Otostigmus spinosus Porat, 1876

Siriwut, Warut, Edgecombe, Gregory D, Sutcharit, Chirasak & Panha, Somsak, 2014, Brooding behaviour of the centipede Otostigmus spinosus Porat, 1876 (Chilopoda: Scolopendromorpha: Scolopendridae) and its morphological variability in Thailand, Raffles Bulletin of Zoology 62, pp. 339-351 : 345-348

Otostigmus spinosus Porat, 1876

( Figs. 5 , 6 )

Otostigmus spinosus Porat, 1876: 22 Branchiotrema nitidulum Tömösváry, 1885: 26 , table 3, figs. 19, 20 Otostigmus spinosum: Haase, 1887: 71 , Taf. 4, fig. 70a–d Otostigmus spinosum ab. hirtipes Haase, 1887: 71, Taf. 4, fig. 71a–c Otostigma spinosum: Pocock, 1891b: 414 ; Pocock, 1894: 312 Otostigmus spinosus: Kraepelin, 1903: 116 , fig. 53; Kraepelin,

1904: 247; Attems, 1930a: 152, fig. 182; Attems, 1930b: 118;

Verhoeff, 1937: 212; Chamberlin, 1939: 3; Chamberlin, 1944:

1; Lewis, 1991: 340, figs. 11–14; Khanna, 1994: 467; Lewis,

2001: 37, figs. 75–78; Khanna, 2001: 206; Schileyko, 2007:

81, fig. 5; Lewis, 2010: 6, figs. 8–13 nec Otostigmus (O.) spinosus: Lewis, 1982: 365 , figs. 25–31; Lewis,

1984: 37, fig. 3.15

Type locality. Indonesia: Java .

Distribution. Java, Sumatra, New Guinea, Burma, Laos, Thailand, Vietnam, Malaysia, India?

Material examined. Malaysia: BMNH 1898.9.15.75–76 general collection, 2 of 3 specimens in tube labeled “ Otostigmus sp. ” from Penang . Laos: CMUZ 00232 , one specimen from Ban Kra- Som, Attopue , Laos (15°0'27.2" N 106°51'14.6" E) . Thailand: CUMZ 00224 , one specimen from Wat Tham Wararam, Phanom district , Surat Thani (8°53'2.7" N 98°40'1.4" E) . CUMZ 00228 , two specimens from Khao Sok, Phanom district , Surat Thani (8°53'37.3" N 98°33'107" E) . CUMZ 00225 , five specimens from Wat Kerewong, Thap Put district, Phang-nga (8°31'54.8" N 98°34'37.8" E) . CUMZ 00226 , one specimen from Sairung waterfall, Takua Pa district, Phang-nga (8°44'28.3" N 98°16' 43.1" E) . CUMZ 00231 , 53 specimens from Surin islands, Phang-nga (9°26'41" N 97°53'30.3" E) . CUMZ 00230 , one specimen from Sichon district , Nakhon Si Thammarat (9°5'31.4" N 99°54'23.2" E) . CUMZ 00229 , three specimens from Tham Wang Thong, Khuan Khanun district , Phatthalung (7°40'53.5" N. 100°0'56.6" E.) . CUMZ 00223 , one specimen from Tham Sumano, Srinagarindha district , Phatthalung (7°35'11.9" N 99° 52'3.2" E) , CUMZ 00227 , one specimen from Huaito waterfall, Khao Phanom district , Krabi (8°13'35.5" N 98°53'2.5" E) .

Diagnosis. 17–22(24) antennal articles, basal 2.3–2.8 articles glabrous dorsally. Forcipular coxosternum with 4–6 main teeth. Forcipular trochanteroprefemoral process with one apical and two inner teeth. Tergite surface smooth, without keels, but with scattered small spines or setae; paramedian sutures starting from TT4–7 and complete margination from TT7–15. Tergite of ultimate leg-bearing segment with or without depression. Sternites with incomplete paramedian sutures occupying 10–30% of anterior part of sternite, posterior part with shallow depression. Posterior margin of sternite of ultimate leg-bearing segment concave, lateral margins converging. Coxopleural process with one to three apical spines, one sub-apical or none, one lateral or none, and one dorsal spine. Ultimate legs long and slender, spine formula on prefemur VL-4 or 5, VM-2–4, M-2–5 and DM- 1–4 (including corner spine). Locomotory legs with two accessory spurs; legs 1–3 to 1–5 in equal frequency (rarely 2, 6 or 7) with two tarsal spurs, legs 5–21 (rarely 3, 7 and 8) with one tarsal spur. One tibial spur on legs 1–3 (rarely leg 4). Femoral spur only on leg 1. Dorsal side of leg 20 with one spine at end of prefemur.

