Revolving SEM images visualising 3D taxonomic characters: application to six species of the millipede genus Ommatoiulus Latzel, 1884, with description of seven new species and an interactive key to the Tunisian members of the genus (Diplopoda, Julida, Julidae)

Abstract A novel illustration technique based on scanning electron microscopy is used for the first time to enhance taxonomic descriptions. The male genitalia (gonopods) of six species of millipedes are used for construction of interactive imaging models. Each model is a compilation of a number of SEM images taken consecutively while rotating the SEM stage 360°, which allows the structure in question to be seen from all angles of view in one plane. Seven new species of the genus Ommatoiulus collected in Tunisia are described: Ommatoiulus chambiensis, Ommatoiulus crassinigripes, Ommatoiulus kefi, Ommatoiulus khroumiriensis, Ommatoiulus xerophilus, Ommatoiulus xenos, and Ommatoiulus zaghouani spp. n. Size differences between syntopic adult males of Ommatoiulus chambiensis and Ommatoiulus xerophilus spp. n. from Châambi Mountain are illustrated using scatter diagrams. A similar diagram is used to illustrate size differences in Ommatoiulus crassinigripes, Ommatoiulus khroumiriensis spp. n. and Ommatoiulus punicus (Brölemann, 1894). In addition to morphological differences, the latter three species display allopatric distribution and different habitat preferences. A dichotomous interactive key with a high visual impact and an intuitive user interface is presented to serve identification of the 12 Ommatoiulus species so far known from Tunisia. Updates on the North African Ommatoiulus fauna in general are presented.

As useful as gonopod illustrations are for taxonomic descriptions, they can sometimes be grossly misleading and result in misidentification and production of synonymic names, the Achilles' heel of descriptive taxonomy. There are several examples of this in the literature about millipedes, but most striking is perhaps the case presented by Hauser (2000) who demonstrated that amongst 11 subspecies and 100 varieties described for Craspedosoma alemannicum Verhoeff, 1910(see Schubart 1963a, based on differences in the length of podosternite (posterior gonopods) processes, only 9% are valid while the rest can be discarded. The reason for this is that the 'heterodactyly' on which Verhoeff (1915Verhoeff ( , 1916Verhoeff ( , 1917Verhoeff ( , 1939 based his infraspecific Craspedosoma taxonomy and which was subsequently adopted by most authors studying the taxonomy and ecology of the genus, was simply due to observation error. When the podosternite of Craspedosoma is viewed from varying angles, the relative lengths of its processes change (see Hauser 2000, figs 1, 2, 3).
Useful taxonomic characters in Ommatoiulus are almost exclusively derived from the gonopods. Differences between species are often subtle, and the pronouncedly "3D" nature of the gonopods makes recognition of the differences difficult. In many older papers dealing with Ommatoiulus taxonomy, authors have dissected the different parts of the gonopods and have illustrated them separately which has led not only to "angle-of-view" problems, but also to difficulties of relating the various gonopod components spatially to each other. By applying the novel imaging technique we have overcome these problems.

The study group: Ommatoiulus millipedes from Tunisia
Ommatoiulus is the dominant genus of julid millipedes in North Africa and the Iberian Peninsula. A total of 70 species have been described so far, and many more remain to be recognised and named. For example, Akkari and Enghoff (2012) recorded 19 Ommatoiulus species in the southernmost Spanish region, Andalusia, 10 of which they described as new. These authors further provided a historical overview tracing the general inconclusive taxonomic situation and gave an updated definition of the genus based on morphological characters and a key to the 19 Andalusian species which they estimated to constitute at most 1/6 of the total species richness for the genus. In spite of the wide distribution of a few species, e.g. O. sabulosus (Linnaeus, 1758) reaching 64°N in Fennoscandia, and O. moreleti (Lucas, 1860) with a near-cosmopolitan, synanthropic distribution, most Ommatoiulus species are confined to the Mediterranean region of North Africa and Iberia, and tend even to display small-scale endemism. For instance, of the 19 species recorded from Andalusia, only five were found in other areas (Akkari and Enghoff 2012).
