Stygiiulus insularis ( Strasser, 1938 ) Vagalinski & Borissov & Bobeva & Canciani & Antić, 2022

Vagalinski, Boyan, Borissov, Simeon, Bobeva, Aneliya, Canciani, Giacomo & Antić, Dragan Ž., 2022, The mostly cavernicolous millipede genus Stygiiulus Verhoeff, 1929, stat. nov.: taxonomy, distribution and phylogenetic relationships (Diplopoda, Julida, Julidae), European Journal of Taxonomy 798, pp. 30-69 : 47-48

Stygiiulus insularis ( Strasser, 1938) comb. nov.

Figs 10C , 11C , 13

Typhloiulus insularis Strasser, 1938: 399–402 , fig. 10.

Typhloiulus insularis – Vagalinski et al. 2015: 340 . — Antić et al. 2018: 263–264 ; figs 5–6, 18c.

Material examined

CROATIA • 1 topotype ♂; Island of Cres , Beli , Petričevići, Čampari Pit; 8 Apr. 2001; R. Ozimec and B. Jalžić leg.; IZB • 1 topotype ♀; same collection data as for preceding; 20 Oct. 2000; CBSS .

Diagnosis

A species of Stygiiulus stat. nov. with normal mouthparts. Distinguishable from congeners by its smaller body (L = 10–16 mm) and shorter legs in relation to H, by the ozopores being placed on or right behind the pro-metazonal suture instead of at considerable distance behind it, and in several aspects of gonopod structures ( Fig.10C ), viz., ridge- rather than knob-like internal lobe of the promere, spoon-shaped mesomere, rather robust opisthomere without a posterior hump (the latter shared with S. seewaldii comb. nov.), long basal spine at flagellum channel (sometimes present in S. rotundatus comb. et stat. nov. and S. fimbriatus comb. et stat. nov.), and the presence of a distinct distal outgrowth (do) on velum (seen also in S. seewaldi comb. nov. and S. tobias comb. nov.).

Descriptive notes

ANTENNAE. 1.6 times as long as head and 1.65 as long as H in the male, and 1.35 and 1.3 times, respectively, in the female; antennomere 5 ca 1.6 as long as broad; antennomeres 2 and 5 subequal in length, ca 1.3 times as long as 3 and 4, and 1.5 times as long as 6.

TARSUS OF MID- BODY LEGS. Ca 2.7 times as long as tibia and ca 3.7 times as long as apical claw. Mid-body legs 1.25 times as long as H in the the male and 0.7 times in the female.

FEMALE SEXUAL CHARACTERS. Leg-pairs 1 and 2 visibly longer and thicker than following legs. Vulva ( Fig. 11C ) of nearly equal width in both the sagittal and the transverse planes, mostly symmetric; bursa with a narrow median cleft; each valve distally with a vertical row of 2–4 setae; operculum (op) proximally broad, distally abruptly narrowing, ending with a more or less straight apical margin, exceeding bursa by ca 1 ⁄ 8 of total height of vulva, disto-laterally with one vertical row of setae each side. Receptaculum seminis consisting of a very short and narrow, somewhat bent, median tube (mt) leading to a minute piriform ampulla (ma), and a slightly longer, mostly straight, lateral tube (lt) ending in a minute spherical ampulla (la).

Distribution

Known only from its type locality, the Čampari Pit on the island of Cres in Croatia ( Fig. 13 , red square).

Remarks

Strasser’s (1938) description of S. insularis comb. nov. was based upon four females only. Due to the absence of male specimens, this species has remained enigmatic for 80 years, until Antić et al. (2018) described the

first male and, according to the gonopod structure, hypothesized this species could belong to Stygiiulus stat. nov. Here we follow that assumption, which is further supported by the vulval structure, and formally transfer insularis to the genus Stygiiulus stat. nov. However, this species is obviously different externally compared to other Stygiiulus stat. nov. members, and is characterized by a smaller body and proportionatelly shorter antennae, as well as by a more anterior position of the ozopores.And while these external differences (or some of them) may be connected with its currently unknown ecology rather than with its phylogenetic affinities, certain gonopod characters, viz., the aforementioned spoon-like shape of the mesomere and the robustness of the opisthomere, plus a ridge- rather than knob-like internal lobe of the promere leave some doubts about the exact systematic position of insularis . But since the general gonopod conformation in this species is much more similar to other Stygiiulus stat. nov. than to any other typhloiulinine/blind leptoiulinine genus, we have opted here to formally place this interesting taxon in the aforementioned genus. Nevertheless, we are aware that in the future this tiny species could find its place in another (new) genus.

The Čampari Pit is also the type locality of another julid species, the pachyiulinine Chersoiulus ciliatus Strasser, 1938 . Both S. insularis comb. nov. and C. ciliatus are strict endemics of this pit and are listed as critically endangered species (CR) in the Red Book of the Croatian cave dwelling fauna ( Ozimec et al. 2009).

Figures

Fig. 10. Left gonopods of species of Stygiiulus stat. nov., mesal views. A. S. ausugi (Manfredi, 1953) comb.nov.,topotype♂(NHMD).B.S.illyricus(Verhoeff,1929)comb.nov.,redrawnfromVerhoeff (1929). C. S. insularis (Strasser, 1938) comb. nov., redrawn from Antić et al. (2018). D. S. maximus (Verhoeff, 1929) comb. nov., redrawn from Verhoeff (1930). E. S. seewaldi (Strasser, 1967) comb. nov., redrawn and modified from Strasser (1967). F. S. tobias (Berlese, 1886) comb. nov., ♂ from Grotta [Cave] del Subiolo (NHMD). Abbreviations: do = distal outgrowth of velum. Drawn not to scale.

Fig. 11. Left vulvae of species of Stygiiulus stat. nov. (A–D) and representatives of (other) Julini/ Leptoiulini (E) and Typhloiulini/blind Julini/Leptoiulini in caudal, somewhat mesal views. A. S. ausugi (Manfredi, 1953) comb. nov., ♀ from Grotta [Cave] del Calgeron (NHMD). B. S. illyricus (Verhoef, 1929) comb. nov., ♀ from Rabakova Cave (IZB). C. S. insularis (Strasser, 1938) comb. nov., topotype ♀ (CBSS). D. S. tobias (Berlese, 1886) comb. nov., ♀ from Grotta [Cave] del Subiolo (NHMD). E. Leptoiulus cf. trilineatus(C.L. Koch, 1847), ♀ from Belasitsa Mtn, Bulgaria. F. Serboiulus spelaeophilus Gulička, 1967, ♀ from Vodni Pech Cave (NMNHS). G. Typhloiulus (Inversotyphlus) lobifer Attems, 1951, ♀ from Minjera-Bauxite Mine (IBER). H. Typhloiulus (s. str.) strictus (Latzel, 1882), ♀ from Kunino (IBER). Abbreviations: at = anterior tube; la = lateral ampulla; lt = lateral tube; ma = median ampulla; mt = median tube; op = operculum; pa = posterior ampulla; pt = posterior tube. Scale bar = 0.2 mm.

Fig. 13. General distribution of the species of the genus Stygiiulus stat. nov.