Electrocambalidae fam. nov., a new family of Cambalidea from Cretaceous Burmese amber (Diplopoda, Spirostreptida)

A new family, Electrocambalidae fam. nov. of the suborder Cambalidea is described from Cretaceous Burmese amber based on two new genera, Electrocambala gen. nov. and Kachincambala gen. nov. with four new species, Electrocambala ornata gen. et sp. nov., E. cretacea gen. et sp. nov., Kachincambala muelleri gen. et sp. nov. and K. distorta gen. et sp. nov. The specimens are described combining classical light microscopy with drawings and photography, and modern micro-computed tomography (μCT). Morphological characters otherwise obscured are examined and visualized by creating volume renderings and 3D-segmentations from μCT data. Electrocambalidae fam. nov. is characterized by the following character combination: (1) a forward shift of leg pair 3, resulting in an apparently legless 3rd body ring, (2) presence of metazonital setae, and (3) extensive pilosity on the head. Although some of these characters are shared with other Juliformia they are unique in this combination. The described fossils are the oldest and fi rst Mesozoic Spirostreptida and Cambalidea known and ca 70 million years older than previous records of the group.


Specimens and data deposition
Specimens are from the private collection of Patrick Müller (Table 1). All type material were transferred to the collection of the ZFMK. Measurements of the amber pieces were made using a digital caliper.
All data generated is deposited in Morphobank (O'Leary & Kaufmann 2011) under project number 3903 and can be accessed via the following link: http://morphobank.org/permalink/?P3903.

Drawings
Line drawings were made using a camera lucida mounted on a Olympus BX51 light microscope (Olympus Corporation, Tokyo, Japan), with 40-400 × magnification. Line drawings were transformed to ink on transparent paper, with PIGMA MICRON 04, 03 and 005 ink pens (Sakura, Hayward, USA). Line drawings were scanned and edited in Inkscape ver. 1.0.1.

Photography
Photographs of the studied specimens were made using a Canon EOS 7D camera mounted on a magnifier lens, to obtain images at different focus-levels. Image stacking was performed in Zerene Systems Stacker (ver. 1.04).

Results
Class Diplopoda Gervais, 1844 The specimens belong to the Diplopoda based on the following characters: diplosegments; gnathochilarium present.
Subclass Helminthomorpha Pocock, 1887 The specimens belong to the subclass Helminthomorpha based on the following characters: gonopods present; ozopores lateral; mandibular base divided.
Superorder Juliformia Attems, 1926 The specimens are identified as members of the superorder Juliformia based on the following characters: totally fused body rings; leg pairs 8 and 9 modified to gonopods; collum enlarged.
Order Spirostreptida Brandt, 1833 The specimens are identified as members of the extant order Spirostreptida based on the following character combination: architecture of anterior body rings, with a not completely fused 4 th body ring; body ring 4 seemingly legless; gnathochilarium with stipites not mesally fused and spanning along whole length of gnathochilarium.
Suborder Cambalidea Cook, 1895 The specimens are identified as members of the extant suborder Cambalidea based on the following character combination: anterior and posterior gonopod well-developed; gnathochilarium with eumentum and promentum.

Diagnosis
The new family Electrocambalidae fam. nov. differs from the suborder Spirostreptidea by the structure of the gnathochilarium, with a separate eumentum and promentum, as well as by the presence of two pairs of gonopods. Electrocambalidae fam. nov. differs from the cambalidean families Choctellidae and Pseudonannolenidae by the presence of well-developed posterior gonopods (Fig. 1B, G). The new family differs from the Choctellidae and Iulomorphidae by having distinctly arched metazonites from body ring 6 onwards, and long body rings with a length / diameter ratio > 0.7 ( Fig. 1B (1) leg pair 3 moved anteriad, resulting in a seemingly legless body ring 3 in addition to the legless body ring 4 ( Fig. 1B), (2) presence of setation on the posterior margin of the metazonites, and (3) pilosity on the head is not restricted to the labrum, but extends further up frontally on the head (Figs 1D, 3E, 5D).