North African species of the genus were examined in considerable detail by several authors, especially Brolemann (1921Brolemann ( , 1924Brolemann ( , 1925a and Schubart (1952Schubart ( , 1960Schubart ( , 1963b. Recent studies have mostly targeted the Tunisian fauna, describing new species (Akkari andVoigtländer 2007, Akkari and and in some cases detailing some aspects of developmental modalities (Akkari and Enghoff 2011). Akkari et al. (2009) presented detailed species accounts and new records from Tunisia in addition to a complete bibliographical review of the order Julida in North Africa, listing 24 Ommatoiulus species for the region.
Despite these contributions, the North African Ommatoiulus fauna is far from being thoroughly assessed, nor is its taxonomy close to being fully revised. Without doubt, numerous new species still await discovery, and several taxonomic questions still remain unsolved, such as the correct placement of the highly deviating species O. lapidarius (Lucas, 1846), type species of the subgenus Apareiulus Brölemann, 1897 (e.g., Attems 1952, Schubart 1963b. The same applies to the O. punicus species group established to facilitate understanding species affinities (Akkari and Voigtländer 2007) but which, in the light of recent revisionary work on the genus (Akkari and Enghoff 2012), might not reflect true relationships. To solve these questions an exhaustive revision of the genus in this area is needed.

Material and methods
Most specimens were hand collected during spring 2008 by N.A. and P.S. Supplementary material was obtained from museum collections. All studied specimens are preserved in 70% alcohol. Measurements were made using a Leica Wild M10 microscope equipped with an ocular micrometre. Photographs were taken using Visionary Digital's BK Plus Lab with a Canon EOS 7D. For scanning electron microscopy, parts of the specimens were cleaned with ultrasound, transferred to 96% ethanol then to acetone, air-dried, mounted on adhesive electrical tape attached to aluminium stubs, coated with platinum/palladium and studied in a JEOL JSM-6335F scanning electron microscope. Photographs were processed with a Leica Application Suite program and final stacking made with Zerene Stacker 1.04. The rotatable images were constructed from 18 SEM images taken at 20 degrees intervals starting from the mesal view and continuing until all 360 degrees were captured by rotating the SEM stage. The images were processed using Adobe Lightroom 4.3 by adjusting the black, highlight and white levels to achieve a uni-form background and contrast. Each image was then cropped to ensure a smooth transition between each frame during rotation. The images were imported into Adobe Flash CS5, where each image was made into a single frame and the series combined to form a rotating animation. The animation controls (moving from one frame to the next) were mapped to the mouse cursor using Actionscript 3.0. The html version available online was compiled using Magic 360. The interactive key was developed in Adobe Flash CS5.5 using Actionscript 2.0 to handle screen transitions and image swapping. Plates were assembled using Adobe Indesign CS 5.5. Respective image libraries of the interactive rSEM have been deposited in MorphBank. More details on the method of creation of the interactive models can be found in Cheung et al. (2013). The number of body rings is given as recommended by Enghoff et al. (1993): Number of podous rings (PR) + number of apodous rings (AR) + telson (T). The developmental stadium of a number of individuals was taken as being represented by the number of vertical rows of ocelli (RO). The real stadium number in julid millipedes has been shown to equal the number of RO+1 (Enghoff et al. 1993), e.g., a specimen with 9RO belongs to developmental stadium 10.
Diagnosis. Most similar to O. xerophilus sp. n., but easily distinguished by the shape of promerite and the presence of a distal notch and a small pointed process on solenomerite.
Etymology. Named after the type locality. Châambi Mountain is the highest mountain range in Tunisia, reaching 1550 m at peak Châambi.
