Gnomognathus macracanthus ( Carl, 1941 )

Sudhakaran, Nikhila & Kuruvila, Manju Elizabeth, 2025, A new millipede species of the genus Gnomognathus Attems, 1942 (Diplopoda, Spirostreptida, Harpagophoridae) from South India, Zootaxa 5659 (3), pp. 335-356 : 345-347

Gnomognathus macracanthus ( Carl, 1941)

Fig. 7

Material examined. 1 male, Dhoni (10°47.934’N, 76°45.610’E), Palakkad, Kerala, 02 September 2024, hand-collected by Nikhila Sudhakaran (RDZ-ACP-SS206) .

Diagnosis. The anterior coxal fold (AC) of G. macracanthus ( Fig. 7A, B ) is most similar to that of G. minusculus ( Fig. 9B ) in overall shape but differs from it mainly by the small mesal process (mp), a triangular ridge on the posterior surface along paramedian process (pp), and a long, distally rounded antero-lateral process. Posterior coxal fold (PC) with a downward-directed sub-distal mesal spine (in G. minusculus anterior coxal fold with a well-developed mesal process spiny at the end, triangular ridge on posterior surface absent, and antero-lateral process long but tapering and spiny; mesal spine on posterior coxal fold absent). Telopodite differs from all the congeners by the presence of lamellate lobes (ll) and the translucent, spine-like projections and a dense covering of fine setae on one of them. Telopodite is most similar to that of G. interfectus ( Fig. 9D ) by the absence of femoral spine, presence of tibial spines (ts) placed on a projection, and apical part branched and lobed with a broad palette. Differs from G. interfectus in that four stout tibial spines (ts) are on a bulge-like projection, additional spines absent, and the second branch consists of two lamellate lobes (in G. interfectus , three curved tibial spines present on a hemispherical projection, additional spines present on palette, and the second branch not lobed).

AC of G. macracanthus ( Fig. 7A, B ) is also similar to that of G. nanus ( Fig. 9A ) in overall shape but differs from it in the same ways it differs from G. minusculus (in G. nanus anterior coxal fold with a pointed mesal process, triangular ridge on the posterior surface absent, and antero-lateral process not long but folded forward; mesal spine on posterior coxal fold absent).The apical part of telopodite like G. nanus is trilobed, but the telopodite is without a femoral spine and apical part branched; in G. nanus telopodite with a femoral spine and an unbranched apical part. Differs from the tricolor group ( G. tricolor , G. eremitus , and G. vicarius ) ( Fig. 10A–C ) and G. helicogonus ( Fig. 10D ) mainly by the absence of a well-developed mesal process, presence of a triangular ridge on posterior surface, long antero-lateral process, and absence of the indentation and baso-lateral process on the lateral margin of AC (in tricolor group and G. helicogonus anterior coxal fold with a well-developed mesal process, triangular ridge absent on posterior surface, antero-lateral process comparatively not developed, and the lateral margin with deep indentation followed by a baso-lateral process; presence of the indentation and baso-lateral process not definite in G. nanus ( Fig. 10B )). Telopodite differs from that of the tricolor group by the absence of a femoral spine and presence of four tibial spines (ts) on a bulge-like projection; apical part branched, and palette (pa) without a serrated border (in the tricolor group, a femoral spine present, and two tibial spines present, placed on the telopodite inner and outer surfaces in G. tricolor and on the outer surface in G. eremitus ( Fig. 10A, C ), or tibial spines completely absent as in G. nanus ; apical part simple, terminating in the palette with a serrated border). Telopodite differs from that of G. helicogonus by the branched and lobed apical part without any additional spines; in G. helicogonus apical part neither branched nor lobed, and palette with additional spines.

Descriptive notes. Color in alcohol overall light grey with yellowish-brown margin and yellow dorsal mesal spot; toward the ventral side, body dull white. Length ca. 58.5 mm, width ca. 2.5 mm, body rings 51 podous rings + telson. Five supralabral foveolae. Mandibular stipites without hook-like ends. Legs without longitudinal depressions on prefemur and femur. Weak pads on postfemur and tibia restricted to legs towards the anterior end. Preanal process curved downward and pointed.

Gonopods. Anterior coxal fold (AC) with three processes: mesal process (mp) small, paramedian process (pp) with a longitudinal triangular ridge on the posterior surface, and antero-lateral process (alp) long and curved backward. Posterior coxal fold (PC) with a sub-distal mesal spine directed downward; triangular postero-lateral process (plp) and baso-lateral process (blpPC) present ( Fig. 7A–C ). Telopodite without femoral spine. Free part of the telopodite short and complex, with four stout tibial spines (ts) on a bulge-like projection that continues with the palette (pa). Apical part split into two branches: pa bulged outward, with a row of xyrochaetae (xc) (ca. 16), of which few are bifurcated; the second branch with two lamellate lobes (ll). The larger ll is closer to the pa with a dense covering of fine setae and translucent, spine-like marginal projections (also with setae). Smaller ll attached to the larger ll and appears smooth ( Fig. 7D, E ).

Notes. A transparent region is present on the anterior coxal fold.

Remarks. This new specimen may represent a third form of G. macracanthus , as Carl (1941) had suggested. All three forms of G. macracanthus are each described based on a single specimen. The anterior coxal fold (AC) of the new specimen ( Fig. 7A, B ) differs from both Form A ( Fig. 9E ) and Form B ( Fig. 9C ) of G. macracanthus by the presence of a downward-directed sub-distal mesal spine, a longitudinal triangular ridge (tr) on the posterior surface of the paramedian process (pp), long antero-lateral process (alp), and the absence of any additional process on the lateral margin (both forms with an additional lateral process). Telopodite ( Fig. 7D, E ) is similar to that of both forms by the presence of tibial spines (ts) on a projection. Differs from both forms in that the four ts are placed together on a bulge-like projection and additional spines (as) are absent; in both forms, the two tibial spines are placed on an elbow-like projection and additional spines present. The apical part of telopodite, like Form B, is lobed and consists of lamellate lobes (ll) with a dense covering of fine setae and translucent, spine-like marginal projections on one of the lobes; it differs from Form B in that the palette (pa) is broader and not narrow and tapering like Form B, and the number of ll is two and not three as in Form B. Further sampling is needed to confirm whether differences represent consistent morphological forms.

Figures

FIGURE 7. Gnomognathus macracanthus, gonopods (RDZ-ACP-SS206). A. Rightgonopod without telopodite, anterior view. B. Right gonopod without telopodite, posterior view. C. Right gonopod with telopodite, posterior view. D. Right telopodite, mesal view. E. Right telopodite, lateral view. Abbreviations. AC: anterior coxal fold; alp: antero-lateral process; blpPC: basolateral process of posterior coxal fold; ll: lamellate lobes; mp: mesal process; pa: palette; pp: paramedian process; plp: posterolateral process; px: paracoxite; tr: triangular ridge; ts: tibial spines; xc: xyrochaetae. Scale bars = 1 mm.

FIGURE 9. Gonopods of previously described Gnomognathus species. A. G. nanus (Carl, 1941). B. G. minusculus (Attems, 1936). C. G. macracanthus (Carl, 1941) (Form B). D. G. interfectus (Carl, 1941). E. G. macracanthus (Carl, 1941) (Form A) (Figures reproduced from Attems (1942) and Carl (1941)).

FIGURE 10. Gonopods of previously described Gnomognathus species. A. G. tricolor (Carl, 1941). B. G. vicarius (Carl, 1941). C. G. eremitus (Carl, 1941). D. G. helicogonus (Carl, 1941) (Figures reproduced from Carl (1941)).