Oryctochlus kaluginae, Lukashevich, 2012

Lukashevich, Elena D., 2012, Pupae of Mesozoic Oryctochlus Kalugina, Į 985 (Chironomidae: Podonominae), with description of two new species, Fauna norvegica 3, pp. 59-65 : 62-65

Oryctochlus kaluginae n. sp.

Material examined

Holotype: PIN4270 /2442 (well-preserved pupa); SW Mongolia, Shar Teg (outcrop 443/1); Late Jurassic.

Diagnosis (Figures 1F, 2C, D, 3A, B)

Measurements (mm). Total length 5.6, anal lobe length 0.6, width 0.25, thoracic horn length 0.7, width 0.5. Pupa light brown, uniformly coloured (cephalothorax sligthly darker with dark leg sheaths). Thoracic horn (incompletely preserved) large, approximately 1.4x as long as wide, subequal to segment IX width, 0.7x as wide as segment VIII. Wing sheaths wide, without nose, not tapering. Sternites II-VIII with sharply delineated apophyses. Apicolateral lobes of segment VIII short, about 1/5 of total length, enveloping 1/6 of segment IX. Anterior LS setae at 0.5 length from base of VIII segment. Anal lobe elongated, 2.4x as long as wide, with strongly divergent inner margins, outer margins with small denticles. Genital sacs of females not reaching 2/3 of anal lobe length, ending beyond to distal of two setae in mid-section.

Remarks

The new species is close to O. longilobus (Figures 1B, C, K) in the shapes of segments VIII and IX, the chaetotaxy, and the presence of small denticles on the anal lobe outer margins but is different in the shape of thoracic horns.

Etymology

Named in the memory of N.S. Kalugina, an outstanding Russian paleoentomologist.

DISCUSSION

More than a hundred impressions of adult and immature Oryctochlus have been found at the type locality of Uda, indicating that the genus is lacustrine ( Kalugina & Kovalev 1985). Among numerous impressions of Oryctochlus vulcanus Kalugina found larvae with translucent thoracic horns and pupae with translucent male genitalia, which allowed to confidently associate the larvae and pupae and, with some doubts, the pupae and adults. Kalugina compared every life stage of Oryctochlus with those of recent Trichotanypus and drew the conclusion of undoubted affinity of these two podonomine genera, based mainly (but not exclusively) on the peculiar shape of the pupal segments VIII and IX and their chaetotaxy. Among characters of other life history stages, the larvae of O. vulcanus have very long procerci (almost 10x as long as wide), typical of Podonominae . It is worth mentioning that a recent time-calibrated molecular phylogenetic study has recovered Trichotanypus as one of the oldest recent podonomine genera, which split off from Parochlini in the Early Cretaceous ( Cranston et al. 2010).

Re-examination of the type material confirmed the podonomine affinity of Oryctochlus , proposed by Kalugina. This assignment is based first of all on the presence of a plastron plate on the thoracic horn and the arrangement of leg sheaths (all leg sheaths under wing sheath, meeting at tip of wing sheath, distal portion of fore- and midleg sheaths practically straight, S-shaped portion of hind leg sheath beneath distal half of wing sheath – Figures 1H, M). This combination of characters, included by Kalugina in the generic diagnosis, is diagnostic of the subfamily Podonominae ( Brundin 1986) . However, the key evidence is the chaetotaxy of segment IX, which is similar among extant midges only to Trichotanypus . In fact, the segment IX with two broad, apically pointed anal lobes is characteristic not only of Podonominae but also of Tanypodinae (e.g. Telopelopia Roback, 1971 ), and such shape of the segment VIII, with a concave posterior margin, is known not only in podonomine Trichotanypus and Podonomopsis but also in tanypodine Tanypus Meigen, 1803 and prodiamesine Odontomesa Pagast, 1947 .Nevertheless, the anal lobe chaetotaxy patterns of Prodiamesinae and Tanypodinae are quite different: in the former the lobe bears a fringe of lamelliform setae and 3–5 anal macrosetae, grouped in the distal portion of the lobe, whereas in the latter it always lacks distal macrosetae, bearing only two anal macrosetae in the mid-section, sometimes combined with a fringe ( Fittkau & Murray 1986; Saether 1986). Additionally, in Prodiamesinae the thoracic horn has no plastron plate and the leg sheath arrangement is different.

