Digitipes Attems, 1930

Lewis, John G. E., 2015, On Verhoeff’s Otostigmus subgenus Malaccopleurus, the nudus group of Otostigmus subgenus Otostigmus Porat, 1876, and Digitipes Attems, 1930, with a description of the foetus stadium larva in O. sulcipes Verhoeff, 1937, (Chilopoda: Scolopendromorpha: Scolopendridae), Zootaxa 4039 (2), pp. 225-248 : 243-245

Genus Digitipes Attems, 1930

Introductory remarks. Digitipes is considered here, as two of the putative eleven species of the genus are very similar to two Otostigmus species discussed in this paper.

Attems (1930a, b) characterised the genus by the presence of a process on the femur of the ultimate legs in males and the second maxillary pretarsus without accessory spines and without a spur on article 2 of the telopodite. Lewis (2004) pointed out that the accessory spines could be very rudimentary in some Otostigmus species and that the spur was absent in O. resrevatus Schileyko, 1995 . Furthermore Chagas-Jr. et al. (2007) did not observe accessory spines or a spur on article 2 of the telopodite in seven South American species of Otostigmus (Parotostigmus) confirming that there is no justification in the separation of Digitipes from Otostigmus . Most recently, Joshi & Edgecombe (2013) showed that these characters were present in Indian Digitipes . They agreed that the two peculiarities of the second maxilla cited by Attems (1930a, b) as diagnostic for Digitipes are of no value for the generic concept if it is meant to encompass Indian species. See Joshi & Edgecombe (2013) for a full discussion of the matter.

Joshi & Edgecombe (2013) defined the genus as Otostigmini lacking spiracle on segment 7. Forcipular toothplates with four teeth, the inner two grouped. Coxopleural process with two apical spines, no dorsal spines, single lateral spine present or absent. Conical to subcyclindrical distomedial process on femur of ultimate leg in male, longitudinal furrow along medial surface of femur terminating on the process. However, they pointed out that apart from the characters of the male ultimate leg, these characters are shared by other species currently assigned to Otostigmus (Otostigmus) and this is true for all the species of Otostigmus considered here.

The African Digitipes species

( Table 3 )

Of the three African species, Digitipes verdascens Attems, 1930 , the type species, and D. reichardti ( Kraepelin, 1903) have a distomedial process on the ultimate leg femur in the male but the sole specimen of D. krausi Dobroruka, 1968 , lacks this process and was described as a female. Dobroruka assigned it to Digitipes as the second maxillary telopodite lacked pretarsal accessory spines and a spur on article 2, as he indicated in a table showing the characters of Digitipes . As noted above, these are of no value in distinguishing the genus from Otostigmus .

Digitipes krausi and the other two African species are similar in that only the tergite of the ultimate leg-bearing segment is marginate (this is also listed as a character of Digitipes by Dobroruka). However, it differs from them in other respects, resembling O. cuneiventris in the absence of sternite paramedian sutures and the presence of sternite depressions. In D. krausi there are three depressions (Dobroruka’s Fig. 16 ), closely resembling in size and arrangement the larger three in O. cuneiventris spm 1 from Mapanja, Cameroon ( Fig. 52 ). It also differs from the other two Digitipes species in that the legs lack tarsal spurs and the presence of three rows spines on the prefemoral of the ultimate legs (VL 3, VM 2, DM 2) rather than two ( Table 3 ). Its assignment to Digitipes thus rests solely on the fact that only the ultimate leg-bearing tergite is marginate but this character is seen in other Otostigmus species namely the North African O. spinicaudus ( Newport, 1844) and the East African O. tanganjikus Verhoeff, 1941 , both of which, unlike D. krausi , have most legs with tarsal spurs. I conclude that D. krausi is an Otostigmus and thus becomes Otostigmus krausi ( Dobroruka, 1968) comb. nov.

The Indian Digitipes species

( Table 4 )

Joshi & Edgecombe (2013) resolved the nine putative species of Indian Digitipes recognised by Joshi & Karanth (2012) in a molecular analysis as five Digitipes species and Otostigmus ruficeps Pocock, 1890 . The Digitipes species are Jangi & Dass’s (1984) D. barnabasi , D. coonoorensis and D. indicus and two new species: D. jangii Joshi & Edgecombe (2013) and D. periyarensis . They showed that D. indicus is a junior subjective synonym of Arthrorhabdus jonesii Verhoeff, 1938 , the combination becoming Digitipes jonesii ( Verhoeff, 1938) . They accepted the validity of D. pruthii Jangi & Dass, 1984 , and D. chhotanii Jangi & Dass, 1984 , although these species were known only from single specimens.

Joshi & Edgecombe (2013) noted that D. periyarensis ( Joshi & Karanth’s (2012) Digitipes putative species 4 (PS4)) is very distinct morphologically from the other Indian species of the genus. Siriwut et al. (2015) noted that it is the most anomalous member of Digitipes morphologically and comparison can be made with species of Otostigmus in its robust, dorsally grooved ultimate legs. They added that the complete or nearly complete paramedian sutures on sternites in D. periyarensis should be emphasised because they resemble a condition found in other genera of Otostigminae (some species of Otostigmus ) and that the membership of this species within Digitipes is heavily reliant on its molecular placement.