Description. Males: L: 17-23 mm, H: 1.6-2 mm, 46-49 PR+1-2 AR+T; females: L: 18.5-32.2 mm, H: 2.4-3.6 mm, 44-50 PR+1-2 AR+T. General colour brownish with a black sputter, dorsally darker, with a black mid-dorsal line. Head dark brown to black with yellow spots in the occipital area, uniformly black frontally, with yellow spots at antennal level and labrum, the latter yellow and brighter; antennae dark brown. Prozonites covered with yellowish-brown spots on a blackish background, also laterally, interrupted by big black spots at ozopore level, dorsally black with a narrow transverse row of yellow spots anteriorly; metazonites glossy pale to whitish; legs light brown to yellowish. Telson: anal valves black, with a yellow sputter, preanal ring black, somewhat paler on the caudal projection; subanal scale light brown. Prozonites with fine oblique striae; metazonites with regular striation, laterally narrower; suture complete, strongly curving at ozopore level; ozopores small, rounded, situated on metazonites, at about their diameter from the suture. Anal valves with numerous submarginal and marginal setae, ca. 2 setae on the surface; subanal scale rounded and setose; preanal ring protruding in a caudal projection with ca. 3+3 setae on the tip and a small hyaline process.
Male sexual characters. Mandibular stipites expanded in well-rounded posteriorventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite (P) bent anteriad (Figs 1, 2), proximally subrectangular, gradually narrowing in its distal third (Figs 1, 2); lateral margin with a moderately deep rounded incision (i). In a posterior view showing a distal process expanded in a subtriangular shape, bearing an apical blunt process (ap) and a lateral broad process pointing basad (lp); mesal ridge (M) apically broadened and delimiting a serrated lateral lamellar process; distal process laterally bearing a strong serrated ridge (se) marking a thickness on the posterior surface; telopodite (T) remnant ovoid located in the middle of the proximal part.
Posterior gonopod (Figs 3-6): Mesomerite (Ms) longer than the other processes of the gonopods, distally curved mesad and narrowing into an apical process folded and tapering toward the apex. Solenomerite (S) broad, slightly narrowing at midlength, proximally with several strong spikes (sp) on the posterior margin; anterior margin with a big, serrated process (pr) pointing distad, separated from the apical part by a rounded notch (n); apical part with an anterior marginally furrowed lamella (Figs 1, 4-6), and a setose wrinkled protruding lamella (wl) covering a protruding slender process (ds) (Figs 1, 3-6) housing the distal part and the opening of the seminal groove (g), the latter running from the fovea (F) at the base of the solenomerite up to process ds. Paracoxite (Px) broad and curved, emerging from a well-rounded coxite (Co), distal third broad then gradually narrowing in a rounded apex pointing mesad (Figs 3-6).
Distribution. Known only from the type locality, Châambi Mountain, Arid Bioclimatic zone, central Tunisia.
Habitat. Mixed forest with Quercus ilex and Pinus halepensis, under stones and in leaf litter.   To display the embedded multimedia object the use of Acrobat Reader (version 8 or higher) is required.
Diagnosis. Gonopods resembling those of O. punicus and O. khroumiriensis sp. n., but differing by the shape of promerite, a much broader and strongly serrated paracoxite, a broader mesomerite bearing subapical serrations on the mesal margin, and the apical processes on solenomerite.
Etymology. An adjunction of Latin words referring to the body size and leg colour, crassus meaning fat and nigripes, black leg.
Description. Males: L: 24.8-30 mm, H: 2.7-3.6 mm, 45-53 PR+1-2 AR+T. Females: 30-34 mm, H: 3.4-3.9 mm, 45-47 PR+1-2 AR+T. General colour grey, with alternating pale grey and golden brown, darker laterally, with a thin black mid-dorsal line. Head grey, with black sputter frontally, labral zone reddish-brown, brighter at the margin, antennae dark brown. Prozonites pale grey, with big black spots at the level of ozopores and below, a dense black sputter; metazonites whitish anteriorly and golden brown posteriorly, legs black. Telson: anal valves dark grey, bordered with black, preanal ring golden brown, darker on the tip of the caudal projection; subanal scale yellowish. Prozonites with scattered oblique striae; metazonites with regular striation becoming dense laterally; ozopores small and rounded, appearing as brown rounded spots located on metazonites, situated at about their diameter from the suture; the latter complete, only slightly curving at the level of ozopores. Anal valves mostly glabrous at the surface but bearing several submarginal and shorter marginal setae; subanal scale triangular, blunt and setose; preanal ring protruding in a caudal projection, with ca. 2+2 setae and a small hyaline process on the tip.