Etymology
The family name is derived from the Latin word ʻelectrumʼ meaning ʻamberʼ and the taxon Cambalidea, to which the studied fossils belong.

Other genera included
Kachincambala gen. nov.

Diagnosis
Electrocambala gen. nov. differs from Kachincambala gen. nov. by the presence of an accessory spine on the tarsus (Figs 1E, 3G). The anterior gonopod carries two rounded coxal lobes, the coxite is as long as the telopodite, and the outer lobe of the coxite is ⅓ as long as the inner lobe. The apex of the posterior gonopod is curved anteriorly, creating an open channel ( Fig. 1G-H).

Etymology
As for the family. Feminine.  (Fig. 1F), V-shaped striae laterally on the collum (Fig. 1D) and the absence of longitudinal ridges on the body rings. Metazonite on ventral half with 7 longitudinal striae. Metazonite from body ring 4 onwards distinctly arched (Fig. 1A). Body rings 2-5 narrower than collum and following body rings (Fig. 1B). Anterior gonopod coxite more than twice as long as wide, with inner lobe longer than outer lobe, telopodite narrow, as long as coxite.

Other species included
Posterior gonopod simple, as long as anterior gonopod, projecting between inner and outer lobes of anterior gonopod (Fig. 1G-H).

Etymology
From the Latin word ʻornatusʼ meaning ʻornamentedʼ in reference to the net-like ornamentation and striae on the body rings of the species. Noun in apposition.
Other material examined MYANMAR • 1 ♂; same collection data as for holotype; in the collection of Patrick Müller (BuB1962) • 1 ♀; same collection data as for holotype; in the collection of Patrick Müller (BuB1825).
Posterior body rings. Preanal ring without epiproct projecting, with 5 longitudinal lateral grooves and setae. Anal valves with at least 10 marginal setae and up to 8 setae on surface. Subanal scale not projecting over anal valve. Posterior 3-6 body rings legless (Fig. 1A).
Male sexual characters. Smaller and more slender than females (Figs 1A, 2A vs Fig. 2B-C). In male 1 st leg pair present, reduced in size not in segmentation, without tarsal claw. Penis with wide base and curved tip, with short setae (Fig. 1D). Anterior (8 th leg) and posterior gonopod (9 th leg) well-developed, on body ring 7 ( Female sexual characters. Larger and wider than male ( Fig. 2B-C). First leg pair reduced in length and broadened. Vulva not sufficiently preserved for description.

Remarks
Electrocambala ornata gen. et sp. nov. was discovered in one case (ZFMK MYR7370) in the same amber stone as a specimen of Electrocambala cretacea gen. et sp. nov. described below, showing that both species lived in temporal and geographical sympatry, not unlike recent species of the Cambalopsidae in SE Asia (e.g., Likhitrakarn et al. 2020).
Taphonomic features. Anterior body bent as in defence. Secretion of defence fluid (Fig. 2B). Setation not preserved. Legs only partially preserved (Fig. 2B). Characters partly obscured by body. Amber with fissure.
Trunk. Collum slightly curved, covering posterior margin of head. Collum laterally without striae (Fig. 3C, F). Body rings totally fused from body ring 5 onwards, anterior four body rings with sternite free from pleuro-tergite. Metazonites from body ring 6 onwards distinctly arched and wider than prozonite (Fig. 3C). Body rings with several longitudinal ridges. Metazonites ventrally with at least 5 longitudinal striae, posterior margin with 1 or 2 rows of setae (Fig. 3E), ozopores start lateral from body ring 6.
Posterior body rings. Preanal ring without epiproct projecting, with marginal setae. Subanal scale not projecting over anal valve. Posterior body rings and anal valves covered by fungi (Fig. 3D).

Measurements and taphonomy
Measurements. 17.9 mm long, 0.6 mm in diameter.
Taphonomic features. From body ring 8 onwards body rings and anal valves partially covered by white, filamentous substance. Only right side of anterior body visible, left side obscured by leaf, several legs detached, next to body (Fig. 3B).

