Elsevier

Cretaceous Research

Volume 58, March 2016, Pages 118-124
Cretaceous Research

Two new species of mid-Cretaceous webspinners in amber from northern Myanmar (Embiodea: Clothodidae, Oligotomidae)

https://doi.org/10.1016/j.cretres.2015.10.007Get rights and content

Abstract

Two new genera and species of Cretaceous webspinners (Embiodea) are described and figured, both preserved in amber from northern Myanmar. Atmetoclothoda orthotenes Engel and Huang, gen. et sp. nov., is the first fossil representative of the putatively primitive family Clothodidae, and is segregated into its own subfamily, Atmetoclothodinae Engel and Huang, subfam. nov., owing to its primitive retention of a distinct mentum, a quadrate submentum with straight borders, a postocciptal suture that meets the hypostomal sulcus at the posterior tentorial pit, and subgenae that do not meet medially (thus a ventral bridge or gula is lacking), completely symmetrical terminalia, and unsegmented cerci that apically bear a small inner lamellar projection. Litoclostes delicatus Engel and Huang, gen. et sp. nov., is the first definitive fossil of Oligotomidae (not including a subfossil species in Pleistocene copal and which is likely synonymous with an extant taxon), and differs from modern genera in a combination of head, tarsal, and terminalic morphology. The new fossil species double the known Cretaceous fossils and add a further two families to the Mesozoic record for the order.

Introduction

The insect order Embiodea (also known as Embioptera or Embiidina), is one of the smaller polyneopterous lineages, with approximately 400 living species distributed throughout the world, although the real diversity of the group is significantly greater (Ross, 1991, Ross, 2000a). Commonly referred to as webspinners, species spin silk from glands within their swollen probasitarsi, and this silk is used to construct galleries within which individuals live gregariously (Grimaldi and Engel, 2005, Ross, 2000b). Species are slender with females generally paedomorphic and therefore apterous, while males are typically winged. Other distinguishing features of the order include the combination of a prognathous head that is usually closed ventrally by a ventral bridge or gula (but see below); a reduced mentum and large submentum; absence of ocelli; filiform antenna; trimerous tarsi; enlarged metafemur with greatly developed metatibial depressors; plantulae typically present on metatarsomeres I and II; homonomous and dehiscent wings with ‘blood sinuses’ formed around R, Cu, A, and sometimes Sc; abdomen 10-segmented; male terminalia often asymmetrical; ovipositor vestigial; and cerci frequently dimerous (Boudreaux, 1979, Engel and Grimaldi, 2006, Grimaldi and Engel, 2005, Ross, 1970, Ross, 1991). Resolving relationships both of and within the order has been a challenge, and the sundry numerical attempts have revealed that considerable paraphyly or even polyphyly exists throughout the group (e.g., Miller et al., 2012, Szumik, 1996, Szumik et al., 2008). The family Clothodidae, usually recovered as monophyletic, is often considered the earliest diverging of the living lineages (e.g., Davis, 1940, Miller et al., 2012, Ross, 1970, Ross, 1987, Ross, 2000a, Szumik, 1996, Szumik et al., 2008), but even this notion has been challenged and Australembiidae may represent the living sister group to other Embiodea (e.g., Klass and Ulbricht, 2009, Miller et al., 2012). While Embiodea is consistently monophyletic, their placement among Polyneoptera waivers between support for the Mystroptera (Zoraptera + Embiodea) or the Eukinolabia (Phasmatodea + Embiodea) (e.g., Beutel and Gorb, 2006, Boudreaux, 1979, Engel and Grimaldi, 2000, Grimaldi and Engel, 2005, Ishiwata et al., 2011; ; Letsch and Simon, 2013, Rähle, 1970, Rafael and Engel, 2006, Terry and Whiting, 2005, Yoshizawa, 2007, Yoshizawa, 2011). It is clear that considerable work remains to be undertaken concerning the systematics and biology of Embiodea before a consistent system can be developed.

