Gnomognathus Attems, 1942

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 : 336-347

Genus Gnomognathus Attems, 1942

Type species. Thyropygus minusculus Attems, 1936 , by original designation.

Description. Based on relevant literature ( Attems 1936, 1942; Carl 1941). Species with a diameter ≤ 4 mm. Head smooth, shiny, without interocular groove. Antennae short and compressed. Eyes not touching antennal sockets. Supralabral foveolae variable: 2+2, 3+3, 5. Three labral teeth. Mandibular stipites laterally flat with inwardly curved, hook-like ends. Mentum pit deep. Stipites of gnathochilarium with a distal bump. Collum anterior corner rounded, posterior corner blunt; antero-lateral margin with narrow, flat thickening widened only at the corner. Prozonites with transverse striations. Metazonites smooth, with lateral longitudinal striations not reaching the pore level. Transverse suture sharp. Ozopores starting from 6 th body ring placed laterally on metazonites, closer to transverse suture. Sternites with transverse striations; posterior striations more prominent than anterior striations. Stigmatic cavity small. Legs with longitudinal depressions on prefemur and femur. Weak pads on postfemur and tibia. Prefemur of first pair of legs either extended outward into a rounded lobe or sub-rectangular with a distinct fold on it. Preanal process short, straight, and blunt. Subanal scale long, broadly curved. Margin of anal valve thick, bordered by shallow depression.

Gonopods. Anterior coxal fold modified with different processes. Distal processes: mesal process elaborate, apical, innermost, formed by fusion of distal and mesal margins, curved inward or backward, usually spiny at the end; paramedian process intermediate between mesal and antero-lateral process; antero-lateral process, distalmost, occasionally bent backward. Lateral margin with or without a lateral process. Anterior coxal fold with or without a transverse ridge. Posterior coxal fold with lateral and basal processes. Telopodite with single femoral spine and tibial spines. Apical part of telopodite mostly lobed, with one lobe forming the palette. Telopodite palette with xyrochaetae, occasionally with serrated border and additional spines ( Attems 1936, 1942; Carl 1941).

Diagnosis. Gnomognathus differs from other genera of the tribe Harpurostreptini by the absence of a mesal notch separating the anterior and posterior coxal folds apically. Instead, the coxal folds are fused along the mesal margin and partially along the distal margin to form the mesal process. Gnomognathus differs from the genus Carlogonus by the distal processes of the anterior coxal fold, especially the mesal process, and the absence of a mesal spine on the lateral margin of the anterior coxal fold. Telopodite with shorter tibial spines placed variably on it and a wide, mostly lobed apical part of the telopodite (in Carlogonus , anterior coxal fold with a small hook on the anteromesal margin and an additional mesal spine on the lateral margin; telopodite with mostly longer and curved tibial spines; and the apical part of the telopodite is slender, unbranched, and very rarely lobed). Differs from the genus Harpurostreptus by the distal and lateral processes of the anterior coxal fold and the shorter, non-spiraled, mostly lobed apical part of the telopodite (in Harpurostreptus , the anterior coxal fold is near-triangular, with unmodified margins except for a pointed antero-lateral tip; telopodite long, spirally twisted with several small spines arranged on the inner surface, and the apical part neither lobed nor branched). It differs from genus Organognathus by the absence of a strong mesal spine on the posterior coxal fold; telopodite with a femoral spine and apical part of the telopodite mostly lobed (in Organognathus , posterior coxal fold with a strong downward-directed mesal spine; femoral spine absent, apical part of the telopodite branched with one branch carrying the seminal groove). Differs from the genus Janardananeptus in the overall structure of anterior and posterior coxal folds and by the absence of an additional lobe between the two coxal folds. Apical part of the telopodite mostly lobed with xyrochaetae and additional spines on the palette (in Janardananeptus , an additional lobe present between the two coxal folds; apical part of the telopodite branched with delicate hair-like structures and translucent spines ( Attems 1936, 1942; Carl 1941; Demange 1961, 1977a, 1977b, 1982, 1983, 1989; Sankaran & Sebastian 2020; Verhoeff 1936, 1938).

Distribution. South India ( Fig. 8 ).

Key proposed to Gnomognathus spp. based on male features

(Mainly based on characters defined by Attems (1936, 1942) and Carl (1941), see Figs 9 and 10 ).