Measurements and taphonomy
Measurements. 8.4 mm long, 0.5 mm in diameter.
Taphonomic features. Specimen hollow, only sclerotized parts preserved. Only anterior 35 body rings preserved. From body ring 6 onwards only right half preserved. Cracks in amber filled by minerals.

Remarks
This specimen is not sufficiently preserved to identify it as either one of the two species described above, or as a third species. This specimen was identified as a member of Electrocambala gen. nov. based on the following character combination: legs with accessory spine, gap between leg pair 3 and leg pair 4.

Diagnosis
Kachincambala gen. nov. differs from Electrocambala gen. nov. by the absence of an accessory spine on the tarsus (Fig. 5E) and in the structure of the gonopods (Fig. 4F-G).
Etymology ʻKachinʼ, after the Myanmar state of Kachin where the amber deposits are located, and ʻ-cambalaʼ, a common suffix for names in the Cambalidea. Feminine.
Kachincambala muelleri gen. et sp. nov. urn:lsid:zoobank.org:act:F9CC6697-1E02-4A41-AABA-1E5EE46D7AFA Fig. 4 Diagnosis Kachincambala muelleri gen. et sp. nov. differs from the only other species of the genus, K. distorta gen. et sp. nov., in gonopod characters. The anterior gonopod coxite is more stout in K. muelleri gen. et sp. nov., less than twice as long as wide, while it is more narrow in K. distorta gen. et sp. nov. The inner lobe is apically rounded, nearly triangular and bends mesally. The outer lobe of the anterior gonopod is short and broad, oriented more laterally than in K. distorta gen. et sp. nov. Telopodite of anterior gonopod is broad, shorter than coxite. Posterior gonopod simple, broad, reaching over inner lobe of coxite.

Etymology
In honour of Patrick Müller, who granted us access to his large collection of inclusions in Burmese amber for study, which resulted in the discovery of the specimens studied here, and who donated the type material to the ZFMK. Noun in the adjective case.

Description
Habitus. > 41 body rings; cylindrical and slender, up to at least 12 mm long and 0.5 mm wide. Colour dark brown to greyish (Fig. 4A-C).
Trunk. Collum large, laterally with triangular extension. Body rings 2-5 narrower than collum and following body rings. Body rings totally fused from body ring 5 onwards, anterior four body rings with sternite free from pleuro-tergite. Body rings from body ring 5 onwards with distinctly arched metazonite and wider than prozonite. Metazonite ventrally with 7-9 striae. Ozopores from body ring 6 onwards positioned ventro-lateral on metazonite (Fig. 4C).
Posterior body rings. Unknown.
Male sexual characters. Leg pair 1 reduced in size, not in segmentation (Fig. 4A). Anterior gonopod plate-like, coxite with apically rounded inner lobe and shorter outer lobe, which extends laterad. Inner lobe ca two times as long as outer lobe. Telopodite as long as coxite's inner lobe, apically rounded. Presence of flagellum unknown. Posterior gonopod as long as anterior gonopod; apically with rounded lobe extending laterally ( Fig. 4F-G).
Female sexual characters. Unknown.

Measurements and taphonomy
Measurements. Ca 12 mm long, 0.5 mm in diameter.

Description
Habitus. 56 + 4 body rings. Body cylindrical, slender, up to at least 20.8 mm in length, 0.4 mm in diameter. Colour grey to brown (Fig 5A).
Posterior body rings. Preanal ring without epiproct projecting, with few setae. Valves with at least 8 marginal setae. Subanal scale not projecting over valve.
Male sexual characters. In males leg pairs 1 and 2 slightly reduced in size but not in segmentation. In leg pair 2 femur > tarsus > tibia = postfemur = prefemur > coxa. Except leg pair 1 with tarsal claw. Coxa of leg pair 2 inserted medial of coxa of leg pair 1. Paired penis located behind leg pair 2, within pouch. Anterior and posterior gonopods on body ring 7 well-developed, retracted into body. Left gonopods highly deformed (Fig. 5F-G). Anterior gonopod with telopodite slightly longer than coxite, apically pointed. Coxite long, slender, with two lobes, outer lobe pointed and nearly as long as inner lobe. Inner lobe apically rounded. Presence of flagellum unknown. Posterior gonopod longer than anterior gonopod, anterior surface of posterior gonopod with possible seminal groove (Fig. 5F-G).