Male sexual characters. Mandibular stipites expanded in well-rounded posterior-ventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite ( Fig. 7) broad, proximally almost rectilinear, bent 90 degrees at notch level; strongly narrowing in its distal third with a deep incision (i) on the lateral margin, latter almost rectilinear; mesal ridge (M) broad distally, protruding in a blunt process (mp) (Fig. 7); posterior surface irregular on the mesal side, bearing a number of strong setae aligned in front of the notch; distal process (ap) laterally broadened and rounded, showing a small mesal serrated process (ap1); remnant of telopodite (T) as a small bump located proximally.
Posterior gonopod (Figs 8-13). Mesomerite (Ms) long, sinuous, distal part asymmetrically enlarged mesolaterally, and showing in lateral view strong serrations at different levels on both margins (Figs 8,9,13), gradually narrowed apically in a hookshaped process (ho) curved and tapering toward the apex (Figs 11,12,13). Solenomerite (S) broadest at the base, narrowing at mid-length and bearing a number of strong setae near the posterior margin (Figs 10, 12, 13); in mesal view showing at mid-length a triangular process (pr) pointing distad (Figs 10, 13), latter separated from the apical part by a deep rounded notch (n); apically bearing a long curved process (ds) pointing mesad, housing the distal part and the opening of the seminal groove (g) and emerging between a posterior and an anterior folded hyaline processes (hp1, hp2) . Seminal groove running from the fovea (F) at the base of the solenomerite up to process ds (Figs 10,13). Paracoxite (Px) lamellar, broad and folded, emerging from a rounded coxite (Co), distally broadened, apical margin almost Distribution. Semi-arid and Arid bioclimatic zones in west central Tunisia, recorded from the governorates Kasserine, El Kef, Thala and Kairouan.
Habitat. Dry and open habitats, to 1500 m in Châambi Mountain. Diagnosis. Differing from all congeners by having a tri-lobate distal part of promerite and a bifurcated apical part of mesomerite, the latter divided in two short oppositely directed processes.

Ommatoiulus kefi
Etymology. Named after El Kef city, the type locality of the species. To display the embedded multimedia object the use of Acrobat Reader (version 8 or higher) is required. Description. Male: L: 26 mm, H: 2.7 mm, 53 PR+1 AR+T. General colour alternating whitish and blackish with a thin black mid-dorsal line. Head brown, lighter on the frontal part, with yellowish spots at antennal level, labral zone yellowish, becoming brighter at the margin, antennae brownish. Prozonites pale grey, dorsally scarcely sputtered with black; metazonites anteriorly dark, with a blackish background and a line of light brown spots below ozopores; legs whitish. Telson: anal valves and preanal ring blackish, paler towards caudal projection, subanal scale yellowish. Prozonites with scattered oblique striae; metazonites with regular striation becoming dense laterally; suture complete and rectilinear; ozopores small, rounded and located in metazonites, well apart from the suture. Anal valves with numerous submarginal and marginal setae and ca. 1-2 setae on the surface; subanal scale triangular, blunt and setose; preanal ring protruding in a caudal projection, with ca. 3+3 setae and a small hyaline process on the tip.
Male sexual characters. Mandibular stipites expanded in rounded posterior-ventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite (Fig. 14) in posterior view subrectangular, mesal ridge (M) fairly broad, distally narrowing and protruding into a pointed apical lobe (al); apical margin protruding in a curved median lobe (me) pointing laterad and a shorter broad lateral lobe (lb); the three apical lobes separated by two rounded incisions; lateral margin almost rectilinear. Remnant of telopodite (T) ovoid, located at mid-length of promerite.
