A new genus of mongoliulid millipedes from the Far East of Russia, with a list of species in the family (Diplopoda, Julida, Mongoliulidae)

The genus Koiulus gen. nov. and its type-species, Koiulus interruptus gen. et sp. nov., are described from the Russian Far East. The new genus is compared with other genera of Mongoliulidae, in particular with Ussuriiulus Golovatch, 1980, also from the Russian Far East, with which it shares the absence of ozopores from individual body rings distributed along the body, a condition so far otherwise unknown in the superorder Juliformia. A synoptic table of genera and a list of species of Mongoliulidae are presented.


Material and methods
The material treated here has been deposited in the collections of the Zoological Museum, University of Copenhagen, Denmark (ZMUC), Federal Scientific Center of the East Asia Terrestrial Biodiversity, Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia (FSCB) and the Zoological Museum of the State University of Moscow, Russia (ZMUM).Paratypes of Uenoiulus notabilis Murakami, 1971 were borrowed from the National Museum of Nature and Science, Ibaraki, Japan (NMNS).The material was preserved in 70-75% alcohol and examined in alcohol under a stereo microscope.Gonopods and some other parts were dissected from a limited number of males and females and mounted in Canada balsam or temporarily in glycerine.
The numbers of podous and apodous rings were counted, and body length and midbody vertical diameter were measured on all entire specimens.For females, only maximum values are given because of difficulties in distinguishing juvenile and adult females without dissection.
Specimens for scanning electron microscopy (SEM) were transferred to 96% ethanol, then to acetone, air-dried, mounted on aluminium stubs or on pieces of flexible aluminium tape and in turn mounted on stubs, coated with platinum-palladium and studied in a JEOL JSM-6335F scanning electron microscope.SEM images were processed in PhotoShop and plates were composed in Microsoft Publisher.

Diagnosis
A genus of Mongoliulidae characterized by lacking ozopores on certain body rings (shared with Ussuriiulus), strongly reduced, three-segmented second male legs, strongly reduced seventh male legs (shared with all other genera except Ussuriiulus), strongly reduced flagella of anterior gonopods, posterior gonopods deeply split into two equally long processes: a slender anterior and a broad posterior one.

Etymology
The specific epithet refers to the River Ko where the type locality is situated.

Etymology
The species is named after the interrupted series of ozopores.Colour (Fig. 1).Marbled brownish, darker dorsally, no pronounced colour pattern.Defense glands visible as dark spots on the body rings on which they occur (see below).Male from environs of Zolotoi village beige (probably faded by preservation).Eye patches black.Antennae brown.eye patChes.Subtriangular, composed of 30-45 ocelli.A pair of long frontal (epicranial) setae (broken in many specimens), at least some individuals with scattered additional long setae between antennal sockets and labrum.2+2 supralabral setae, at least 5+5 labral setae.
Mandibles (Fig. 3A-C).External tooth (odontomere of Hoffman & Howell 1995), with three cusps decreasing in size from posterior to anterior.Internal tooth (dentate lamella of Hoffman & Howell 1983, sectile edge of psectromere of Hoffman & Howell 1996), with ca 5 cusps decreasing in size from posterior to anterior.Eight rows of simple pectinate teeth.Molar plate without grooves, with a row of hand-like processes, each with 3-5 bent 'fingers', along anterior margin.
GnathoChilariuM (Fig. 3D-E).Three apical setae on each stipes and four or five setae in a longitudinal row on each lamella lingualis; promentum (modified in male, see below) completely separating lamellae linguales.

ENGHOFF H. et al., A new genus of mongoliulid millipedes from the Far East of Russia
ColluM (Fig. 4B).Smooth, with one or two striae along lower margin.
body rinGs (Figs 1,.Slightly vaulted, prozonites smooth, metazonites with longitudinal striae in ventral half.A row of short setae on posterior margin, length of setae ca 0.1 × body diameter.Ozopores present from ring 6 onward, but missing from rings 7, 11, 14 or 15, one of rings 17-20 and several single rings further backward (Fig. 4C).Figs 1, 4a).Preanal ring with a short dorsal process and setae along posterior margin.Anal valves each with two setae.Subanal scale with two setae.4a-C).Moderately long and slender.Claws long, weakly curved, without modifications.

