Svaniulus ryvkini Vagalinski, gen. nov., 2021

Vagalinski, Boyan & Golovatch, Sergei I., 2021, The millipede tribe Brachyiulini in the Caucasus (Diplopoda, Julida, Julidae), ZooKeys 1058, pp. 1-127 : 1

Svaniulus ryvkini Vagalinski, gen. nov. sp. nov.

Figs 47 , 48 , 49

Material examined

(ZMUM): Holotype: ♂ (in head and 5 pieces, left antenna, penis, leg pairs 1 and 2, penis, gonopods, right flange of pleurotergum 7, mid-body leg, and hypoproct dissected), Georgia, Svanetia , mouth of Nenskra River, Lukhi, N of Khaishi, ca. 800 m a.s.l., leaf litter, 2.IX.1986, A. Ryvkin leg. Paratype: 1 ♀ (in 2 pieces, left vulva dissected), 5 juv. (unbroken), same collecting data as for holotype .

Diagnosis.

Differs from its only known congener, S. waltheri gen. nov., sp. nov., mainly by being on average slightly smaller, by the relatively shorter male antennae, by the position and shape of the ventral protrusions of male body pleurotergum 7, and by the following details of gonopod structure: promere proportionally broader, abruptly narrowing only apically, with the mesal process significantly exceeding the apex, vs. the same being more slender, gradually narrowing distally, and with the mesal process just slightly exceeding the apex in S. waltheri gen. nov., sp. nov.; opisthomere possessing a distomesal process vs. this being absent from S. waltheri gen. nov., sp. nov., having a broad and flat apical margin of the basoposterior process, vs. the same forming a distinct apical corner in S. waltheri sp. nov., and with the solenomere gradually narrowing all the way to the top, vs. the same being somewhat enlarged apically in S. waltheri gen. nov., sp. nov.

Name.

Honours Aleksandr B. Ryvkin, a coleopterist and the collector of the specimens used for the description of this new species.

Description.

Measurements: holotype in S IX, 42+1+T, L = 23 mm, H = 1.6 mm; paratype ♀ in S X, 46+1+T, L = 27 mm, H = 2.2 mm.

Colouration (> 30 years in alcohol) (Fig. 47 ): Head and collum with the usual colour pattern, antennae dark brown; trunk dorsally mostly brown-grey, with a blackish axial line and with dark grey to blackish transverse stripes running along pro-metazonal suture on both pro- and metazonae, reaching down to ozopore level; contrasting lighter brown-beige below ozopore level; frontal sections of prozonae brown-beige, posteriorly with an irregular dark brown spot around ozopore; metazonae mostly lighter than prozonae, their posterior sections with a dark brown band encircling entire ring, these narrowing and lightening ventrally; hind margins ochre-brown; epiproct dorsally dark grey, laterally dark brown; hypoproct and proximal part of paraprocts mostly light brown; legs yellowish.

External structures: Eye patches consisting of 27 or 28 and 37 or 38 markedly convex ommatidia, in the male and female, respectively; developmental rows easily countable. Vertigial, supralabral, and labral setae: two, four, and 20, respectively. Antennae ca. 1.35 × as long as head in the male, and 1.25 × in the female; antennomere 2> 3 ≥ 5 ≥ 4> 6. Gnathochilarium with a moderately sized promentum separating lamellae linguales by nearly half their length, each latter with four setae in a longitudinal row; male stipites basolaterally each with a faint oblong hump bearing several setae. Collum mostly smooth, with only several sparsely set, short and shallow grooves near posterolateral corners; frontolateral margin gently concave.

Body rings considerably vaulted. Prozonae with densely set, very short, shallow, parallel, longitudinal striae in their hind sections. Metazonae moderately deeply striated, n Schub = 9 or 10 in the male, and 10 or 11 in the female; setae erect to somewhat slanting, from ca. 2/5 (in mid-body and caudal rings) to equal to metazonal length (in anteriormost rings). Ozopores set tightly behind pro-metazonal suture in more anterior rings, and ca. half their diameter behind in more posterior ones; sutures gently to considerably sinuous in front of ozopores in most rings. Tarsus of mid-body legs equal to tibia, and slightly> 3 × as long as apical claw.

Telson (Fig. 47B ): Epiproct rather long (slightly exceeding the level of longest paraproctal setae in the male, just reaching it in the female) and straight, ending up with a well-developed, blunt, unciform, hyaline tip bent dorsad; with several long setae on dorsal side. Hypoproct in the male (Fig. 48A ) rounded trapezoidal, with a thickened, faintly undulate, caudal margin slightly protruding behind caudal contour of paraprocts, this being broadly rounded, thinner, and tightly adhering under paraprocts in the female; with a pair of long distal paramedian setae. Paraprocts rather sparsely covered with long setae, without rows of shorter setae at caudal margins.