Siriwut et al. tabulated the taxonomic characters of the eleven species of the genus including their new species Digitipes kalewaensis Siriwut, Edgecombe & Panha, 2015 from Myanmar. The aggregated data for six Indian species are given in Table 4 together with D. kalewaensis , D. periyarensi s (the seventh Indian species) and O. nudus .

In addition to the almost complete sternite paramedian sutures and dorsally grooved ultimate legs Digitipes periyarensis differs from the other Indian species by the coxosternal tooth-plates being longer than wide rather than wider than long, the coxopleural pore-field not being widened anteriorly, the complete absence of tarsal, tibial and femoral spurs as opposed to femoral and tibial spurs on leg 1, two tarsal spurs on anterior legs and a single tarsal spur to leg 19 or 20 (no precise data on the distribution of tarsal spurs in D. chhotanii ). The ultimate legs of the two specimens of D. periyarensis do not show the longitudinal groove along the medial surface of the femur or the conical to subcyclindrical distomedial femoral process present in the males of other Digitipes species and for this reason Joshi and Edgecombe regarded them as females.

Digitipes periyarensis is morphologically identical in almost all respects to O. nudus (see Table 4 ). The principle differences between them are the presence of a weak median keel on the tergites in O. nudus and in the greater development of the grooves and the presence of pits on the prefemur, femur and tibia of the ultimate legs of D. periyarensis . As shown above for O. geophilinus the degree of development of the grooves can vary considerably. These differences may be sexual or due to individual variation but do not seem sufficient to regard the two as separate species.

It is here proposed that D. periyarensis is a junior subjective synonym of O. nudus . The alternative would be to transfer the other morphologically similar Otostigmus species namely, the O. nudus , O. sulcipes , O. sutteri , O. geophilinus and possibly O. taeniatus and O. cuneiventris to Digitipes although no specimens show the distomedial process on the femur of the ultimate leg characteristic of mature male Digitipes and it seems very unlikely that all are females.

Figures

FIGURES 9–16. Foetus stadium Otostigmus sulcipes Malacca. 9. Distal four articles showing article 16 subdivided into two beneath the foetal cuticle spm 1. 10. Cephalic plate spm. 1. 11. Detail of cephalic plate showing possible ocelli spm. 2. 12. Pretarsus of second maxillary telopodite spm.1. 13. Forcipular coxosternal tooth-plates spm. 1. 14. Coxopleuron and sternite of ultimate leg-bearing segment spm. 1, ventral view. 15. Ultimate leg prefemur spm. 2. 16. Detail of ultimate leg prefemur showing developing spines. FIGURES 17–22. Otostigmus trisulcatus 17. Forcipular coxopleural tooth-plates syntype 13365. 18. Left forcipular trochanteroprefemoral process, the same. 19. Sternite 14, the same. 20. Coxopleuron and sternite of ultimate leg-bearing segment and ultimate leg prefemoral, the same, ventral view (coxal pores not shown). 21. Right coxopleuron syntype ZMB 13365, slide 4002. 22. Ultimate leg prefemur syntype 13365, dorsal view. Scale bars = 0.5 mm except Fig. 12, 13 & 16 = 0.1 mm.

FIGURES 51 – 59. Otostigmus cuneiventris. 51. Forcipular coxopleural tooth-plates, syntype spm. 2, Mapanja. 52. Sternite 12 syntype spm. 1. 53. Sternite of the ultimate leg-bearing segment syntype spm. 2. 54. Loose ultimate leg prefemur of a syntype ventral view. 55. Head and tergites 1 & 2, Bonge spm. 56. Sternite 12 Bonge spm. 57. Coxopleuron and sternite of ultimate legbearing segment and right ultimate leg prefemur Bonge spm. 58. Detail of right coxopleural process, ventral view. 59. Forcipular coxopleural tooth-plates Kilimanjaro spm. 1.

Tables

TABLE 3. Comparison of morphological characters of Otostigmus cuneiventris and the African species of Digitipes. Significant differentiating characters in bold.

	O. cuneiventris	D. krausi	D. reichardti	D. verdascens
	Cameroon, Tanzania	D. R. Congo	Tanzania, D.R. Congo	D. R. Congo
Maximum length (mm)	56	58	31	32
Antennal articles	17	17	16 (17)	17
Basal articles glabrous	3	3	3	3
Forcipular coxosternal tooth- plates	Longer than wide	No data	As wide as long	No data
Teeth on coxosternal tooth- plates	4+4	4+4	4+4	4+4
Complete tergite paramedian sutures from	6	5	6	6
Tergites marginate from	8	21 only	21 only	21 only
Sternite paramedian sutures/sulci	None	None	Complete or almost on some sternites	Complete
Sternite longitudinal depressions	3 or 5	3	One median (weak)	No data
Sternite posterior round depressions	3 transverse	none	One median (weak)	No data
Coxopleural process spines	2 apical	2 apical	2 apical+1 lateral	2 apical
Coxopleural pore-field widened anteriorly	Very slightly	No data	Shape oval	No data
Legs with tarsal spurs	Some or None	None	1-2(3) with 2, 4-19 with 1	1-3 with 2, 4-19 with 1
Dorsomedial process on ultimate leg femur in males	Absent	No data	Present	Present
Ultimate leg dorsal grooves	Absent	Absent	Absent	Absent
Ultimate leg prefemoral spine rows	3	3	2	2
Number of spines	7(8)	7	5-6	3