First pair oF leGs (Figs
seCond pair oF leGs (Fig. 5D-F).Strongly reduced, consisting of an unpaired (coxo?)sternum and threesegmented telopodites.Telopodomere 1 cylindrical, gently curved, ca 3 times as long as broad, with scaly microsculpture on posterior surface and a long disto-mesal seta on anterior surface.Telopodomere 2 barrel-shaped, slightly longer than broad, with a long disto-mesal seta on anterior surface and several shorter, scattered setae.Telopodomere 3 contrastingly black, tapering to narrow tip, here with a bunch of ca 7-8 stout setae with irregularly multi-spiked tips (Fig. 5F); several normal setae scattered over telopodomere surface.penis (Fig. 5D-E).Unpaired, cylindrical, longer than second legs, gradually narrowing towards end or with a slender, parallel-sided tip.
seventh pair oF leGs 6).Strongly reduced, each leg consisting of three-four podomeres of uncertain homology.Podomere 1 almost twice as long as podomere 2; podomere 1, sometimes also podomeres 2 and 3, with scaly microsculpture on mesal surface and a long (disto-)mesal seta, podomere 2 further with a few short setae.Podomere 3 contrastingly black, pear-shaped or conical, smooth or with a few short setae, sometimes surmounted by a tiny podomere 4 carrying 5 strong setae laterally and a claw apically (Fig. 6).

European Journal of Taxonomy
posterior Gonopods (Fig. 8).Each posterior gonopod divided from the basis into two equally long branches.Anterior branch (AB) slender, almost parallel-sided, mesally excavated, apical ⅓ with dense cover of retrorse mico-spicules; tip slender, curved up in densely microspiculate spiral.Posterior branch (PB) broad at base, tapering regularly towards tip and hence with a triangular outline; anterior surface excavated for accommodation of anterior branch; an anterior-lateral row of ca 15 short setae; mesal margin distally with subtriangular, anteriad lobes.

Female sexual characters
vulva (Fig. 9).Placed vertically in short vulval sacs behind unmodified second leg-pair, very slender, oblong pyriform.Operculum (OP) slightly longer than bursa, with two parallel rows of short setae on anterior surface and several strong setae on distal half; tip subtriangular.Bursa (BU) consisting of a single sclerite, but with longitudinal sutures in basal ¾ of mesal and lateral sides; four longitudinal rows of setae, one on each side of the two longitudinal sutures.Posterior surface apically divided into two rounded lobes.
A tiny (~15 µm) structure of unknown identity was observed next to one of the apical bursal setae (Fig. 9D (arrow)-E).It is sausage-shaped, has an apical pore and is apparent attached by its basal end to the surface of the bursa as well as laterally attached to the neighbouring seta.

Comparison of Koiulus gen. nov. with other Mongoliulidae
The Mongoliulidae is a small family of julidan millipedes, geographically confined to East Asia (Russian Far East, Korea, China, Japan).The family is closely related to the mainly North American family Parajulidae; the sister-group relationship between the two families is supported by morphological characters (enlarged first male legs, enlarged and soft male promentum; Enghoff 1981) and Kopidoiulus continentalis (Mongoliulidae) comes out as sister group to Uroblaniulus caroliniensis Causey, 1953 (Parajulidae) in the molecular phylogenies of Enghoff et al. (2011Enghoff et al. ( , 2013)).According to Enghoff et al.

