Propyrgodesmus bulbogonopus, Aswathy & Sudhikumar, 2022

Aswathy, Mathilakath Dasan & Sudhikumar, Ambalaparambil Vasu, 2022, Review of the millipede genus Propyrgodesmus Silvestri, 1920, with the description of a new species from a sacred grove in Kerala, India (Diplopoda: Polydesmida Pyrgodesmidae), Zootaxa 5116 (4), pp. 591-599 : 593-597

Propyrgodesmus bulbogonopus sp. nov.

Figs 1–4

Material examined. Holotype ♂ (CATE-5503A), Sacred groves of Kottayil Siva Kshethram, Muchukunnu, Kozhikode district, Kerala, India 11°29’42’’N, 75°39’55’’E, 9 m a.s.l., collected from rotting wood, hand collection, 08.10.2021, M.D. Aswathy leg.

Paratypes: 1 ♂ (CATE-5503B), 2 ♀♀ (CATE-5503C, D), 3 ♀♀ juveniles (CATE-5503E, F, G), same locality, hand-collected together with holotype, but from top soil .

Name. To emphasize the bulbous appearance of the medial branch of the gonopodal telopodite.

Diagnosis. When comparing to P. lobulatus , the new species shows major differences in the tergal ornamentation by having most paraterga only vaguely trilobulate laterally ( Fig. 2B, E ), vs clearly trilobate ( Fig. 4A, B ) and by the presence of a ventral cone on antennomere 4 bearing a long sensillum trichodeum ( Figs 2C , 4G ), vs a ventral cone on antennomere 4 absent ( Fig. 4C ). On the contrary, the new species shows some similarities to the tergal ornamentation of P. frater , but differs significantly in the biramous gonopod with a bulbous lateral branch of the telopodite ( Fig. 3A, B ) vs with prong—and lobe-like structures on the main branch of the telopodite ( Fig. 4D, E ). A key to all three existing species of the genus is given below.

Description. Holotype ca 7.6 mm long, width of mid-body pro—and metazonae 0.78 and 1.5 mm, respectively. Male paratype ca 7.5 mm, width of pro—and metazonae 0.78 and 1.5 mm, respectively. Adult female paratypes ca 7.5 and 9 mm long, width of pro—and metazonae 0.76–0.85 and 1.5–1.6 mm, respectively. Live colouration dark brown, dorsum encrusted with soil particles; antennae, legs and venter pale whitish ( Fig. 1A, B ). Both vertex and frons light brown, clypeolabrum whitish ( Fig. 2A ).

Body broad due to large paraterga ( Fig. 1A ), with 20 body rings in both sexes ( Fig. 1A, B ). In width, head << collum ≤ 2 <3–16, body tapering thereafter towards telson ( Fig. 1A–C ). Head ovoid, slightly transverse and sparsely setose in clypeolabral region, granulate above antennal sockets either side of epicranial suture. Genae subquadrate and granulate. Interantennal isthmus twice as wide as diameter of antennal socket. Antenna short, weakly clavate, reaching up to body ring 3 when stretched ventrolaterally. In length, antennomere 7<6<1<3<4<2<<5 ( Figs. 2A, C , 4G ). Dense and sharply delimited fields of sensilla basiconica located distodorsaly on antennomeres 5 and 6. Sensory field of 5 th antennomere not extending up to base of long sensillum trichodeum.Antennomere 4 with ventral sensillum trichodeum borne on a small, but evident cone/hump ( Figs 2C , 4G ).