Posterior gonopod : Mesomerite (Ms) broadest at the base, distally protruding in a uniformly broad process, apically splitting into two short and curved To display the embedded multimedia object the use of Acrobat Reader (version 8 or higher) is required.
processes, pointing in opposite directions (m1, m2) (Fig 16, 17, 19); solenomerite (S) broad at the base, slightly narrowing at mid-length and showing a triangular process (pr) separated from the rest of the processes by a rounded (n) (Figs 17, 19), apical part of the solenomerite complex with a broad lamella (al1) extended latero-mesad, downturned and marginally furrowed (Fig. 16). Seminal groove (g) running from the fovea (F) at the base of solenomerite up to a slender and short conical process (ds) emerging on top of the median part of the apical lamella and pointing anteriad (Figs 15,17). Paracoxite (Px) stout, with smooth margins, emerging from a broad rounded coxite (Co) (Figs 18, 19). Distribution. Semi-arid bioclimatic zone in western Tunisia; hitherto known only from the type locality near El Kef city.
Comments. We have examined three females (MSNB) collected from the same locality but could not assign them with certainty to O. kefi as they show a different colour pattern. Diagnosis. Similar to O. punicus and O. crassinigripes sp. n. but readily distinguished by the shape of promerite having a deeper notch extended basad, much slen-derer processes of posterior gonopods, and a more sinuous mesomerite devoid of conspicuous serrations.

Ommatoiulus khroumiriensis
Etymology. The species name refers to the natural region of Khroumirie, NW Tunisia, to which the species seems confined.
Prozonites with scattered oblique striae; metazonites densely striated; suture complete, curving at ozopore level; ozopores small, rounded and located on metazonites, situated at about their diameter from the suture. Anal valves with 4-5 setae on the surface, a submarginal row of 12-13 setae and numerous short marginal ones; subanal scale triangular and setose; preanal ring protruding in a caudal projection with ca. 3+3 setae and a small hyaline process on the tip.
Male sexual characters. Mandibular stipites expanded in rounded posterior-ventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite (Fig. 20) strongly narrowed distally with a deep lateral incision (i) extending meso-basad, distal process (ap) broad, subtriangular, with two pointed edges, the tip of apical process with a small pointed lobe (ap2); mesal ridge (M) distally protruding in a blunt small cylindrical process (mp), posterior surface of promerite with a row of strong setae emerging at the level of the notch, in close proximity to the mesal ridge.
Posterior gonopod (Figs 21-26). Mesomerite (Ms) large, longer than the other processes, uniformly broad, sinuous; distal third constricted to less than half breadth and apically protruding into a slender curved process, latter tapering and pointing mesad (Figs 21,23,24,26). Solenomerite (S) broadest at the base, narrowing at midlength, and bearing a number of strong setae near the posterior margin, distally with a broad, blunt triangular process (pr) separated from the apical part by a rounded notch (n), and with a long curved process (ds) protruding between two apical hyaline processes (hp3, hp4) and housing the apical part of seminal groove (g), the latter (g) running from the fovea (F) located at the base of the solenomerite (S) up to process ds. Paracoxite (Px) emerging from a depressed coxite (Co); Px curved, half as broad as in O. crassinigripes, gradually narrowing distad; lateral and apical margins, with a saw-like strongly jagged margin (Figs 22-26).
Habitat. Mixed forests dominated by Quercus faginea and Q. suber, or Pinus pinaster and Quercus suber. Diagnosis. Resembling O. chambiensis and O. xerophilus spp. n. in size and general shape of gonopods, but distinguished by the shape of promerite, a much more slender mesomerite and shorter and stouter paracoxite.
Etymology. The species name is a Greek noun meaning 'stranger', emphasising the fact that this species, found surprisingly in the collection of the MNHN shortly before completion of the manuscript, had remained unknown and out of the sight of a number of myriapodologists for more than 150 years.