Description. Maximum body length approximately 38 mm. Body colour of living animal greenish black except tergite of ultimate leg-bearing segment, which is reddish black. Trochanteroprefemur yellowish white or light brown. Legs light blue or purple except prefemur, which is light yellow. Cephalic plate without sulci or sutures. Preserved specimens dark purple.

Antennae with 17–22 articles ( Fig. 5C ), 24 articles in one specimen. Basal 2.5–2.8 articles glabrous dorsally ( Fig. 6B ); atypically 2.3. Basal 2.5–2.8 articles glabrous ventrally ( Fig. 6A ). Antennae reach segments 4–6 (5 or 6 in large specimens). Forcipular trochanteroprefemoral process bearing one apical and two inner teeth (rarely 3; see Figs. 6D–E ). Coxosternal tooth plate wider than long with 4, 5 or 6 main teeth in equal frequency (rarely 3 or 7; see Fig. 6C–F ), separated into two groups; inner three or four teeth usually fused and outer 1 or 2 acute ( Figs. 5B , 6C, 6F ), basal part with one transparent, fine seta on each side, atypically with 1 transparent spine and 2 small spines in a depression ( Fig. 6F ). One specimen shows an abnormal condition with both tooth plates fused together ( Fig. 6D ). Coxosternum lacking median suture in some specimens ( Fig. 6D ), median diastema reaching to base of tooth plate, connecting with basal oblique sutures ( Fig. 6C, 6E, 6F ). Angle of basal oblique sutures ca 105–110°. Telopodite 2 of second maxilla with one strong transparent spine on each side.

First tergite overlapping cephalic plate, without transverse sulcus ( Fig. 5A ). Tergites with paramedian sutures complete from TT5 to 6 (rarely TT7); margination typically starting on TT11 to 15 (atypically TT9–10). Tergite surface ( Figs. 5D , 6G ) with oblique suture anteriorly on TT3 to 5 and with paramedian sulci on TT3 or 4 to 18 (to TT 19 to 20 in large specimens). Tergite of ultimate leg-bearing segment ( Fig. 6L ) usually with median furrow on posterior part (rarely absent). Sternites ( Fig. 5E ) with short paramedian sutures on anterior part, occupying 10–30% length of sternite. Surface of some sternites with small scattered setae and depressions grouped in triangular arrangement (one atypical specimen with depression continued behind end of paramedian suture), all mostly found on posterior part of sternite ( Fig. 6H ). Sternite of ultimate leg-bearing segment ( Fig. 6K ) with sides converging posteriorly, posterior margin concave (one specimen with depression on surface). Oval spiracles present on segments 3, 5, 8, 10, 12, 14, 16, 18 and 20 ( Fig. 5F–H ). Coxopleural process moderately long with two apical spines (rarely 1 or 3), one subapical spine or none, one to two lateral spines or none, and one dorsal spine or none ( Fig. 5I ). Coxopleura with dense pore field covering whole area except on ventro-distal part of coxopleural process ( Figs. 5J , 6M ), pore-free area on coxopleural process extending 50–70% length from distal part to the margin of sternite of ultimate leg-bearing segment ( Fig. 5I ). Ultimate legs long and slender with ratios of lengths of prefemur and femur 6:4, tibia and tarsus 2 1.5:1; tarsus 1 and tarsus 2 03:2. Prefemoral spines in four rows ( Fig. 5K–L ), formula VL-4–5 (rarely 2, 6 and 7), VM-3–4 (rarely 1 or 2), M-2–5 (usually 4), DM-1–4 including corner spine (rarely 5 or 6).

Locomotory legs with or without short setae, usually legs 1–5 with two tarsal spurs (rarely 1–2 or up to 6 and 7), the subsequent legs to 21 with one tarsal spur. One tibial spur on legs 1–2 or 3 in equal frequency (rarely 1–4). Leg 1 with femoral spur (rarely absent). Two accessory spurs and pretarsal claw present on all legs. Dorsal part of prefemur of leg 20 with one spine ( Fig. 5M, N ) at the margin of prefemur (atypically found only on one side). Anterior face of leg 20 in some males with a short, rounded, variably depigmented projection on distal end of tarsus 1 ( Fig. 6I ); similarly proportioned projection on tarsus 1 of leg 21 in two of four specimens with a projection on leg 20; projections most strongly developed in the largest specimen ( Fig. 6J ).

