Microchaetus distasmosus, Plisko, 2003

Plisko, Jadwiga Danuta, 2003, Eleven new South African earthworms (Oligochaeta: Microchaetidae) with new information on some known species, and an inventory of the microchaetids of KwaZulu-Natal, African Invertebrates 44 (2), pp. 279-325 : 282-284

Microchaetus distasmosus sp.n.

( Figs 2–3 )

Etymology: G. distasmos = uncertainty. Refers to the unusual combination of internal characters observed in this species.

Material examined: KwaZulu­Natal: Holotype NMSA /Olig.02532 Mapelane Nature Reserve (28º54'S: 31º55'E) at the edge of forest and grassland, from moist, sandy soil, 26 November 1996, JDP, TL. Paratypes: NMSA /Olig.02377, 6 not fully mature, with tubercula pubertatis, collected together with holotype; NMSA /Olig.00626a Umfolozi Game Reserve (28º22'S: 31º52'E) on high bank of White Mfolozi River , grassland, sandy moist soil, 24 February 1990, 20 cl + 10 juv, JDP [associated with natalensis ] .

Description based on holotype and paratypes.

External characters:

General: body cylindrical, extended during preservation. Colour: holotype and paratypes preserved in alcohol for over six years do not reveal pigmentation; grey. Dimensions: holotype preserved, much extended, 75 mm long, 2 mm wide at 10, 2. 5 mm wide at tubercula pubertatis; paratypes 55–80 mm long, 2 mm wide at 10, 3–4 mm at tubercula pubertatis. Segment number: holotype 197+ (complete number is uncertain, due to poor preservation); paratype 163. Prostomium: prolobous, small. Segmentation: secondary annulation present on preclitellar segments; 1 and 2 short, simple, with obvious intersegmental furrow 1/2, both segments with irregular longitudinal grooves; 3 simple; 4–8 with two ringlets, first longer than second; 9 with two ringlets, second short; 10 and the following simple, postclitellarly randomly demarcated. Setae: minute, closely paired. Nephridial pores: not observed. Female pores: obvious on paratypes, paired in 14 below c setae. Male pores: externally not observed; possibly in intersegmental furrow 18/19, as vasa deferentia enter body wall in 18. Spermathecal pores: externally not observed.

Clitellar region ( Figs 2–3 ): Clitellum: saddle­shaped, white, elongated, clearly segmented, on 1/n11,12–28,29; anterior and posterior borders not clearly marked; anteriorly ventral borders extend to line of papillae located on ab setae; on 18–27 bordering tubercula pubertatis. Tubercula pubertatis: on holotype and paratypes well developed glandular tubercles, segmented, on 18,19–27,28; ventrally extending to ab setae. Papillae: different sizes and shapes, glandular, encircling ab setae on first ringlets of 5–7 and also on 11–18 ( Fig. 3 ).

Internal characters:

Septa: 4/5 thin, 5/6 and 6/7 most thickened; 7/8 and 8/9 little thickened. Gizzard: cylindrical, large, muscular, in 7. Calciferous glands: in 10 large, separated dorsally and ventrally. Intestine: commences in 13. Typhlosole: in holotype commences in 20 as thin tube, slightly enlarging backwards, terminating in segment 75. Dorsal blood vessel: 4–8 double, separated; 9 double, close, cordiform. Paired dorsoventral vessels: 4–8 enlarged vessels; 9–11 moniliform. Nephridia: meganephridia ; little coiled loops with thin, extended caeca. Spermiductal funnels: holandric arrangement; two pairs, each closely connected posteriorly with anterior parts of seminal vesicles, in 10 and 11 respectively. Vasa deferentia : difficult to observe due to softened body wall and decomposed tissues; probably enter body wall at posterior part of segment 18. Seminal vesicles: two pairs of large sacs commencing at septa 10/11 and 11/12 respectively. Spermathecae: small, elongated thecae in 8 and 9; 1–2 at each side, close to intersegmental furrow 8/9 and 9/10 respectively; ectal parts probably in 8/9 and 9/10, although anterior not confirmed. Ovaries: not observed. Genital glands: glandular tissues in 15, and 18–27 associated with internal glands of tubercula pubertatis.

Biological notes: Mapelane Nature Reserve comprises coastal dune forests extending southwards from the Mfolozi riverbank with a variety of woodland patches and grasslands. Holotype and some paratypes were found at the edge of large patches of grassland, about 10 km south from the river mouth. The other paratypes were collected north­west of the holotype site on the bank of the White Mfolozi River, covered by high indigenous grasses, and were associated with natalensis . Both localities are similar in vegetation and soil. Transportation of cocoons or individuals by water or in mud can be expected.

Distribution: Known only from the Mfolozi River banks ( Fig. 1 ).

Discussion: A distinctive species although similar and probably related to quaerus described below. Both species have spermathecae in segments 8 and 9. The location of spermiductal pores in intersegmental furrow 8/9, however, was not confirmed in distasmosus . M. distasmosus also differs from quaerus in the length and position of the clitellum, shape of tubercula pubertatis, and thickness of preclitellar septa. In the other species of Microchaetus the most anterior position of spermathecal pores was observed in namaensis (known only from the Northern Cape) which has the anterior pores in 9/10 and the posterior in intersegmental furrows 10/11 11/12 respectively. In the other two holandric genera Tritogenia and Michalakus , the most anterior positions of spermathecal pores are in intersegmental furrows 10/11 11/ 12 in Tritogenia shawi and T. soleata , and in 10/11 11/12 12/ 13 in Michalakus initus .

It is noteworthy that in some members of the genus Proandricus assigned to the lesothoensis ­ species group, the utmost anterior spermathecal pores occur in 9/10, or between ringlets in segment 9 ( Proandricus amphius sp. n. and P. oresbiosus sp. n.).

Figures

Figs 2–3. Microchaetus distasmosus sp. n. 2. Holotype, anterior part of body, ventral view with clitellum and tubercula pubertatis. 3. Paratype, clitellar region, enlarged. [C = clitellum, T = tuberculum pubertatis].

Fig. 1. The distribution of species of Microchaetus and Michalakus in KZN. Microchaetus: 1 = ambitus; 2 = caementerii; 3 = distasmosus; 4 = griphus; 5 = herberti; 6 = idechoritus; 7 = mkuzi; 8 = natalensis; 9 = papillatus; 10 = parvus; 11 = pondoanus; 12 = quaerus; 13 = tuberosus; 14 = vernoni; 15 = zaloumisi; 16 = Michalakus initus.