ENGHOFF H. et al., A new genus of mongoliulid millipedes from the Far East of Russia
(2015) Mongoliulidae differ from Parajulidae by having the claw of the first male legs absent or reduced, the second pair of male legs at most moderately modified, the penis unpaired, the seventh pair of male legs with enlarged coxae and modified and/or size-reduced telopodites (exception: Ussuriiulus), and the anterior gonopods mostly with flagella (reduced to tiny flaps in Kopidoiulus, missing in Ussuriiulus and (?) Ikahoiulus).
Additional distinguishing characters of Mongoliulidae are: Eyes present or absent.Surface of metazonites clearly striate only below ozopore level.The first pair of male legs enlarged (exception: Ansiulus deminutus Mikhaljova, 2001) and modified to a varying degree.The second pair of male legs  2017) normal (exception: Koiulus gen.nov.), somewhat reduced in size, coxae prolonged.Anterior gonopods with coxal processes, flagella and reduced telopodites.Posterior gonopod with or without telopodites.
Koiulus gen.nov. shares all the diagnostic characters of Mongoliulidae including the reduced claw of the first pair of legs, the unpaired penis, the modified seventh male legs and possibly also the presence of flagella, although these seem to be strongly modified.
Table 1 shows a comparison of Koiulus gen.nov.with the seven already described genera of Mongoliulidae.
The new genus seems to be especially similar to the genera known from the Far East of Russia, Ansiulus, Skleroprotopus, Kopidoiulus and Ussuriiulus, in the structure of the male gnathochilarial promentum, the first and seventh pairs of male legs (however, the latter is unmodified in Ussuriiulus), separate coxal processes and the relatively long telopodites of the anterior gonopod.With Kopidoiulus, Ikahoiulus and Ussuriiulus it shares the reduced to absent flagella, and with Ussuriiulus it shares the peculiar lack of ozopores on certain body rings, a condition unknown in all other juliformian millipedes.(In the original description of Uenoiulus notabilis Murakami, 1971, there is a drawing of the anterior end of the holotype male in which the ozopore seems to be missing from body ring 7. We have examined four male and two female paratypes of U. notabilis and have found that ozopores are present in a continuous series starting from ring 6, but in males, where ring 7 is very narrow, the pore is difficult to see.) On the other hand, the new genus stands out by the strongly modified second pair of male legs.Species of Ansiulus, Skleroprotopus and Kopidoiulus appear to be morphologically rather variable (Mikhaljova 1997;Mikhaljova & Korsós 2003).The male leg-pair 7 and the gonopods are most often subject to variability.As regards the male leg-pair 7, the number of segments of the telopodite is particularly unstable and variability may even occur between both sides of the same specimen (Mikhaljova & Korsós 2003).In Koiulus interruptus gen.et sp.nov. the number of segments of male leg 7 ranges from 3 in the males from the upper course of River Ko to 4 in the male from the environs of Zolotoi village.
The close resemblance, including gonopodal characters, between Ansiulus and Skleroprotopus, in combination with the high variability in some species, might be evidence for the synonymy of these genera.The same applies to Kopidoiulus and Ikahoiulus.This will be discussed in a separate article (Mikhaljova in prep.).

Postembryonic development
Fig. 2 clearly shows that males are thinner than females with similar numbers of podous rings.Interestingly, smaller juvenile males seem to follow the same "growth-pattern", expressed as "diameter per podous ring" as females, whereas adult males, as well as larger juvenile males, are thinner than females, the difference increasing with increasing numbers of podous rings.It thus seems that the development of a more slender body in adult males is coupled to the onset of maturity.This tendency was also observed in the genus Cylindroiulus Verhoeff, 1894, family Julidae by Enghoff (1982).
The implications of the missing defence glands for interpretation of postembryonic growth will be discussed in a separate article.

Fig. 2 .
Fig. 2. Koiulus interruptus gen.et sp.nov.Body size as expressed by number of podous body rings and midbody diameter.

Table 1 (
continued on next page).Comparison of mongoliulid genera.H. et al., A new genus of mongoliulid millipedes from the Far East of Russia kindly arranged a loan of Uenoiulus notabilis paratypes, to Anders Illum who assisted with photography and scanning electron micrography, to Mrs Galina Sinelnikova (Vladivostok, Russia) who kindly inked Fig.6, and to Dragan Antić and Sergei Golovatch for careful reviews of the manuscript. ENGHOFF