Helicochetus Attems, 1909

Enghoff, Henrik, 2018, A mountain of millipedes VI. New records, new species, a new genus and a general discussion of Odontopygidae from the Udzungwa Mts, Tanzania (Diplopoda, Spirostreptida, Odontopygidae), European Journal of Taxonomy 394, pp. 1-29 : 10-11

Genus Helicochetus Attems, 1909

Helicochetus Attems, 1909a: 158 .

Type species

Spirostreptus dimidiatus Peters, 1855 , by original designation. See further below.

Other included species

Helicochetus aberrans Kraus, 1966 ( Zambia) , H. digititarsus Kraus, 1957 ( Democratic Republic of the Congo, Tanzania), H. electricus Kraus, 1958 ( Democratic Republic of the Congo), H. gregorii ( Pocock, 1896) ( Kenya) , H. inversus Kraus, 1958 ( Democratic Republic of the Congo), H. involutus Attems, 1935 ( Democratic Republic of the Congo), H. laciniatus Attems, 1935 ( Democratic Republic of the Congo), H. levifolius Attems, 1914 (”Sambesi”, Mozambique), H. monodon Kraus, 1960 ( Zambia) , H. mutaba Kraus, 1960 ( Democratic Republic of the Congo), H. pococki (Carl, 1909) ( Tanzania) , H. rarus Kraus, 1958 ( Democratic Republic of the Congo).

Kraus (1960) provided an identification key to the species, except H. aberrans .

Remarks

The material from the Udzungwa Mts includes specimens of two species of Helichochetus. Separate descriptive notes are given for each species, but two characters shared by both species may prove to be genus-characteristic and are therefore commented on here.

LIMBUS ( Fig. 4A, C, E ). Kraus (1960) characterized the limbus of Helichochetus (translated from German): “Limbus divided by rounded indentations into processes which each carry three to six nail-like points. Limbus very broad, ca. 10 × as broad as the processes, with a silky sheen due to the characteristic surface sculpture (exception H. laciniatus )”. The limbus of the two studied species, especially H. mutaba , is indeed very broad ( Fig. 4A, C ), and the processes and nail-like points agree fully with Kraus’ description. It is not clear from his publications ( Kraus 1960, 1966) what he meant by the “characteristic surface structure”. The SEM images ( Fig. 4A, C, E ) provide no clue. There is, however, another remarkable detail, visible in Fig. 4E : under the limbus proper, there is a “sub-limbus” consisting of rounded, almost semicircular lobes.

CYTOSCUTE DENTICLES ( Fig. 4B, D, F ). The “cytoscutes”, i.e., cuticular “cells” each corresponding to a hypodermis cell ( Fusco et al. 2000) very often carry a row of tiny denticles along one edge. In both studied species of Helicochetus , these denticles are much larger than normal and point away from the cuticular surface rather than lying parallel to it.

Figures

Fig.4.Helicochetusspp.,♂♂,fromUdzungwaMts.A–B.H.dimidiatus(Peters,1855).C–F.H.mutaba Kraus, 1960. A, C, E. Limbus; in E the limbus proper is damaged (remains are seen to the left), so the round-lobed “sublimbus” becomes visible.B, D, F. Surface microsculpture of limbus. Scalebars:A, C, E = 0.01 mm; B, D, F = 0.002 mm.