Collum flabellate ( Fig. 2A, B ), completely covering the head from above, fore margin with 5+5 distinct, subequal, faintly incised, rounded lobulations, middle with 4+4 distinct tubercles ( Fig. 2B ). Dorsum strongly convex, paraterga lying below mid-body height, moderately sloping down at about 20–25°. Tegument covered with a microspiculate cerotegument. Postcollum paraterga thick and rather indistinctly lobulated laterally ( Fig. 2B, E ), three lobulations on 2 nd and pore-bearing rings, vs two lobes on poreless ones ( Fig. 2B, E, F ). Pore formula: 5, 9, 12, 15, 17–19, ozopores borne on porosteles behind second lobulation of paraterga ( Fig. 2B ). All paraterga starting with 5 th directed caudad. Metaterga behind collum with 2+2 longitudinal rows of 3+3 larger and fused tubercles, those before ring 19 slightly inclined caudad. Paramedian tubercle on ring 19 abruptly modified to form an elongated ridge overhanging and concealing the epiproct ( Fig. 2E ). Epiproct directed ventrad, with four setae on top. Hypoproct triangular, caudal edge with two strong and well separated setae on knobs ( Fig. 2D ). Legs with neither adenostyles nor tarsal brushes, short, stout and enlarged, femur the longest ( Fig. 2G ). In length, femur> prefemur> tarsus> postfemur> tibia> coxa.

Gonopods taking up nearly entire ventral surface of metazonum 7, almost reaching the base of paraterga ( Fig. 2A ). Gonopods relatively simple, placed inside a transversely oblong gonopodal aperture, with thin and slightly elevated caudal and lateral margins. Both gonopods held parallel to each other, strongly exposed, telopodite tips directed caudally. Coxites (cx) voluminous, transverse and microgranulate laterally ( Fig. 3A, B ). Gonocoel distinct, but not too deep; telopodites short, simple, biramous and distally carrying a long, in situ caudally directed and slightly bifurcate lamina with fringed/microspiculate lamellae; solenomere (sl) slender and barely exposed; medial branch (b) stalked, with a short bulbous structure emerging distolaterally ( Fig. 3C, D ). A laminar sheath covering the postfemoral part of telopodite with a caudally directed hook-shaped/unciform tip (h) ( Fig. 3A, B ).

The following key can be proposed to separate the known species of Propyrgodesmus :

1 Sensillum trichodeum of the 4 th antennomere borne on a hump................................................. 2

- Sensillum trichodeum of the 4 th antennomere not on a hump........................................... P. lobulatus

2 Gonopod telopodite with a laterally directed prong-like structure.......................................... P. frater

- Gonopod telopodite with prominent bulb-like medial branch............................... P. bulbogonopus sp. nov.

Figures

FIGURE 1. Propyrgodesmus bulbogonopus sp. nov., habitus. A, C. Holotype ♂ (CATE-5503A), dorsal and ventral views, respectively. B. Female paratype (CATE-5503C), dorsal view. Scale bar: 1 mm.

FIGURE 2. Propyrgodesmus bulbogonopus sp. nov., paratype ♂ (CATE-5503B). A, B. Anterior part of body, ventral and dorsal views, respectively. C. Right antenna, anterior view. D–F. Posterior part of body, ventral, dorsal and lateral views, respectively. G. Right midbody leg, anterior view. Scale bars: 0.5 mm (A, B, E), 0.4 mm (D), 0.2 mm (C), 0.1 mm (F, G).

FIGURE 3. Propyrgodesmus bulbogonopus sp. nov., paratype ♂ (CATE-5503B). A. Left gonopod, posterior view. B. Right gonopod, anterior view. C, D. Both gonopods, posterior and anterior views, respectively. Abbreviations: b: medial branch; cx: coxite; h: hook like structure of telopodite; sph: solenophore; sl: solenomere. Scale bar: 0.2 mm (for C and D). A, B not to scale.

FIGURE 4. Propyrgodesmus spp. A–C. Propyrgodesmus lobulatus Silvestri, 1920, holotype ♀ after Silvestri (1920). A, B. Anterior and posterior parts of the body, dorsal and lateral views, respectively. C. Right antenna, anterior view. D–F. Propyrgodesmus frater Carl, 1932 syntype ♂, after Carl (1932). D, E. Gonopods, anterior and posterior views, respectively. F. Antenna. G. Propyrgodesmus bulbogonopus sp. nov., holotype ♂ (CATE-5503A), right antenna, anterior view. Not to scale.