Description. Male: L: 20.5 mm, H: 1.85 mm, 47 PR+2 AR+T; females: L: 18.5-21 mm, H: 2.26-2.46 mm, 42-48 PR+2-3 AR+T. General colour faded, generally greygreenish (very likely an artefact from the decomposition of the inserted label), somewhat lighter laterally. Head pale in the occipital and labral areas; antennae and legs darker. Prozonites with darker triangular spots laterally, latter situated along the ozopores line and forming two longitudinal dark bands, dorsally separated by a pale one; dorsum crossed by dark triangular spots and showing a thin black mid-dorsal line; metazonites mostly pale and glossy. Telson: anal valves and preanal ring dark, subanal scale pale. Prozonites with fine striae; metazonites with regular striae, denser on the sides, suture complete, curving at the level of ozopores; ozopores small, rounded, situated on metazonites situated at about their diameter from the suture. Anal valves setose; preanal ring with 3-4 setae on each lateral side, protruding in a short caudal projection with 1-4/5 setae and a small hyaline process on the tip. Subanal scale blunt to rounded and setose.
Male sexual characters. Mandibular stipites expanded in rounded posterior-ventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite (Fig. 27) gradually narrowed distally, lateral margin with a shallow incision (i); apical process of promerite with a rounded margin pointing laterad; mesal ridge (M) narrow, distally protruding in a pointed apex (mp) separated from the apical process by a small apical incision; remnant of telopodite not very conspicuous.
Posterior gonopod (Figs 28-30): Mesomerite (Ms) uniformly broad proximally, strongly narrowed in its distal third and bent posteriad (Figs 28, 29); solenomerite (S) broad, with scattered setae on posterior margin, narrowing at mid-length, and bearing a large blunt process (pr); solenomerite apically with a broad folded lamella (Fl) and a small wrinkled lamella laying on the top of a slender and slightly protruding process (ds) housing the distal part of the seminal groove (g); seminal groove running from the fovea (F) and opening at the apex of process ds (Fig. 28). Paracoxite (Px) stout, distally curved mesad and narrowed into a slender apex pointing basad emerging from a broad and rounded coxite (Co) (Fig. 30).
Distribution. Exact locality unknown. The label mentions 'Tunis' which presumably refers to Tunisia in general.

Ommatoiulus xerophilus
Diagnosis. Resembling O. chambiensis in the structure of mesomerite, paracoxite, but well distinguished from the latter by the characteristic globular apex of promerite and the shape of solenomerite devoid of a rounded notch.
Etymology. The species name is a Greek adjective referring to the affinity of the species for dry habitats.
Prozonites with fine striae; metazonites with regular striae, becoming denser laterally, suture complete, curving at the level of ozopores; latter small, rounded, situated on metazonites situated at about their diameter from the suture. Anal valves setose, with 6-7 setae on the surface and numerous submarginal and marginal setae; subanal scale rounded and setose; preanal ring with 1+1 setae on the sides, protruding in a caudal projection with 3+3 setae and a small hyaline process on the tip.
Male sexual characters. Mandibular stipites expanded in rounded posterior-ventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite (P) (Figs 31, 32) bent anteriad, not very broad, with parallel margins, mesal ridge (M) broad, distally narrowing and truncate, bearing several serrations (se) and separated from the apical lobe (ap); by an incision; lateral margin mostly rectilinear, only slightly narrowing subapically at the level of the mesal incision; apical lobe globular, with rounded margin, curved laterad; posterior surface with a number of strong setae aligned distally; telopodite remnant inconspicuous.
Distribution. Arid bioclimatic zone, central Tunisia; hitherto known only from the type locality, Châambi Mountain.
