Helicochetus dimidiatus ( Peters, 1855 )

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 : 11-14

Helicochetus dimidiatus ( Peters, 1855)

Figs 4A–B , 5

Spirostreptus dimidiatus Peters, 1855: 79 .

Helicochetus dimidiatus – Attems (1909a): 158.

Material studied (total: 1 ♂)

TANZANIA: 1♂, Morogoro Region, Udzungwa Ecological Monitoring Centre, Mang’ula , 07°50′44.9′′ S, 36°53′28.2′′ E, 339 m a.s.l., 20 Mar. 2013, T. Pape and N. Scharff leg. ( ZMUC).

Description

Male

Based on studied specimen. Details from previous descriptions in parentheses.

SIZE. Diameter 5.4 mm, 59 podous rings, no apodous rings in front of telson. ( Peters 1855: length 65– 60 mm; diameter 5–5.5 mm; 62 “annuli”; Peters 1862: length 60–70 mm; diameter 5 mm; 66 body rings; Verhoeff 1901, ♂, as Odontopyge attemsi Verhoeff, 1901: length 62½ mm; 61 body segments.)

COLOUR. After 4 years in alcohol greyish; head, antennae, legs, and posterior ca 40% of metazonites yellowish.

HEAD. Without peculiarities. Supralabral setae not countable due to damage. ( Peters 1855, 1862: 6–7; Verhoeff 1901: 5; Attems 1914: 6.)

COLLUM. With two complete furrows on each side, none of them marginal. ( Peters 1855: a marginal and two further striae; Verhoeff 1901: four striae; Attems 1914: a marginal ridge, then an incomplete, and then two complete striae.)

BODY RINGS. Almost perfect cylinders, not vaulted; suture straight; ozopores starting from ring 6, placed ca ⅓ of metazonite length between suture and limbus. Ca 13 metazonital striae reaching almost up to ozopore. Surface microsculpture ( Fig. 4B ), see Remarks for genus.

ANAL VALVES. Each with a moderate dorsal spine; margins raised; each valve with three marginal setae not borne on tubercles.

LIMBUS ( Fig. 4A ). See Remarks for genus.

MALE LEGS. With postfemoral ventral pads from first post-gonopodal leg-pair 3–5 until ca midbody; anteriormost and posteriormost pads small, intermediate ones covering entire ventral side of postfemur.

GONOPOD COXA ( Fig. 5A–D ). As typical for the genus, including small, distal basad process (bp) ( Fig. 5B, D ). Prostatic stylet (sp) visible in coxal cavity ( Fig. 5B–C ).

GONOPOD TELOPODITE ( Fig. 5E–H ). Tip of solenomere (slm) tightly spiraled (like a corkscrew) ( Fig. 5H ); no processes visible in spiral. Telomere (tm) ending in long, slender process with a terminal brush of long fringes ( Fig. 5F–G ).

Female

Unknown.

Distribution and habitat

Known from several localities in Mozambique and Tanzania ( Enghoff et al. 2016).

Verhoeff (1901) quoted a report on H. dimidiatus (as Odontopye attemsi Verhoeff, 1901) from the small island of Kwale (off the southern Tanzanian coast) where this species appeared in very large numbers, destroyed the islander’s crops and forced them to move their agricultural activities to the mainland.

Helicochetus dimidiatus is sometimes kept in terraria, see, e.g., www. diplopoda .de/html/species/ hdimidiatus/_helico.php (accessed 19 Apr. 2007).

Remarks

The prostatic stylet (“stylet prostatique” sensu Brolemann 1920) is rarely seen, but seems to be a general feature of odontopygid and spirostreptid gonopods ( Brölemann 1917; Brolemann 1920; Kraus 1966). This structure has been regarded as homologous with the cannula of Polydesmida and the flagella of many Julida, Cambalidea and Chordeumatida , in which case it would constitute a synapomorphy of subterclass Eugnatha sensu Enghoff et al. (2015); see discussions by Brolemann (1932), Demange (1967) and Enghoff (1984).

Figures

Fig. 5. Helicochetus dimidiatus (Peters, 1855), ♂, from Udzungwa Mts. Left gonopod. A–D. Coxa. A. Mesal view. B. Anterior view. C. Prostatic stylet. D. Apical basad process. E–H. Telopodite. E.Anterior view (the area markedwith blue iscovered by the mounting tape). F. Posterior view.G. Tip of telomere. H. Tip of solenomere.Abbreviations: bp = apical basad process of coxa; mp = metaplica; pp = proplica; slm = solenomere; sp = prostatic stylet; tm = telomere. Scale bars:A–B, E–F = 0.2 mm; C–D, H =0.02 mm; G = 0.05 mm.

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.