Remarks
This specimen is identified as a member of Kachincambala gen. nov. based on the absence of an accessory spine. The poor preservation of this specimen prevents any assignment to the species of Kachincambala described here or to describe it as a new species.
Taphonomic features. Anterior body rings compressed. Posterior body rings partly polished away.

Remarks
This specimen is identified as a member of the Electrocambalidae fam. nov. based on the large gap between leg pairs 3 and 4 and the presence of setae on the head and the posterior margin of the body rings. It is determined as a member of Kachincambala gen. nov. based on the absence of an accessory spine. For a detailed description the animal is not sufficiently preserved.

Measurements and taphonomy
Measurements. 13.8 mm long, 0.4 mm in diameter.
Taphonomic features. Body straight. Imprint of body next to specimen. Body dorsally flattened, cuticle partially broken. Layering of amber.

Characters of the Electrocambalidae fam. nov.
The family Electrocambalidae fam. nov. is distinct from all Cambalidea and Spirostreptidea by the position of leg pair 3. Leg pair 1 and 2 both appear to be situated on the collum and leg pairs 3 is shifted to body ring 2 in the Electrocambalidae fam. nov., resulting in an apparently legless third body ring, in addition to the seemingly legless fourth body ring observable in all Spirostreptida. This shift of leg pair 3 is the strongest argument in support of the new family, since it also requires modifications of the muscular and tracheal system, associated to the sternites, carrying the legs.
Electrocambalidae fam. nov. shares with the remaining Spirostreptida the architecture of the anterior body rings. In the Electrocambalidae fam. nov. the pleuro-tergites and sternites of body rings 2 to 4 are not completely fused; thus, the sternites carrying the first three leg pairs are free and separated from the pleuro-tergites. Among the Juliformia (Julida, Spirostreptida, Spirobolida), a free leg pair 3 in combination with four not fully fused body rings is only present in the order Spirostreptida, as pointed out by Verhoeff (1928Verhoeff ( -1932 and Mauriès (1992). In the Julida and the Spirobolida only the anterior three body rings are not totally fused while from body ring 4, which carries a single pair of legs (the third pair in Julida, the fourth pair in Spirobolida), and onwards, the pleuro-tergites and sternites are totally fused (Verhoeff 1928(Verhoeff -1932Mauriès 1992). The Julida have a maximum of only two free leg pairs, while the Spirobolida show a special case within the Juliformia, with three free leg pairs, despite having only three not fully fused body rings (Verhoeff 1928(Verhoeff -1932. Because of the differences in the trunk-ring architecture, Hoffman (1982) did not accept a monophyletic superorder Juliformia but placed the Spirobolida in its own superorder Anocheta Cook, 1895, and the Julida and the Spirostreptida together with the Siphoniulida in the Diplocheta Cook, 1895, a placement not recovered in any phylogenetic analyses (e.g., Sierwald et al. 2003;Blanke & Wesener 2014).
Electrocambalidae fam. nov. shares with the Julida the metazonital setation of the body rings. Metazonital setation is common in species of the order Julida, which usually bear a single row of setae (Enghoff 1981). In the Spirobolida setation of the body rings is only known from the Typhlobolellidae Hoffman, 1969, a troglobitic family . Setae on the margin of the metazonites are characters usually not found in species of the order Spirostreptida . The only exceptions can be found in the Cambalidean genera Hypocambala Silvestri, 1897, of the family Cambalopsidae, and Jamilka Shear, 1973, of the family Cambalidae, which bear single a row of setae or are densely covered by setae on the body rings (Jeekel 1963;Enghoff 1981, Jiang et al. 2021. Enghoff (1981) suggested that the metazonital setation in the Julida is a plesiomorphic character, as could also be the case in the here proposed Electrocambalidae fam. nov. Furthermore, in the Electrocambalidae fam. nov. setation of the head is present on the labrum and extends up to the anterior margin of the collum. Within Spirostreptida a similar setation pattern of the head can only be observed in a few species of the genus Hypocambala (Jiang et al. 2021).
The following characters of the Electrocambalidae fam. nov. are shared with the Cambalidea: (1) the structure of the gnathochilarium, (2) the structure of the gonopods, and (3) developmental characters (euanamorphosis, as indicated by the presence of apodous body rings in front of the telson in mature specimens).
