Hadrobolus Cook, 1897

Enghoff, Henrik, 2011, East African giant millipedes of the tribe Pachybolini (Diplopoda, Spirobolida, Pachybolidae), Zootaxa 2753, pp. 1-41 : 30

Genus Hadrobolus Cook, 1897

Type species: Spirobolus crassicollis Peters, 1855

Included species. Hadrobolus crassicollis ( Peters, 1855)

Diagnosis. A genus of East African Pachybolini characterized by

- no coxal lobes on male legs 6 and 7

- one pair of ventral macrosetae on male legs from pair 5 onward - a distinct mesal process ca. at midlength of posterior gonopod - no striated membranous lamellae at tip of posterior gonopod - no mesal process, no free solenomerite, no distal complex of parallel ridges on posterior gonopod - no long meso-distal process on anterior gonopod coxite

- no overlapping lobes on anterior gonopod telopodites

(female characters unknown)

Cook (1899) listed a number of characters separating Hadrobolus from his “ Pachybolus ” (which also included species now classified in Pelmatojulus ). In addition to the characteristic mesal process of the posterior gonopod, these are:

- sternum of anterior gonopods very broad and short, being scarcely produced in the middle

- telopodites of anterior gonopods widely separated (“in Pachybolus they are crowded mesad by the flagella [= posterior gonopods]...”)

- the last podomere (tarsus) of male legs greatly elongated in comparison with the penultimate podomere (tibia) ( Fig. 71 )

- the ventral pad of the male tarsus oblong and extending the whole length of the podomere, the subterminal setae being farther apart

- the ventral pad “fleshy throughout, the sides being scarcely chitinized and the surface being convex or irregularly shrunken” as opposed to the condition in Pachybolus sensu Cook where “the sides of the pad are much more prominent, strongly chitinized, and dark coloured, while the surface is also of firm texture and always uniformly and strongly concave.

In the light of the variability seen between the genera recognised here, the two gonopodal characters listed by Cook (1899) are insignificant. The tarsus of Hadrobolus crassicollis ( Figs 7 , 71 ) is indeed quite long (and the tibia ventrally quite short), but not strikingly different from what is seen in the other genera ( Figs 4–6 , 60 ). The ventral pad in H. crassicollis is slightly, but not dramatically longer than that of Pelmatojulus, Gabolus , Crurifarcimen, Hyperbolus, Parabolus , Madabolus and Epibolus . The drawing of the pads in Pachybolus tectus by Cook (1899) ( Fig. 60 ) shows a much shorter pad, so maybe it is Pachybolus s.s. that differs markedly here. The ventral surface of the pad in H. crassicollis is indeed particularly soft and convex, where in the other genera this surface is concave and delimited by a sharp rim, the difference is, however, not at all obvious in the scanning electron microscope ( Figs 4–8 ). The significance of these differences cannot be properly evaluated until fresh material of Hadrobolus and Pachybolus s.s. can be studied.

Figures

FIGURES 58 – 72. Plate LII from Cook (1899), relabelled. 58 – 65. Pachybolus tectus. 58: head and first six body rings, lateral view, 59: telson: lateral view, 60: male leg, 61: gonopods, anterior view, 62: do: posterior view, 63: do: lateral view, 64: posterior gonopod, posterior-lateral view, 65: do., anterior-mesal view. 66 – 72. Hadrobolus crassicollis. 66: gonopods, anterior view, 67: do., posterior view, 68: do., lateral view, 69: posterior gonopods, anterior-lateral view, 70: do., posterior-mesal view, 71: male leg, 72: first six body rings.

FIGURES 4 – 8. Male legs, SEM. 4: Crurifarcimen vagans n. gen., n. sp., paratype, tarsus, lateral view. 5: C. vagans, paratype, tarsus, ventral view. 6: Epibolus pulchripes, tarsus, lateral view. 7: Hadrobolus crassicollis, holotype, ventral-lateral view. 8: C. vagans, paratype, surface structure of ventral pad. Scales 1 mm (5, 7), 0.1 mm (4, 6), 0.01 mm (8).