Perhaps not surprisingly given their life history, Embiodea are poorly represented in the fossil record. Virtually all of those species known are documented from inclusions in amber, as well as a subfossil species, Oligotoma westwoodi Hagen, in Pleistocene copal from East Africa and likely synonymous with an extant species (Hagen, 1885: note that this species was referred to by Hagen, 1866; but not named or described at that time). Species have been discovered in the lower Miocene amber of the Dominican Republic (Ross, 2003, Szumik, 1994, Szumik, 1998), the middle Eocene amber of the Baltic region (Pictet, 1854, Ross, 1956), the lower Eocene amber of India (Engel et al., 2011, Rust et al., 2010), and the mid-Cretaceous amber of northern Myanmar (Cockerell, 1919, Davis, 1939a, Engel and Grimaldi, 2006). In addition to these, a compression fossil of a poorly understood species of a putative embiid has been described from the Eocene-Oligocene shales of Florissant, Colorado (Cockerell, 1908, Ross, 1984). Two further compression fossils have been described as stem-group Embiodea from the middle Jurassic deposits of Inner Mongolia, China (Huang & Nel, 2009). Given the scarcity of material, fossils have factored little in attempts to resolve relationships within the order. Nonetheless, given their specialized biology and morphology, particularly the case for the wholly neotenic females, fossil taxa are likely to represent a critical source of information for revealing the historical biogeography and phylogeny of the webspinners. In this context, the discovery and description of any new fossil species is of importance for expanding the available data and from which to ultimately establish broader patterns and explanations (e.g., Grimaldi & Engel, 2007).

Herein we report two new genera and species of mid-Cretaceous webspinners. Both species are preserved in the amber of northern Myanmar, but differ dramatically from Burmitembia venosa Cockerell, 1919 and Sorellembia estherae Engel & Grimaldi, 2006 from the same deposit. The former known species are of the Burmitembiinae (Notoligotomidae) and Sorellembiinae (Pachylembiidae), while the new fossils are representative of the Clothodidae and Oligotomidae, respectively.

Section snippets

Material and methods

The morphological terminology employed for the descriptions is generally that outlined by Ross (2000a) for the order, while the format follows that of Engel et al. (2011). We have followed the general indications of the higher classification suggested by the studies of Ross, 1970, Ross, 2000a, Szumik, 1996, and Miller et al. (2012). The material originates from the Hukawng Valley in northern Myanmar (Cruickshank and Ko, 2003, Grimaldi et al., 2002), and generally considered of earliest

Systematic palaeontology

Order: Embiodea Kusnezov, 1903.

Suborder: Clothododea Engel & Grimaldi, 2006.

Infraorder: Clothodomorpha Engel and Huang, nov.

Family: Clothodidae Enderlein, 1909.

Subfamily: Atmetoclothodinae Engel and Huang, subfam. nov.

Type genus. Atmetoclothoda Engel and Huang, gen. nov.

Diagnosis. Male: Head with postoccipital suture continuous, extending anteriorly on ventral of head to meet hypostomal carina at posterior tentorial pit near posterolateral corners of submentum; ventral bridge lacking, thus

Discussion

The two new genera described herein expand considerably the known fossils of webspinners, doubling the available Cretaceous records and adding two more families to those known from this period. Interestingly, all of the Cretaceous fossils are from Burmese amber (Cockerell, 1919, Engel and Grimaldi, 2006), highlighting the importance of this deposit for understanding mid-Cretaceous insect life. The discovery of putatively primitive species of Clothodidae and Oligotomidae extend the record of

Concluding remarks

As we have documented here, there is a growing diversity of webspinners known from the fossil record and the two genera described double the number of lineages previously known from the Cretaceous. This diversity now includes the primitive Clothodidae, the first of its kind known as fossils as well as from the Eastern Hemisphere, and the earliest occurrence of the Oligotomidae. It is hoped that continued attention to Mesozoic deposits will bring forth additional Embiodea, and that in time a

Acknowledgements

The work of D.-Y.H. has been supported by grants from the National Basic Research Program of China (2012CB821903), the Outstanding Youth Foundation of Jiangsu Province (BK 2012049), and the National Natural Science Foundation of China (91114201). The participation of L.C.V.B. and M.S.E. was partially supported by U.S. National Science Foundation grant DEB-1144162 (to M.S.E.). We are grateful to two anonymous reviewers for their helpful comments on the manuscript. We dedicate this paper to

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