(1) The gnathochilarium of the Electrocambalidae fam. nov. corresponds to the state found in several cambalidean families and differs markedly from the structure found in the Julida and Spirobolida. The gnathochilarium of the Electrocambalidae fam. nov. consists of the lateral stipites, which reach over the full length of the gnathochilarium. A basal eumentum and an anterior, triangular promentum are present at its centre. Although the structure of the gnathochilarium is highly variable within the families of the Cambalidea, the structure seen in the Electrocambalidae fam. nov. can be found in representatives within all cambalidean families (e.g., Schubart 1966for Iulomorpha Porat, 1872Loomis 1938 for Tridere Loomis, 1938;Mauriès1983, 1987 for Podoglyphiulus Attems, 1909 andPseudonannolene Silvestri, 1895). In contrast to the Cambalidea the structure of the gnathochilarium is highly conserved in the suborder Spirostreptidea (Jeekel 1985) and the order Spirobolida , which both have an undivided duplomentum, as well as in the order Julida, which has the mentum and the stipites fused (with the exception of Parajulidae Bollman, 1893 (Jeekel 1985)) and differs clearly from the state in the fossil family.
(2) In the Electrocambalidae fam. nov. the 8 th and 9 th leg pairs on body ring 7 are both modified to well-developed gonopods. Within the order Spirostreptida this character state can only be found in the suborder Cambalidea, as classified by Hoffman (1980Hoffman ( , 1982, consisting of the families Cambalidae, Cambalopsidae and Iulomorphidae. In the Spirostreptidea, Choctellidae and Pseudonannolenidae the 8 th leg pair is modified, and the 9 th reduced or absent (Hoffman 1982;Enghoff et al. 2015). Furthermore, the Electrocambalidae fam. nov. seem to be opisthospermophorous or amphispermophorous with the posterior gonopod, which possibly shows the remnants of a seminal groove, being involved in sperm transfer. In the orders Julida and Spirobolida, and the families Cambalopsidae and Cambalidae, the posterior gonopod is the functional gonopod (= opisthospermophory) and the anterior gonopod serves as claspers or rarely assists in sperm transfer (= amphispermophorous) (Jeekel 1985 for Cambalidae and Cambalopsidae;Enghoff et al. 2015 for Spirobolida and Julida). The Iulomorphidae are amphispermophorous with a tendency towards protospermophory (Jeekel 1985). The families Pseudonannolenidae and Choctellidae, and the suborder Spirostreptidea, which lack a fully developed posterior gonopod, are protospermophorous (Jeekel 1985). Therefore, the ancestral state in the Juliformia is most likely opisthospermophory, with a functional posterior gonopod and an accessory anterior gonopod, as seen in our Electrocambalidae fam. nov., and the shift of the sperm transfer function to the anterior gonopod occurred in the suborder Spirostreptidea, and the families Choctellidae and Pseudonannolenidae.
(3) While most species of the suborder Spirostreptidea are hemianamorphic, with body rings only added to a certain stadium, and further moults taking place without an addition of body rings (Enghoff et al. 1993), in Cambalidea adults show apodous body rings in front of the telson, suggesting euanamorphosis. Body rings are added with every moult until the death of the animal (Enghoff et al. 1993). We suggest that the Electrocambalidae fam. nov. are euanamorphic as well, because males show completely developed gonopods and apodous body rings at the same time. This means that after reaching sexual maturity body rings are still added.
Other characters of the Electrocambalidae fam. nov. are (1) ozopores starting from body ring 6 and (2) a relatively well-developed first leg pair in males. The position of the first ozopores (1) varies within the Juliformia, with few exceptions, between body rings 5 and 6 (Attems 1926;Verhoeff 1928Verhoeff -1932. In the cambalidean families Cambalidae (Reboleira et al. 2015), Cambalopsidae (Korsós & Johns 2009), and Pseudonannolenidae (Iniesta & Ferreira 2013a, 2013b ozopores start on body ring 5, while ozopores start on body ring 6 in Choctellidae (Chamberlin 1918) and Iulomorphidae (Verhoeff 1924;Korsós & Johns 2009), as is the case in the Electrocambalidae fam. nov. A well-developed first leg pair in males (2) can be found in several spirostreptidan taxa (see above). In the studied male specimens the first leg pair was only slightly reduced in size but not in segmentation. Golovatch et al. (2007) stated that the cambalopsid species Glyphiulus costulifer Golovatch, Geoffroy, Mauriès & VandenSpiegel, 2007 is probably the most basal representative of the genus because of the nearly unmodified first male legs (Golovatch et al. 2007), while Enghoff (1981) regarded the presence of unmodified first legs in Julida as reversals. Therefore, it is not clear whether or not the presence of an unmodified first leg pair in the fossil specimens is a plesiomorphic condition. At the moment the relationship of the Electrocambalidae fam. nov. to the remaining Spirostreptida and Juliformia remains speculative. To clarify the phylogenetic position of the Electrocambalidae fam. nov. a phylogenetic reconstruction including a broad sampling of juliformian taxa is needed.
The fossils were found in the present distributional range of the family Cambalopsidae, which are endemic to South-East Asia (Jeekel 1985;Shelley & Golovatch 2011). This does not necessarily indicate a closer relationship between the new family and the Cambalopsidae, as data on the Mesozoic distribution of the Spirostreptida is lacking.

