 clitellate and 5 juvenile; NMSA/Olig.03538, Marble Delta, in badly degraded bush clumps in quarry site (30º39.08'S: 30º21.5'E), under large log, 5 December 2001, 4 clitellate; NMSA/Olig.03539, Natal Portland Cement Nature Reserve (30º40.456'S: 30º20.299'E) in dense riverine woodland, not on limestone, under stones and in leaf-litter, 4 December 2001, 3 clitellate and 1 juvenile.All material collected by D. G. Herbert.

Description based on holotype and paratypes.

External characters:

General: Body cylindrical. Colour: In life dorsally violet, ventrally yellowish-grey; alcohol-preserved dark grey dorsally on whole length of body, ventrally light grey. Dimensions: Holotype preserved and slightly contracted 367 mm long, 10 mm wide at segment 10, 18 mm wide at tubercula pubertatis; paratype 334 mm long, 12 mm wide at segment 10, 18 mm at tubercula pubertatis. Segment number: Holotype 278. Prostomium: Prolobous, large, with deep longitudinal grooves. Segmentation: Secondary annulation present on preclitellar segments: segments 1 and 2 short, both with longitudinal grooves; 3 simple; 4–8 with simple, irregularly annulated ringlets, similar in size and appearance; 9 with two ringlets, second shorter than first; 10 and following segments simple, postclitellar randomly annulated. Setae: Moderate in size, closely paired; first pairs on segment 3; on 4–9 on first ringlet; on segment 10 ab = cd, aa <bc; on segments 15–24 ab setae much enlarged, associated with papillae and genital glands. Nephridial pores: Conspicuous in cd setal lines; first pair in intersegmental furrow 3/4. Female pores: Not observed, probably embedded in wall tissue of segment 14. Male pores: In intersegmental furrow 15/16, marked by small depressions, laterally to rimmed anterior parts of genital fields. Spermathecal pores: In intersegmental furrows 13/14 and 14/15, minute, difficult to trace.

Clitellar region ( Fig. 2 ): Clitellum: On holotype and one mature paratype well developed, saddle-shaped, over segments 13–24, dorsally extending into a small portion of 25; anteriorly clearly bordered, parallel with intersegmental furrows; lateral edges on 13–14 along with cd setae, on 1/n15–1/n19 slightly below dorsal edges of tubercula pubertatis; on 1/n19–24 parallel with rims of genital fields. Tubercula pubertatis: Glandular ridges with deep irregular grooves, on 1/n15–1/n19; nearly rectangular with rounded corners, rimmed; on segments 16 and 18 at their dorsal corners bordering with clitellum a pair of triangular cushions overlapping clitellum edge. Genital fields: Two separated, elongated glandular cushions, rimmed laterally, extending backward over segments 15–24; the median distances between both cushions on 15–18 are nearly equal to width of glandular cushion; on the following segments distances increase and become at 24 nearly twice that on 15. Papillae: On segments 13–24 associated with large genital setae .

Internal characters:

Septa: 4/5 thickened, strong, elastic; 5/6 thin, 7/8 8/9 very much thickened, muscular, massive; following septa thin but firm. Gizzard: Globular, in segment 7; posteriorly softened. Calciferous glands: In segment 9, small, muscular, hemispherical glands, laterally adherent to oesophagus, clearly separated dorsally and ventrally. Intestine: Commences in 13. Typhlosole: Commences abruptly as very thick, folding tube in segment 22; in holotype terminates in segment 198. Dorsal blood vessel: Double in 5– 9; in 5–7 thin tubes, close one to another; in 8 widely separated; in 9 two enlarged vessels forming cordiform organ. Paired dorsoventral vessels: Present in segments 5– 11; 5–8 thin vessels, in 9–11 very much enlarged, moniliform ‘hearts’. Nephridia: Meganephridia ; large coiled loops and elongated V-shaped caeca, one pair per segment.

Reproductive organs: Spermiductal funnels: Holandric arrangement (two pairs); in 10 and 11; large, iridescent, enclosed in separated sacs. Vasa deferentia: Commence in segments 10 and 11 respectively on lateral sides of spermiductal funnels, and extend transversely before curving posteriorly to run backward separately, parallel to axis of body, to posterior part of segment 15, where they enter body wall and consequently male pores. Seminal vesicles: Two pairs sacs commencing at posterior parts of septa 10/11 and 11/12 respectively; large pouches closely confined to spermiductal funnels of segments 10 and 11 extend into segments 11 and 12 respectively. Spermathecae: Irregularly shaped, small thecae deeply embedded in body wall of segments 13 and 14, with their pores at intersegmental furrows 13/14 and 14/15. Number of spermathecae varies; in holotype in segment 13 at its left side were 11 spermathecae, in segment 14 were 17 thecae; in dissected paratype were 7 thecae in segment 13, and 17 thecae in segment 14. In the other paratype no spermathecae were found at right side of segment 13, being probably deeply embedded in body wall. Ovaries: Not detected. Genital glands: Not observed. Genital setae: In segments 15–24; in each segment two large setae in one oblong tube; associated with papillae and genital fields.

Distribution: Known from the southern KwaZulu-Natal coastal hinterland area. Found in protected area of Oribi Gorge Nature Reserve, and along the lower Umzimkulwana River; possibly also occurring along the Umzimkulu River.

Biological notes: Collected at the confluence of the Umzimkulu and Umzimkulwana Rivers , known as Marble Delta.The area constitutes one of the few limestone deposits in KwaZulu-Natal. Currently it is heavily exploited as a mineral resource and there is massive habitat degradation. Rehabilitation of the quarried area is minimal, and the area is heavily infested with alien plants. The vegetation ranges from patches of grassland on the exposed ridges, to valley thicket and denser thicket/woodland in the south-facing gullies and valleys. The holotype was found in dense valley thicket/woodland under accumulated litter. Other specimens were found near the holotype locality, on the bank of the Umzimkulwana River in scarp forest in the Oribi Gorge Nature Reserve , where no limestone occurs. Finding of paratypes in the much higher area of the Oribi Gorge Nature Reserve suggests the possibility of species transportation in the water of the Umzimkulwana River running through the Reserve up to the area of Marble Delta. Species occurrence in a much-degraded habitat, in an area with soil rich with calcium, suggests an ability to adapt to degraded conditions. However, it is worth noting that in the paratype gathered together with the mature holotype, the clitellar area is marked by brownish colour, and both seminal vesicles are slightly reduced. This could suggest species regression, followed by aestivation, quiescence or facultative phases caused by dryness in this area in June–September, or indicate unfavourable environmental conditions .

Two fully developed specimens collected in October suggest sexual reproduction at the beginning of the rainy season, which starts at the end of September. The species is associated with M. zaloumisi Plisko, 1992 .

Discussion: Similar to M. natalensis ( Kinberg, 1867) . In both species the spermathecal pores occur in intersegmental furrows 13/14 and 14/15, and the calciferous glands are in segment 9. However, herberti is much larger than natalensis , and its tubercula pubertatis and genital fields differ in shape conspicuously.

Figures

Fig. 2. Microchaetus herberti sp. n. Ventral view of anterior part of body with clitellar region and tubercula pubertatis.