Agrophogonus pusillokiellandi Olsen & Enghoff, 2020

Olsen, Sissel Anna, Rosenmejer, Trine & Enghoff, Henrik, 2020, A mountain of millipedes IX: Species of the family Gomphodesmidae from the Udzungwa Mountains, Tanzania (Diplopoda, Polydesmida), European Journal of Taxonomy 675, pp. 1-35 : 29-31

Agrophogonus pusillokiellandi Olsen & Enghoff sp. nov.

urn:lsid:zoobank.org:act:8373DE9E-91BB-4F66-85AC-921DD8E2ADC6

Figs 20–21

Diagnosis

Differs from the other species of the genus by the combination of small size (width 4.1 mm), a slender postnodal telopodite, and lack of a bifid accessory process laterally on nodus. Virtually similar to A. kiellandi except for size and for having process C of the gonopod telopodite shorter and broader.

Etymology

The specific name is derived from the Latin ‘pusillus’, meaning ‘small’, and ‘kiellandi’, to emphasize the strong similarity with A. kiellandi , except for size.

Material examined

Holotype

TANZANIA • ♂; Iringa region /district, West Kilombero Scarp Forest Reserve ; 07°45′34.2″ S, 36°26′37.4″ E; 1510 m a.s.l.; 8 Dec. 2000; Frontier Tanzania leg.; plot Acacia , (open)woodland; NHMD 621683 .

Other material

TANZANIA • 1 ♀; same collecting data as for holotype; 5 Dec. 2000; NHMD 621684 .

Description

SIZE AND SHAPE. Body length 20.3 mm (approximate, specimen broken into several pieces). Maximum width 4.1 mm. W/L ratio 20 %.

COLOUR. After 18 years in alcohol without pigmentation ( Fig. 20 ).

BODY RINGS. Sternal process on ring 6 probably damaged, anterior edge very unevenly rounded and jagged ( Fig. 21H ). Apparently no transverse sternal carinae.

TELSON. Epiproct flattened at posterior end, forming a small, vertical flat surface with four protruding setae. Hypoproct semicircular with slightly triangular edge, paramedian tubercles large, extended beyond edge of sclerite. Setae on paraprocts protruding from distinct basal tubercles.

GONOPOD ( Fig. 21 A–G). Gonopod aperture suboval, extending back between second pair of legs on seventh ring, elevated in front of coxae, eliminated medially. Gonocoxa with paracannular setae. Prefemur with deep basal fossa on lateral side. Nodal process L present, process M absent. Processes A and B slender and curved, process C broader and longer than A and B. Processes B and C somewhat forcipulate in their curvature and position to each other. Postnodal telepodite slender and acuminate, slightly flattened, but not laminate as in A. mwanihana and A. harrisi . The right gonopod has a considerably higher number of small spikes and outgrowths than the left, and whereas process L on the left gonopod is slender and lance-shaped ( Fig. 21D ), on the right gonopod it is laminate and has a secondary tip halfway along its length ( Fig. 21E ). The angle between the prefemoral region and postnodal telepodite is almost 90° on the left gonopod, but the postnodal telopodite is more slanting posteriad on the right gonopod. The gonopods are almost identical to those of A. kiellandi , but nodal process C is shorter, broader and less curved in A. pusillokiellandi sp. nov. ( Fig. 21 ) than in A. kiellandi ( Hoffman 2005: fig. 451).

Distribution

Known only from the type locality, West Kilombero Scarp Forest Reserve, in the Udzungwa Mts, Tanzania.

Remarks

The right-left differences observed on the gonopods of the unique specimen of A. pusillokiellandi sp. nov. emphasize the desirability of having more than a single individual at hand when describing a new species, since with only one specimen it is impossible to estimate the level of intraspecific variation. Basing a new species on a single specimen which is almost identical to a known species (also known only from a single specimen), except for its body size, might seem ill-advised. The size difference in question, however, is dramatic: the width of the holotype of A. kiellandi is 2.1 times that of the holotype of A. pusillokiellandi sp. nov., corresponding to an almost tenfold volume difference. Large intraspecific size differences are not very frequent among polydesmidan millipedes, but there are some cases: in the Gomphodesmidae , the most variable species known to date is Astrodesmus laxus (Gerstäcker, 1873) in which male width varies from 6 to 15 mm. The smallest form was originally described as a separate species, A. petilus Cook, 1899 , but was ranked as a subspecies of A. laxus by Hoffman (2005). Other subspecies of A. laxus have male widths varying from 9.3 to 15 mm ( Hoffman 2005). Decker (2016, pers.comm.) found male width to range from 1.5 to 4.3 mm in Somethus castaneus (Attems, 1944) (Paradoxosomatidae) and from 2.1 to 3.4 mm in S. lancearius Jeekel, 2002 , in the latter case even within one small conservation park. Mesibov (2006, pers. comm.) found male widths between 1.2 and 1.8 mm in Lissodesmus hamatus Mesibov, 2006 (Dalodesmidae) and on https://myriapodology.org/ polydesmida /size.html he published a striking photo of two female L. hamatus , one a “dwarf”, the other a “giant”. Boyan Vagalinski (pers. comm.) has seen size differences on the same scale in Polydesmus mediterraneus Daday, 1889 (Polydesmidae) . We nevertheless choose to describe our small Agrophogonus as a new species, also being under the impression of the recent finding of two taxa of the genus Thyropygus Pocock, 1894 (family Harpagophoridae Attems, 1909 ) with identical gonopods, but of different sizes and molecularly sufficiently different to be regarded as separate species ( Pimvichai et al. 2011). The coexistence of several pairs of morphotypes, interpreted as species, of the genus Nepalmatojulus, Mauriès, 1983 (family Julidae Leach, 1814 ) with identical or extremely similar gonopods in the mountains of northern Thailand ( Enghoff 1987) also suggests that size plays an important role in millipede speciation.

Figures

Fig. 20. Agrophogonus pusillokiellandi Olsen & Enghoff sp. nov., holotype, ♂ (NHMD 621683). Scale bar: 5 mm.

Fig. 21. Agrophogonus pusillokiellandi Olsen & Enghoff sp. nov., holotype, ♂ (NHMD 621683). A–D, F–G. Left gonopod. A–B. Mesal view. C–D. Lateral view. F–G. Dorsal view. E. Right gonopod, lateral view. H. Sternal process on ring 6. Abbreviations: A = process A; B = process B; C = process C; L = process L. Scale bars: 0.5 mm.