The fossil record of the Spirostreptida
The here described Electrocambalidae fam. nov. are the oldest known fossils of the order Spirostreptida. Thus, there are no other Spirostreptida fossils known from the Mesozoic, and the only known fossils of the order are Protosilvestria sculpta Handschin, 1944 (Cambalidae or Cambalopsidae) from the Oligocene (ca 23.03-33.0 ma) of France (Handschin 1944;Mauriès 1992) and the undescribed pseudonannolenid Epinannolene sp., from 20 my old Dominican amber (Santiago-Blay & Poinar 1992). Twelve specimens, four species, two genera and one family are here added to the fossil record of the Spirostreptida, all from Burmese amber dating back to the Cretaceous, ca 99 ma (Shi et al. 2012). These fossils are ca 70 my older than the previously oldest known Spirostreptida and narrow the gap between the estimated appearance of the order Spirostreptida and suborder Cambalidea ca 514 ma (Shelley & Golovatch 2011). The fossil record of the Juliformia, as for the Diplopoda in general, remains scarce and fragmentary, but the exceptional preservation of millipedes in Burmese amber offers the opportunity to greatly enlarge the fossil record. In the same way representatives of the other diplopod orders can be expected to be found in Burmese amber and widen our understanding of the evolution of the Diplopoda tremendously. and the acquisition of photographs. Peter Rühr (University of Bonn) and Jörg U. Hammel (Helmholtz-Zentrum-Geesthacht) are thanked for SR-µCT data on ZFMK-MYR7368. Henrik Enghoff (Natural History Museum of Denmark) is thanked for discussions. We thank two anonymous reviewers for their comments, which greatly helped to improve the quality of the manuscript. The data presented in this publication are part of the Master thesis of LM in the M.Sc. program Organismic Biology, Evolutionary Biology and Paleobiology (OEP-Biology) at the University in Bonn and was conducted at the ZFMK under the supervision of TW. LM is thankful to Prof. Jes Rust (University of Bonn) for the evaluation of this Master thesis and for encouragement. LM is funded in the scope of the DFG-project "Phylogeny of the Diplopoda: micro-CT scans, morphology and morphometry of all millipede orders" (DFG WE 2479/4-1 and BL 1355/5-1) by Prof. Dr A. Blanke (University of Bonn) and TW.