Diaphorodesmus dorsicornis (Porat, 1894)

VandenSpiegel, Didier, Golovatch, Sergei I. & Mauries, Jean-Paul, 2016, Review of the western African millipede genus Diaphorodesmus Silvestri, 1896 (Diplopoda, Polydesmida, Chelodesmidae), with the description of a similar, but new monotypic genus from Cameroon, ZooKeys 600, pp. 7-24 : 9-11

Taxon classification Animalia Polydesmida Chelodesmidae

Diaphorodesmus dorsicornis (Porat, 1894) Figs 1, 2, 3, 4, 5, 6, 7, 12

Paradesmus dorsicornis Porat, 1894: 33, figs 3-3c (D).

Diaphorodesmus dorsicornis - Silvestri 1896: 197 (D) (erection and typification of Diaphorodesmus ); Cook 1896: 16 (D); Attems 1899: 312, plate 7, fig. 167 (D) (reiterated original description and a reproduced original figure); 1931: 100, figs 147-151 (D, R); 1938: 409, figs 451-452 (D, R); Carl 1905: 271, plate 6, fig. 1-1a (D, R).

Diaphorodesmus attemsii Verhoeff, 1938: 167, figs 1-3 (D), syn. n.

Diaphorodesmus attemsii - Attems 1940: 560 (D, R).

Campodesmoides corniger VandenSpiegel, Golovatch & Nzoko Fiemapong, 2015: 2, figs 1-3 (D), syn. n.

Material examined.

Apart from the type series of Campodesmoides corniger , deposited at MRAC ( VandenSpiegel et al. 2015), the following unpublished samples are available.

1 ♂ (MNHN JB254), Cameroon, Kumba, 25.XI.1975, leg. M. Lamotte ( Diaphorodesmus dorsicornis , det. J.-P. Mauriès); 5 ♂, 2 ♀ (ZMUC), eastern Nigeria, Osomba 56 miles from Calabar, 17.VI.1965; 1 ♀ (ZMUC), eastern Nigeria, 1963, all leg. V. Schiøtz ( Diaphorodesmus attemsii , all det. H. Enghoff).

Revised published material.

1 ♂, 2 juveniles (fragments of caudal body part only) (ZSM Reg. No. A 20052425 + slide A 20035316), “Kamerun”, without further information ( Diaphorodesmus dorsicornis , det. K.W. Verhoeff).

Remarks.

This species enjoys several descriptions, the latest of which ( VandenSpiegel et al. 2015) is particularly complete and detailed. We only add here more pictures and drawings (Figs 1-7) to show evident variations in some somatic and gonopodal characters that bridge Diaphorodesmus dorsicornis and Diaphorodesmus attemsii and justify their synonymization.

Considering the measured material published elsewhere ( Porat 1894; Attems 1938; VandenSpiegel et al. 2015) and here, body size variations are quite considerable both between individuals and, to a lesser degree, sexes: length 26-35 mm (♂, ♀), width of midbody pro- and metazonae 2.1-3.5 and 3.0-4.9 mm (♂) or 2.5-3.6 and 3.6-5.0 mm (♀), respectively. General coloration varies from yellow through grey-brown to blackish ( Porat 1894; Carl 1905; Attems 1931, 1938; VandenSpiegel et al. 2015).

As regards the somatic characters mentioned by Verhoeff (1938) and quoted above that distinguish Diaphorodesmus attemsii from Diaphorodesmus dorsicornis , they are actually mistaken or reflecting individual variations. Thus, the dorsal horns on metaterga 4 are typically somewhat shorter in the ♀ compared to the ♂, and they tend to be more or less gradually and increasingly reduced from metatergum 2 to 4 in both sexes. The higher the horns on metatergum 4, the less strong their shift forward off the caudal margin. This shift is usually particularly apparent in the ♀.

The more or less evident cones in front of these horns are usually subequal in shape and size, 2+2, arranged in a transverse row (Fig. 1A, C, D). However, occasionally there are variations observed in shape and size of those cones as well. The pertinent material of Verhoeff (1938), at least the single adult ♂ at his disposal which is currently kept at the ZSM, shows the typical 2+2 (not 3+3!) cones, albeit the central pair is indeed a little larger than the lateral one, while the dorsal horns are relatively short, tuberculiform, clearly set off from the caudal margin of the metatergum (Fig, 1E, F). The gonopod structure of the ZSM ♂ is likewise closer to the one as depicted by Attems (1931) for " Diaphorodesmus attemsii " (Fig. 4).

The single relatively large sample in our hands, that from Osomba, shows the following variations in structure of metatergum 4. Most of the samples have rather long dorsal horns which often are even slightly curved caudad and set close to the caudal margin, with 2+2 subequal tubercles/cones in front. However, in one ♂ the situation is largely the same as described above for the ZSM ♂. It shows the gonopods typical of " Diaphorodesmus attemsii " as clearly depicted by Attems (1931, 1938) (Fig. 5) and used for SEM here (Fig. 7), both horns are shorter, rather tuberculiform and clearly shifted forward off the caudal margin of the metatergum (the left horn also being nearly bifid), while the 1+1 central paramedian cones in front are a little higher than the lateral ones (Fig. 1A). All this is definitely evidence of the variability being purely individual.

The NHMW series of " Diaphorodesmus attemsii " syntypes, which contains 1 ♂ and 1 ♀ from Bibundi, 2 ♀♀ from Victoria, and a microscopic slide with the gonopods of a ♂ from Mukonje Farm, shows the same somatic variations as noted above (N. Akkari, in litt.). Thus, metatergum 4 of the ♂ from Bibundi (Fig. 1B) has typical horns, both rather high, slightly curved caudad and placed quite close to the posterior margin, whereas the cones in front are 2+2, the paramedian pair being slightly larger than the lateral one.

Hoffman, in his unpublished archives, provided the following distinctions between Diaphorodesmus dorsicornis from Diaphorodesmus attemsii , based solely on gonopod structure. The gonopod of " Diaphorodesmus attemsii " was drawn from a ♂ taken at Victoria, southwestern Cameroon (apparently, the Hamburg Museum collection, see Weidner 1960).

Hoffman used Verhoeff’s (1938) account of somatic differences (which actually do not hold, as the ZSM ♂ has the typical 2+2 cones in front of the dorsal horns!) to distinguish both Diaphorodesmus dorsicornis and Diaphorodesmus attemsii from what Hoffman evidently intended to describe as a new species. He also made several drawings of somatic and gonopodal characters, using a ♂ from Port Harcourt, southeastern Nigeria (Fig. 2). Its metatergum 4 may indeed show 3+3 cones in front of the horns (Fig. 2A), while its gonopod traits (Fig. 2 D–F) match very closely those presented by Verhoeff (1938) for the ZSM ♂ (Fig. 4).

Comparing the gonopods of Diaphorodesmus samples from a number of often disparate localities across western Africa (see Porat 1894; Carl 1905; Attems 1931; Verhoeff 1938; VandenSpiegel et al. 2015, as well as our Figs 2 D–F, 3-7), the variations observed in the relative sizes and shapes of pfp, slo, lo and sph, just like those of the above somatic features, seem to be random and too minor to consider more than individual. Therefore, we do not hesitate to formally synonymize Diaphorodesmus attemsii Verhoeff, 1938 with Diaphorodesmus dorsicornis (Porat, 1894), syn. n., treating the genus monospecific, albeit quite polymorphic. This conclusion is in accord with the vast distribution of Diaphorodesmus dorsicornis in southeastern Nigeria, southwestern Cameroon and Equatorial Guinea, western Africa (Fig. 12).