Megascolecidae Rosa, 1891

Plisko, Jadwiga D. & Nxele, Thembeka C., 2015, An annotated key separating foreign earthworm species from the indigenous South African taxa (Oligochaeta: Acanthodrilidae, Eudrilidae, Glossoscolecidae, Lumbricidae, Megascolecidae, Microchaetidae, Ocnerodrilidae and Tritogeniidae), African Invertebrates 56 (3), pp. 663-663 : 695-696

Family Megascolecidae Rosa, 1891

Megascolecidae is a second family belonging to the superfamily Megascolecoidea (compare notes for Acanthodrilidae ), and is the largest group of megadrile, accounting for around 2000 taxa recorded into various ranks and various generic/family statuses (Csuzdi 2012; Sims & Easton 1972; Easton 1979, 1982; Blakemore 2002). From these, nearly 30 species are known to be distributed worldwide and to adapt easily under various conditions in new biotopes. These species have been described/re-described under numerous synonyms in various genera, creating a long list of names. Sims and Easton (1972), Easton (1982) and Blakemore (2004 a, 2010) have eliminated a number of the synonyms and have grouped some of the accepted names into species-complexes. Species known from RSA have also been reported under various synonyms. Some of them have been positively accredited to valid species and their recorded presence in the country has been summarised by Plisko (2010). However, a large portion of the material collected in this country and accessioned in the NMSA has also been recorded under various synonyms, or simply marked as ‘ Pheretima -group’, possibly referring to a presently unidentified species. This paper includes only those species which have been positively identified and assigned to a ‘species group’, as indicated by Sims and Easton (1972) or Blakemore (2004 a), and have been found in RSA. In the case of specimens that differ from those placed in the key, it is necessary to consult other literature (Michaelsen 1900; Stephenson 1930; Gates 1972; Blakemore 2002, 2010) and newly described megascolecid species.

In RSA 12 species of three genera are known: Amynthas ( Kinberg, 1867) – eight species; Metaphire Sims & Easton, 1972 – two species; Perionyx Perrier, 1872 – one species. Pontodrilus litoralis ( Grube, 1855) , assigned to Megascolecidae by Plisko (2010), is placed separately in the Appendix of this paper. The megascolecids recorded in this key were introduced to RSA at different times, either naturally, or intentionally or coincidentally by humans, by means of one of the various mechanisms of species introduction hypothesised by Ljungstöm (1972). Their appearance in RSA has been summarised by Plisko (2010).

The species are terrestrial, occurring in cultivated fields (mostly in sugar cane plantations); in parks and gardens; in natural biotopes to which they were transported along with introduced bushes and other plants; in experimental plots; on riverbanks; and in other moist areas. They are often found in polluted spots, and are common in composting heaps, vermiculture farms, nurseries and pot plants.

All the species reproduce bisexually, although parthenogenetic reproduction is frequently noted. In parthenogenetic morphs the prostates and spermathecae may be degraded or aborted, and the male pores malformed or absent. Ljungström (1972) found that in a majority of A. diffringens the prostates and spermathecae were degraded or aborted. In the material collected from a polluted field in the Pietermaritzburg area ( KZN) it was also found that the prostates were greatly deformed, although the spermathecae were present and well developed (personal observation).

A practical/shortened characterisation of the megascolecids occurring in RSA soils may be given as follows: Body cylindrical, segments clear, not marked externally by furrows. Length 20–150 mm. May be pigmented or not. Setae perichaetine (numerous setae distributed around the body at each segment). Prostomium epilobous ( Fig 7C ). Dorsal pores present (there are external intersegmental openings to the coelomic cavity in some of the intersegmental furrows). Female pore single, in 14 (a single pore is characteristic for South African megascolecids). Male reproductive organs megascolecine (the term megascolecine indicates that the single pair of prostates open their pores in segment 18, together with the ectal part of the male ducts, in male pores). Male pores paired, in 18, postclitellar, (parthenogenetic morphs may lack male pores or these may be degenerated). Spermathecal pores paired, in some of the intersegmental furrows 4/5–8/9; the number of pores and their location are specific characters. Clitellum annular ( Fig. 5A ). Gizzard in 8–10. Intestinal caeca can be present. Ovaria paired in 13. Holandric (testes restricted to segment 10 and 11). Excretory system meroic (minute, numerous nephridial tubules in each egment) or holoic (a single pair of large nephridium in each segment). Prostate racemose (with no central canal) ( Fig. 6A ). Spermathecae paired, in pre-testicular segments. Copulatory pouches (invagination of the male pores) present or absent. Calciferous glands absent.

Figures

Fig. 7. Prostomium: (A) zygolobous; (B) prolobous; (C) epilobous; (D) tanylobous.

Fig. 5. Clitellum: (A) annular (schematic); (B) saddle-shaped (schematic).

Fig. 6. Prostates: (A) (schematic) racemose=lobular (Amynthas sp.) Megascolecidae; (B) tubular (Udeina adriani) Acanthodrilinae.