Brundin (1976: 144) described the basic synapomorphy of Podonominae as follows: “Abdominal segments VIII and IX of the pupa in the basic design with strongly enlarged lateral setae which are more or less sharply bent two times in the proximal half and ending in a hook, there being primary 5+5 of these “wavy setae” on segment VIII, 3+3 on segment IX”. In Trichotanypus the wavy setae are weakly developed: “the two bends are only slightly indicated, and the hook-shaped terminal portion is slenderer than the rest of the setae” ( Brundin 1966: 314). Moreover, within the genus their structure also varies: in T. posticalis (Lundbeck, 1898) they are very long, subequal to the length of segment VIII, and distinctly wavy ( Brundin 1966: fig. 443), in T. hanseni Wirth & Sublette, 1970 they are shorter (2/3 as long as segment VIII), with two setae in the mid-section of segment IX almost straight ( Wirth & Sublette 1970: fig. 6), and in T. arctoalpinus Makartshenko, 1983 they are shorter yet (only half as long as segment VIII) and only slightly wavy (some appear straight: Makarchenko 1985: fig. 52).

In her original diagnosis of Oryctochlus Kalugina (1985: 84) wrote about “not long, straight or only slightly curved, not wavy, dark lateral setae” and used this character to distinguish the genus from Trichotanypus . My re-examination of the type material has allowed refining the diagnosis. In fact usually one can see only dark, thick proximal parts of setae, which are straight (Figures 1F, 3A) or slightly curved (Figures 1A, D, G) (see diagnosis), and only occasionally the setae are entirely visible. The specimen PIN 3053/997 was selected as a holotype of O. vulcanus because it shows a pair of thoracic horns attached to the pupa. However, the chaetotaxy is much better preserved on the paratype PIN 3053/959 (negative impression PIN 3053/979; Figures 1A, N, O, 2E). On the segment VIII of that specimen one can see slightly curved long (half as long as segment VIII) setae with thin pale distal part and some of them appear slightly wavy. It is possible that the segment IX bears, besides 3 long lateral setae (2 curved and 1 straight), small straight apical setae (marked with “?” on the Figure 1N) which are obvious on the paratypes PIN 3053/982, 1049 as in Trichotanypus . Even the presence of “black zones” basally on the setae, as recorded in some Trichotanypus and Podonomopsis Brundin, 1966 ( Brundin 1966), can be tentatively surmised for O. vulcanus (Figure 1O). The original figure of the O. longilobus holotype appears to be inaccurate ( Kalugina & Kovalev 1985: fig. 43): the lateral setae on the segment VIII are in fact much longer (half as long as the segment VIII) and some seem to be slightly wavy (Figures 1B, 2F), very similar to those of T. arctoalpinus . Moreover, in both species the anal lobe outer margins are armed with small denticles. Therefore, in the chaetotaxy of the segments VIII and IX the Mesozoic Oryctochlus and the recent Trichotanypus are more similar than was previously supposed (although the lateral setae of the segment VIII of Oryctochlus are not restricted to the apicolateral lobe as in Trichotanypu s) and only the shapes of their thoracic horns are strongly different.

It is worth to mention that, within Trichotanypus , the pupae of different species also differ from each other in the shape of their thoracic horns (the stalk enlarged basally in T. posticalis and tapering proximally in T. hanseni ) and occurrence of apical marginal denticles (present in T. posticalis and T. arctoalpinus , absent in T. hanseni ). Both broad and slender thoracic horns also occur in some other podonomine genera such as Podochlus Brundin, 1966 .

Admittedly, the thoracic horns of Oryctochlus differ from any figured by Brundin (1966) for Podonominae . He considered the thoracic horns of some species of Parochlus Enderlein, 1912 , with the stalk strongly sclerotized, straight and tapering proximally and the plastron plate well-developed, widened distally as the most plesiomorphic. Only the thoracic horn structure of O. longilobus (Figure 1K), with the plastron plate poorly visible, can fit this description, but it is more likely that its horn is not trumpet-shaped but distally round with a moderate plastron plate. In other species of Oryctochlus the plastron plate appears not as large, and the widest part of the horn is not apical (incidentally, as in Trichotanypus ). However, because thoracic horns vary strongly within this subfamily these differences may be of little importance. Within recent Parochlus one can find not only the “ideal plesiomorphic” horns but also very peculiar horns of P. tubulicornis Brundin, 1966 , tapering distally, with a very slender bent stalk and small, strongly reduced plastron plate at the rather narrow tip (similar to the very small plastron plate on the thoracic horn of Trichotanypus posticalis ).

Therefore, contrary to Veltz et al. (2007), there are no reasons to doubt the podonomine affinity of Oryctochlus .

ACKNOWLEDGMENTS

I am deeply indebted to Dmitry Shcherbakov (Paleontological Institute RAS, Moscow) and Andrey Przhiboro (Zoological Institute RAS, St.Petersburg) for valuable discussion and Roman Rakitov (Paleontological Institute RAS, Moscow) for assistance in taking scanning electron images and proofreading the manuscript. I also thank to anonymous reviewers for valuable comments on the early manuscript. The research was partly supported by the program of the Presidium of the Russian Academy of Sciences “Biosphere origin and evolution of geobiological systems” .

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