Habitat. Open areas with scattered Pinus halepensis trees. Etymology. Named after Jebel Zaghouan, the type locality. Description. Male: L: 28.5 mm, H: 2.56 mm, 49 PR+1 AR+T. General colour alternate dark and light golden brown; dorsum with a thin black axial line. Head dark to blackish, with brownish spots on the frontal part and on the mandibular stipites, labral zone and mouth parts pale, marginally bright yellow; antennae brownish. Prozonites dark to blackish, covered with yellowish spots; metazonites pale brown to whitish laterally and golden brown dorsally, legs yellowish. Telson: anal valves black, preanal ring blackish, caudal projection yellowish, subanal scale yellowish. Prozonites with fine irregular striae; metazonites with regular striae, becoming dense laterally, suture complete, curving at the level of ozopores; ozopores small, rounded, situated in metazonites, situated at about their diameter from the suture. Anal valves setose, with 4-6 setae on the surface, ca 14 submarginal and numerous marginal setae; subanal scale rounded and setose; preanal ring with 2+2 setae on the sides, protruding in a caudal projection with (6-7)+(6-7) setae on the tip and bearing a small hyaline process.
Male sexual characters. Mandibular stipites expanded in rounded posterior-ventral lobes, first pair of legs hook-shaped, remaining legs with postfemoral and tibial pads.
Gonopods. Promerite (Fig. 36) proximally subrectangular, strongly narrowed distally by a deep incision (i) on the lateral margin; mesal ridge (M) broad, distally protruding in a serrated edge (se); apical part with a mesal triangular blunt process (rp) protruding mesodistad, and a lateral protruding process with two small apical bumps (bp1, bp2); posterior surface of promerite showing few scattered setae near the mesal margin; remnant of telopodite (T) large and ovoid, located at mid-length of the process.
Posterior gonopod (Figs 37-39): Mesomerite (Ms) large, and uniformly broad (Figs 37, 38) with a distal triangular pointed extension on the lateral margin (tp), distal third strongly curved mesoposteriad and narrowed in a long and slender apical process (Figs 37,38,39); solenomerite (S) broad, with scattered setae on posterior margin; anteriorly simply rounded devoid of processes; apically with a hyaline folded lamella (fl) and a slightly protruding process (ds) housing the distal part of the seminal groove (g); the latter running from the fovea (F) (Fig. 37) up to process ds. Paracoxite (Px) stout and curved apically slightly narrowing into a rounded apex directed mesad, coxite broad (Co) (Fig. 39).
Distribution. Semi-arid bioclimatic zone in northeastern Tunisia; known only from Zaghouan Mountain.
Habitat. Forest dominated by Pinus halepensis. Akkari et al. (2009) summarized all records of julidan millipedes, including Ommatoiulus species, from Tunisia and provided a complete list of the North African members of the order. A number of additions and corrections to the lists are presented here:

Updates to the list of Ommatoiulus species in North Africa
• We refute the presence of O. diplurus appendiculatus (Brolemann, 1925) in Algeria. This taxon is based on females and juveniles only, and Akkari and Enghoff (2012) already regarded the presence of O. diplurus (Attems, 1903) in North Africa uncertain. • The record of O. aumalensis (Brolemann, 1925) Manfredi 1939, Schubart 1952 with O. lapidarius, but re-examination of the holotype of J. rimosus (Museum für Naturkunde, Berlin) has shown that this is a valid species (Akkari 2013).