Male sexual characters: Mandibular stipites (Fig. 47A ) considerably expanded, protruding ventro-anteriad, forming a subrectangular, rounded, ventro-anterior corner. Leg pair 1 compact parallel hooks. Leg pair 2 slightly shorter and thicker than following legs, both tibial and postfemoral adhesive pads well-developed, crested in anterior part of body, gradually reduced in the last third, completely absent from caudalmost legs; femora without modifications. Pleurotergum 7 ventrally forming blunt and spade-shaped lobes (Fig. 48B ) originating entirely from metazona, oriented with their broad sides parallel to the body axis, protruding mostly mesad, touching one another behind gonopods. Penis (Fig. 48C ) very small, deeply hidden above coxae 2, barrel-shaped, slightly longer than broad, strongly flattened dorso-ventrally, with very short apical lobes ending in short and blunt terminal lamellae directed distad.

Gonopods (Fig. 49 ): Promere (Fig. 49B, C and p in Fig. 49A ) relatively slender, somewhat higher than opisthomere, leaf-shaped, with a gently convex mesal margin, and a markedly sigmoid lateral one, both joining in a narrowly rounded apex; caudal surface with a massive and long mesal process originating at mid-height, ending with a short unciform apex turned baso-anteriad, considerably exceeding the apex of main promeral body; a short, well-pronounced, median ridge, a broad and weakly defined median groove, and a short and well-pronounced distal ridge just lateral to base of mesal process; flagellum just slightly shorter than height of promere. Opisthomere (Fig. 49A, D-F ) slender; basoposterior process present as a broad, anterocaudally flattened lobe ending with a flat apical margin bent caudad and bearing short and micro-papillary branches, mesally expanding into a short lobe with a coarse margin; mesomeroidal lobe a weakly pronounced ridge; a thumb-like distomesal process originating from border between basoposterior process and solenomere, directed distomesad; anteromesally at base a well-developed, elongate lobe (presumably gonocoxal gland); solenomere unipartite, long, flattened on sides, gradually narrowing distad, gently sigmoid, caudo-apically with a very fine and sharply pointed process; a dense row of small, erect, spiniform filaments at flagellum channel’s mid-height.

Female sexual characters: Leg pairs 1 and 2 somewhat shorter, 1st also slightly thicker, than following legs. Vulva (Fig. 48D ) slightly asymmetrical (lateral valve of bursa more strongly slanting towards apex compared to mesal one), rather elongate, subconical, strongly compressed on sides; bursa with a distinct, obtuse, postero-apical margin; an opening absent, with the two valves completely fused all the way to bursal apex; operculum slightly shorter than bursa, both structures ending up with ear-like hyaline protrusions, bursal ones considerably larger; setation dense throughout. Receptaculum seminis composed of a short and very narrow central tube abruptly widening into an oblong central ampulla, forming several constrictions followed by a digitiform reservoir at bottom; and a long and thin, slightly folded, posterior tube, this somewhat widening before ending in a subspherical posterior ampulla.

General distribution.

SWGC.

Remarks.

In the absence of a bursal opening and considering the position of the central tube of the vulval receptaculum, which is displaced strongly anteriad, at the border with the operculum, the only way for the male opisthomere to reach the receptaculum would be through widening the gap between the bursa and operculum, with the slender, gradually attenuating solenomere ending with a short and sharply pointed process that seems to serve as a perfect tool for that purpose. This is an obvious and rare example of co-evolution of gonopods and vulvae within Julidae , the family being generally characterised by highly specialised posterior gonopods with species-specific apical parts, in contrast to the more simply and uniformly built vulvae which are often barely distinguishable even between different genera of the same tribe.

Figures

Figure 47. Svaniulus ryvkini gen. nov., sp. nov., ♂ holotype A head and body rings 1 - 4 B telson, lateral views. Not to scale.

Figure 48. Svaniulus ryvkini gen. nov., sp. nov., ♂ holotype (A-C) and ♀ paratype (D) A hypoproct, ventral view B right flange of pleurotergum 7, ventro-lateral view C penis, caudal view D left vulva, mesal view (setae omitted). Scale bars: 0.1 mm. Abbreviations: ca. central ampulla, ct central tube, pa posterior ampulla, pt posterior tube.

Figure 49. Svaniulus ryvkini gen. nov., sp. nov., gonopods of ♂ holotype A left gonopods, mesal view B distal part of right promere, lateral view C right promere, caudal view D right opisthomere, meso-caudal view E same, oral view F distal part of the same, meso-caudal view. Scale bars: 0.1 mm (A-E), 0.05 mm (F). Abbreviations: bpp basoposterior process, dmp distomesal process, dr distal ridge, f flagellum, fc flagellum channel, g (supposed) gonocoxal gland, ml mesomeroidal lobe, mp mesal process, mr median ridge, msl mesal lobe of basoposterior process, p promere, pt posterior tube, s solenomere, sf spiniform filaments, sp apical process of solenomere.