Remarks. The taxonomic status of O. spinosus and O. punctiventer Tömösváry, 1885 is still unclear, the two species possessing the synapomorphic character of a distal prefemoral spine on leg 20. In this study, we found that the range of variation of some taxonomic characters in O. spinosus to overlap with the description of O. punctiventer sensu Lewis, 2010 (see Table 2). Moreover, the geographic distributions of O. punctiventer and O. spinosus overlap at least on peninsular Malaysia. For these reasons, the identification based on morphology of O. spinosus and O.punctiventer is complicated and needs to be reassessed. The nominate subspecies of O. spinosus is recognised in this work; O. spinosus spinosus Porat, 1876 and O. spinosus nannus Chamberlin, 1939 are currently valid subspecies, though the latter has been questioned as possibly being based upon a juvenile specimen of Ethmostigmus rubripes spinosus ( Newport, 1845) ( Schileyko & Stagl, 2004). The type locality of O. spinosus nannus is Doormanpad, Irian Jaya/West Papua (New Guinea). We found one specimen of Otostigmus in the NHM from Mimika River, Irian Jaya, that we identified as O. spinosus but its associated label indicated affinities to O. punctiventer .

In Thailand, O. spinosus is widespread throughout the southern part of the country ( Fig. 1 ). In all localities this species was found together with other Otostigmus species such as O. multidens , O. rugulosus , O. astenus , and O. scaber . As some taxonomic characters, such as the range of appearances of tibial and tarsal spurs on the locomotory legs, number of antennal articles, and numbers of apical and lateral spines on the coxopleural process are variable ( Table 1), there can be problems in determining species. On some occasions we found animals in which the spine on the prefemur of leg 20, a diagnostic character, was absent on one side. The characteristic of leg 20 (and variably 21) bearing a distal projection on the anterior face of tarsus 1 is apparently unique to this species and, with the data at hand, appears to be a secondary sexual characteristic. The three specimens possessing this feature that exhibit the genital segments are all males and its elaboration with growth is consistent with it being sex-specific. Other Otostigminae have distal processes on different articles of the ultimate leg-pair in males, e.g., on the inner side of the femur in Digitipes Attems, 1930 , and on the inner side of the tibia in Otostostigmus (Parotostigmus) tibialis Brölemann, 1902 . The inconsistency of taxonomic characters may be problematic when it involves the purported diagnostic characters of species and may lead to misidentifications. Molecular data could assist with revaluating species delimitation in the Otostigmus rugulosus group (sensu Lewis, 2010).

Variation and development of taxonomic characters. In this study, we found two broods that belong to adolescent stages that permitted investigating the development of some taxonomic characters. In hatchlings in brood D, an early first adolescent stage, most taxonomic characters are incompletely developed. Contrastingly, in the four surviving hatchlings of brood A, some taxonomic characters (including some species-diagnostic characters) are fully developed. Our observations reveal that some traditional taxonomic characters such as number of antennal articles, number of glabrous articles, and number of apical spines on the ultimate leg coxopleuron vary during the life span. A distinguishing character of this species (the prefemoral spine on leg 20) is strongly fixed, being conserved between the mother and second adolescent stage hatchlings except in one specimen (see Table 2) presumably due to abnormal development. Colouration differs between young and the mother; hatchlings show a very light yellowish or brown and magenta colour whereas mothers are dark greenish brown.

Figures

Fig. 5. Otostigmus spinosus Porat, 1876. Light photographs of specimens from southern Thailand (Fig.A–E; specimens from Surin Islands, Phang-nga province: CUMZ 00231; Fig. I–N; specimens from Wat Tham Wararam, Surat Thani province: CUMZ 00224). A, Cephalic plate and T1 with first pair of locomotory legs; B, Forcipular segment; C, Antenna with cephalic plate and TT1–5; D, Tergites 9–10; E, Sternites 9–10; F–H. Spiracles on segments 3, 5 and 8, respectively; I, Tergite and sternite of ultimate-leg bearing segment; J, Pore field on left and right coxopleura; K, Dorsal view of ultimate leg prefemur; L, Ventral view of ultimate leg prefemur; M–N, Leg 20 left and right with spine on distal part of prefemora.

Fig. 6. Variability in taxonomic characters in Otostigmus spinosus Porat, 1876 (examination materials: CUMZ 00224, Wat Tham Wararam, Phanom district, Surat Thani; CUMZ 00229, Tham Wang Thong, Phatthalung; CUMZ 00231, Surin Islands, Phang-nga). A, Ventral view of cephalic plate and antenna; B, Dorsal view of cephalic plate and antenna; C, Coxosternite; D–F, Variation in coxosternal teeth; G, Surface of TT5–7; H, Variability of depressions on surface of sternites 5–7; I, Leg 20 with projection on distal end of tarsus 1; J, Leg 21 with projection on tarsus 1; K, Ultimate leg-bearing segment, ventral view, with arrangement of ventral spines on prefemur of ultimate legs; L, Tergite of ultimate leg-bearing segment with arrangement of dorsal and corner spines on prefemur of ultimate legs; M, Pore field on coxopleuron (left).

Fig. 1. Distribution of Otostigmus spinosus Porat, 1876 in southern Thailand.