New and little‐known earthworm species from the Ivory Coast (Oligochaeta: Acanthodrilidae: Benhamiinae and Eudrilidae)

In the framework of the international project called “Conservation and Sustainable Management of Below‐Ground Biodiversity”, soil macrofauna collections were carried out in the Centre‐West Ivory Coast. Altogether, 13 earthworm species were recorded, of which four belonged to the family Eudrilidae and nine to the family Acanthodrilidae. From the species collected, two, Dichogaster (Dichogaster) eburnea sp. nov. and Dichogaster (Dichogaster) mamillata sp. nov., proved to be new to science. To accommodate the enigmatic eudrilid earthworm species Scolecillus compositus Omodeo, 1958, a new genus, Lavellea gen. nov., is proposed.


Introduction
The earthworm fauna of Ivory Coast is one of the most well known in Africa. Since the beginning of the 1950s, several taxonomic and many more ecological papers have been devoted to the earthworm research carried out in this West African country (e.g. Sciacchitano 1952;Omodeo 1955aOmodeo , 1955bOmodeo and Vaillaud 1967; total earthworm diversity of the region investigated. Therefore, it is not surprising that a survey of a previously unexplored territory reveals several undescribed species.
Most of the samples presented here were collected in the framework of the international project ''Conservation and Sustainable Management of Below-Ground Biodiversity'' in the Centre-West Ivory Coast. This project is being undertaken simultaneously in seven countries and aims, in the first phase, to assess the impact of land management on soil organisms across a gradient of forest disturbance.

Study site
Earthworms were collected in the Oumé region (6u379N, 4u409W), located in the Centre-West Ivory Coast and characterized by semi-deciduous degraded forests (Chatelain et al. 2003). Altitude ranges from 100 to 180 m and rainfall  ranges from 849 to 1764 mm. The annual rainfall in 2004 peaked at 1540.9 mm while monthly average temperature is about 26uC. Morphological characterizations revealed that the soils of the area are ferrasols (FAO-UNESCO 1989) of homogeneous distribution across the landscape, but with differences related to topography (Angui, unpublished data). The surface organic layer is thin (20-30 cm), friable (resistance to penetration varies between 200 and 1000 kPa), and well mineralized.

Earthworm sampling protocol
Earthworms were sampled based on the tropical soil biology and fertility methods (Anderson and Ingram 1993). At each sampling point, a soil monolith of 25 cm 2 and 30 cm depth was extracted after digging a trench 30 cm deep all round. The monolith was sampled at three depths (0-10, 10-20, and 20-30 cm); earthworms were hand sorted and preserved in 4% formaldehyde for taxonomic identification. Altogether, 107 soil monoliths were sampled across the study site.

Penial setae handling
The penial setae were removed by dorsal dissecting of the specimens and mounted in Euparal for light microscopic study. Microscopic photos were taken using a Nikon Coolpix 990 digital camera attached to a Nikon E660 DIC microscope. All the material is deposited in the Oligochaeta collection of the Hungarian Natural History Museum (HNHM). The following abbreviations are used in the text: L., length; D., diameter; No. segments, number of segments.

Remarks
In the original description (Sciacchitano 1952) the female pores are mentioned as paired openings, but on the drawings of Omodeo (1955a, p 226, Figure 6a) depiction is as a single ventral-median organ. In our material the female pore is also single and this casts doubt on the correctness of the original description on this point.

Derivatio nominis
The specific epithet is from the Latin eburneus5ivory, referring to the country.

Internal characters
The first septum 6/7, thickened septa lacking. Oesophageal gizzards two, in segments 5 and 6. Three pairs of calciferous glands located in segments 15-17, their size increasing backwards. Excretory system meroic, with three meronephridia on each side. Paired hearts are present in segments 10-13. Typhlosole strong, begins in segment 20. Testes are free in 10 and 11. Seminal vesicles small in 11, 12, and ovary in segment 13. Seminal duct convoluted, discharging in segment 18. Two pairs of small prostatic glands are present in 17 and 19, confined into their own segment and each provided with a penial setal sack containing two different types of penial setae. The larger one is about 0.35 mm long and 0.005 mm wide with a sharply pointed tip ( Figure 2C). Ornamentation consists of strong scattered teeth. The smaller one is almost smooth, about 0.3 mm long and 0.005 mm wide with rounded tip ( Figure 2D). There are two pairs of T-shaped spermathecae in segment 8 and 9. The ampoule is folded back and bears a small finger-like pseudodiverticulum. The duct is small and joins to the ampoule at right-angles ( Figure 2B).

Remarks
This species belongs to the cyrtochaeta species group and resembles D.

Derivatio nominis
The specific epithet from the Latin mamillae5nipples, refers to the special protuberances of the prostatic pores.

Internal characters
The first septum 4/5, thickened septa lacking. Oesophageal gizzards two, in segments 5 and 6. Three pairs of calciferous glands located in segments 15-17, their size slightly increasing backwards. Excretory system meroic, with four meronephridia on each side. Paired hearts are present in segments 10-13. Typhlosole strong, begins in segment 21. Testes are free in 10 and 11. Seminal vesicles small in 11, 12, and ovary in segment 13. Seminal duct apparent highly convoluted, discharging in segment 17. A pair of small prostatic glands are present in 17, confined to their own segment, each with a penial setal sack containing one mature and one juvenile seta. The mature seta is about 1 mm long and 0.005 mm wide with spatula-like tip. The ectal third is undulated and ornamented with scattered teeth ( Figure 4C). One pair of spermathecae in segment 9. The ampoule is elongated sac-like and as long as the muscular duct. In the wall of the duct there are several somewhat protruding seminal chambers ( Figure 4B).

Remarks
Due to the presence of triannulate segments and pad-like genital papillae, D. (D.) terraenigrae greatly resembles the species of the genus Millsonia externally, but the presence of penial setae and the lack of intestinal caeca obviously place it in Dichogaster. However, the reduction of the calciferous glands in segment 16 requires further consideration regarding its taxonomic status. Subfamily PAREUDRILINAE Beddard, 1894 Lavellea gen. nov. Omodeo 1958, p 89 (part). Chuniodrilus: Wasawo and Omodeo 1963, p 217 (part). Stuhlmannia: Sims 1987, p 380 (part).

Derivatio nominis
The new genus is named in honour of the renowned earthworm ecologist and pioneer of the Ivorian earthworm study Dr Patrick Lavelle, Paris.

Remarks
Scolecillus compositus was described by  as a second species besides the generotype Scolecillus tantillus . However, S. compositus differs from S. tantillus in several characters of great taxonomic importance such as the presence of penial setae and the paired nature of the oviductal system. This led Wasawo and Omodeo (1963) to place this species together with the newly described C. vuattouxi in the genus Chuniodrilus Michaelsen, 1913. But these species differ again from the Liberian generotype C. schomburgki Michaelsen, 1913 by lacking an oesophageal gizzard, therefore Sims (1987) transferred compositus to Libyodrilus and vuattouxi to Stuhlmannia (but in this case with a question mark).
Recently, Clausen (2004) reviewed the genus Libyodrilus and proved that S. compositus differs substantially from the members of this genus. Therefore she rejected this placement without suggesting a proper place for this species. As S. compositus and C. vuattouxi (both from the Ivory Coast) do not fit any existing Pareudrilinae genus, Lavellea gen. nov. is proposed to accommodate them.
The new genus differs from Scolecillus in having penial setae and from Chuniodrilus in the lack of oesophageal gizzards.