1. Apical part of telopodite simple, with or without marginal lobe................................................. 2

- Apical part of telopodite branched and lobed................................................................ 8

2. Apical part of telopodite with a marginal lobe, without additional spines, palette with a serrated border................. 3

- Apical part of telopodite without a marginal lobe, with or without additional spines, palette without a serrated border...... 6

3. Anterior coxal fold with a well-developed and elaborate mesal process, transverse ridge greatly reduced or absent; telopodite with tibial spines...................................................................................... 4

- Anterior coxal fold with a well-developed but simple mesal process, transverse ridge strong; telopodite with or without tibial spines.............................................................................................. 5

4. Anterior coxal fold expanding distally, mesal process streamlined with a pointed tip, antero-lateral process extended backward, transverse ridge absent; telopodite with a large femoral spine, two tibial spines placed on the inner and outer surface of telopodite.......................................................................... G. tricolor ( Fig. 10A )

- Anterior coxal fold slender, mesal process strongly downward-directed with a hooked tip, antero-lateral process blunt, transverse ridge greatly reduced; telopodite with a weak femoral spine covered by a protective flap, two tibial spines placed parallel on the outer surface of telopodite............................................................. G. eremitus ( Fig. 10C )

5. Anterior coxal fold with a strongly rounded mesal process with a small prong, antero-lateral process not prominent, transverse ridge strongly developed; telopodite without tibial spines..................................... G. vicarius ( Fig. 10B )

- Anterior coxal fold with a beaked and spiny mesal process, antero-lateral process extended backward, semicircular transverse ridge present; telopodite with two tibial spines........................................ G. dhoni sp. nov. ( Figs 2–4 )

6. Telopodite with a short, blunt femoral spine, with a single tibial spine; apical part trilobed with one pointed and two rounded lobes; pointed lobe forms the palette, additional spines absent.................................... G. nanus ( Fig. 9A )

- Telopodite without a femoral spine, with two tibial spines; apical part without additional lobes, additional spines present... 7

7. Anterior coxal fold with mesal process divided into two conical prongs, baso-lateral process hook-like and bent backward; telopodite spirally twisted, two tibial spines on the inner surface; small additional spines present on the palette........................................................................................... G. helicogonus ( Fig. 10D )

- Anterior coxal fold with mesal process having a notched edge and a pointed spine hanging backward, baso-lateral process absent; telopodite not spirally twisted, two tibial spines on an elbow-like projection; longer additional spines present basal to the palette................................................................ G. macracanthus Form A ( Fig. 9E )

8. Apical part of telopodite with lamellate lobes, marginal spine-like projections, and fine setae present on one of the lobes... 9

- Apical part of telopodite without lamellate lobes or marginal spine-like projections and fine setae..................... 10

9. Anterior coxal fold with a small mesal process, triangular ridge present on posterior surface, additional process on lateral margin absent; posterior coxal fold with a downward-directed mesal spine; telopodite with four tibial spines on a bulge-like projection; apical part without additional spines, palette broad................. G. macracanthus (new specimen) ( Fig. 7 )

- Anterior coxal fold with a strong, lamellate, and hook-like mesal process, triangular ridge absent, additional process on lateral margin present; posterior coxal fold without any spine; telopodite with two tibial spines on an elbow-like projection; apical part with additional spines basal to the palette, palette narrow and tapering................ G. macracanthus Form B ( Fig. 9C )

10. Anterior coxal fold with mesal process extended to form a spiny tip, antero-lateral process long and tapering with a spiny tip, triangular ridge on posterior surface of anterior coxal fold absent; telopodite with a femoral spine, a single tibial spine present; palette without additional spines....................................................... G. minusculus ( Fig. 9B )

- Anterior coxal fold with mesal process hook-like and strongly bent backward, antero-lateral process narrow, greatly elongated and bent backward, triangular ridge on posterior surface of anterior coxal fold present, telopodite without a femoral spine, three tibial spines present on a hemispherical projection; palette with additional spines................ G. interfectus ( Fig. 9D )

Figures

FIGURE 2. Gnomognathus dhoni sp. nov., gonopods (paratype males, RDZ-ACP-SS201). A. Left gonopod without telopodite, anterior view. B. Right gonopod with telopodite, posterior view. C. Left gonopod without telopodite, posterior view. D. Right gonopod without telopodite, mesal view. Scale bars = 0.3 mm.

FIGURE 3. Gnomognathus dhoni sp. nov., telopodite (paratype males, RDZ-ACP-SS201). A. Right telopodite with broken femoral spine, posterior view. B. Left telopodite with broken base, anterior view. C. Apical part of telopodite, inner side. D. Apical palette, outer surface. Scale bars: A, B = 0.2 mm; C = not to scale; D = 0.4 mm.

FIGURE 4. Gnomognathus dhoni sp. nov., gonopods (paratype male, RDZ-ACP-SS201).A. Gonopods with telopodite, anterior view. B. Gonopods with telopodite, posterior view. C. Left gonopod without telopodite, posterior view. D. Left telopodite, posterior view. E. Left telopodite, anterior view. Abbreviations. AC: anterior coxal fold; alp: antero-lateral process; blpAC: baso-lateral process of anterior coxal fold; blpPC: baso-lateral process of posterior coxal fold; fs: femoral spine; ml: marginal lobe; mp: mesal process; pp: paramedian process; PC: posterior coxal fold;; plp: postero-lateral process; px: paracoxite; sb: serrated border; sg: seminal groove; tr: transverse ridge; ts1: tibial spine 1; ts2: tibial spine 2; xc: xyrochaetae. Scale bars = 1 mm.

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 8. Known distribution of Gnomognathus species based on literature and new records.

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)).