Discussion
Three of the new Tunisian Ommatoiulus species were found in Châambi Mountain, which is the highest mountain range in Tunisia. The mountain is located only a few kilometres from the Algerian border and in spite of its arid character is known to harbour a number of endemic species (cf. Kovařík 2006, Hartenberger 1986 (Fig. 40). Of special importance is the fact that the size difference is apparent within each developmental stadium. Thus, O. chambiensis males with 8RO have more podous rings and larger diameter than O. xerophilus males with 8RO. The same is true for specimens with 9RO although the studied material is much smaller. O. crassinigripes is the only schizophylline millipede collected at more than 1500 m elevation in Tunisia. However, it occurs also at lower elevation in central Tunisia (El Kef, Thala, Makthar, Kairouan) and is very unlikely to be an alticolous species like Ommatoiulus gravieri (Brolemann, 1924), which is known from 3000-3200 m altitude in Jebel Tachdirt of the High Atlas in Morrocco (Brolemann 1924, Akkari et al. 2009. O. crassinigripes is one of the largest Ommatoiulus species in Tunisia and, together with O. khroumiriensis, is the closest to O. punicus with regard to gonopod shape (Fig. 41). The three species, which were all treated under O. punicus by Akkari et al. (2009), have quite similar gonopod conformations, yet display a number of constant differences in both promerite and posterior gonopods (Table 1). Although resembling, differences in posterior gonopods can be clearly noticeable on the rotatable models (Figs 13,26,41), which, in addition to the external morphological features, indicate their separate taxonomic status. The external morphological differences concern colour pattern and size.  is mainly distributed around Tunis City, Cap Bon Peninsula and the eastern part of the Ridge viz. Zaghouan Mt. in the north (see Akkari et al. 2009). O. punicus was recorded from Aïn Draham, Tabarka and Nefza, as well as from Kairouan Plain by Akkari et al. (2009). These authors pointed out the variation observed in the material: "Ommatoiulus punicus as currently delimited is quite a variable taxon, and a detailed analysis may well necessitate splitting it into several (sub)species." Our renewed study has corroborated this assumption. Attems (1903Attems ( , 1926 (Attems 1926, figs 240-241) is O. khroumiriensis. On the other hand, the record of O. punicus from unspecified locality in Tunisia (Attems 1903: 144, figs 77-81) is here referred to as O. crassinigripes. Intercalary males are here recorded for the species Ommatoiulus khroumiriensis and O. crassinigripes. This is of little surprise considering that postembryonic development involving periodomorphosis (regression of secondary sexual characters followed by a return to a morphologically copulatory stadium following an additional moult) is considered as particularly prevalent for schizophylline species (Enghoff et al. 1993). Characteristic morphology of intercalary stadia was directly observed on reared specimens of three schizophyllines: O. moreleti (Lucas, 1860), O. sabulosus (Linnaeus, 1758) and Tachypodoiulus niger (Leach, 1814) while field-collected samples provided periodomorphic specimens belonging to no less than 8 species of genus Ommatoiulus, including O. punicus (see Akkari and Enghoff 2011 for species list). The same authors discussed the particular case of the species O. sempervirilis for which a large hand-collected sample revealed the complete absence of intercalary stadia and presence instead of four successive stadia of adult males implying a direct copulatory-copulatory succession (Akkari and Enghoff 2011).
Colour pattern and somatic characters cannot be used reliably to distinguish the Tunisian Ommatoiulus species, although we have provided information about these features above in order to point out fine differences between morphologically close or syntopic taxa. In the identification key (below) we prefer to include only gonopod characters. To display the embedded multimedia object the use of Acrobat Reader (version 8 or higher) is required.

Identification key to Tunisian Ommatoiulus species
The key is based on characters of the male gonopods.

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Apical process of promerite (ap) bulgy, with a lobed process (ap1) on tip (Fig.  7); mesomerite (Ms) with strong subapical mesal serrations (Fig. 8); paracoxite (Px) broadened distally with truncated apex (Fig. 12) ........... O. crassinigripes -Apical process of promerite slender, without a lobed process; mesomerite (Ms) without mesal serrations (Fig. 52); paracoxite (Px) distally narrowed, with rounded apex (Fig. 53)  Interactive key to Tunisian Ommatoiulus species We provide an interactive key in Flash (SWF) format to the Ommatoiulus species known from Tunisia. The key is dichotomous and based on gonopod characters. These are illustrated with line drawings, light microscopy photographs and SEMs, and for some of the species with rotatable SEM animations. A species list and species pages are included in the key to provide additional information on species diagnostic characters, distribution and habitats. An introductory section for the first-time user provides background information of importance for applying the key. Adobe Flash Player (version 11.2 or higher) or a browser (e.g. Internet Explorer, Firefox and Chrome) with Flash Player plug-in is required to run the key.
To display the embedded multimedia object the use of Acrobat Reader (version 8 or higher) is required.