The Earliest Webspinners (Insecta: Embiodea)
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PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3514, 15 pp., 2 figures, 3 tables May 17, 2006 The Earliest Webspinners (Insecta: Embiodea) MICHAEL S. ENGEL1 AND DAVID A. GRIMALDI2 CONTENTS Abstract . ........................................................... 2 Introduction . ....................................................... 2 Systematic Paleontology . ............................................... 3 Order Embiodea Kusnezov . ........................................... 3 Sorellembiidae, new family. ........................................... 4 Sorellembia, new genus. ........................................... 5 Sorellembia estherae, new species. ................................... 5 Family Notoligotomidae Davis . ....................................... 7 Burmitembiinae, new subfamily . ................................... 7 Genus Burmitembia Cockerell . ....................................... 9 Embiodea sp. indet. ............................................... 9 Discussion ........................................................... 9 Acknowledgments . .................................................. 10 References .......................................................... 10 Appendix 1: Current Hierarchical Classification of Embiodea . ............... 14 1 Division of Invertebrate Zoology, American Museum of Natural History; Division of Entomology (Paleoentomology), Natural History Museum, and Department of Ecology & Evolutionary Biology, Dyche Hall, 1345 Jayhawk Boulevard, University of Kansas, Lawrence, Kansas 66045-7163 ([email protected]). 2 Division of Invertebrate Zoology, American Museum of Natural History ([email protected]). Copyright E American Museum of Natural History 2006 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3514 ABSTRACT A new genus and species of webspinner (Insecta: Embiodea 5 Embiidina, Embioptera auctorum) is described and figured from a well-preserved, alate male in mid-Cretaceous (latest Albian) amber from Myanmar (Burma). Sorellembia estherae, new genus and species, is distinguished from the only other Mesozoic webspinner, Burmitembia venosa Cockerell. Unlike the latter taxon, S. estherae embodies an array of notable plesiomorphies for the Neoembiodea (i.e., those Embiodea with strongly asymmetrical terminalia and the tenth tergum divided). Based on its phylogenetic position, S. estherae is placed in a new family, Sorellembiidae. Burmitembia venosa, on the other hand, possesses a synapomorphic suite of traits indicating placement in the Notoligotomidae (sensu novum) and as sister to the apterous subfamily Australembiinae (status novus). Past authors have considered Burmitembia as deserving of familial status, but it seems more conservative to combine the geographically restricted and species-poor sister families Notoligotomidae and Australembiidae and to consider Burmitembia as merely a subfamily therein (as Burmitembiinae). The phylogeny, classification, and geological history of the order are briefly reviewed. INTRODUCTION necessary for dispersal such individuals pump hemolymph into the vein cavities, temporarily Among the smaller orders of polyneopteran providing strength to the wing and permitting insects, the webspinners (order Embiodea, flight. Gallery life has likely also been re- approximately 360 species) are among the sponsible for the overall cylindrical body form more biologically and anatomically distinc- of the species, a shape that lends itself well to tive. Embiodeans are principally distributed deftly moving through the confines of tunnels. pantropically, but some species extend into Together with the orders Plecoptera and warm temperate or marginally into semixeric Zoraptera, the webspinners comprise the super- regions. Where known, species are gregarious, order Plecopterida within the Polyneoptera much like the closely related zorapterans. (Grimaldi and Engel, 2005). This clade is Individuals construct galleries from silk ex- unified by the reduction and loss of the truded from glands inside modified and ovipositor, suppression of male styli, presence enlarged probasitarsi. It is the presence of of an episternal sulcus on the trochantin, these glands that serves as the hallmark reduction in number of tarsomeres, and the synapomorphy for the order, although embio- presence of a ventromedian ostia in the deans are not without numerous other dis- dorsal vessel (unknown for Zoraptera). tinctive and derived traits. In addition to the Embiodea and Zoraptera are most closely probasitarsal glands (and associated modifica- related as evidenced by the secondary re- tions of the probasitarsus) and silken galleries, duction of the vannus to form a narrow, the embiodeans are noteworthy for their paddle-shaped wing; the enlarged metafe- trimerous tarsi, prognathous head closed mora with enlargement of the metatibial ventrally by a gula, absence of ocelli, and depressors (versus the metatibial levators in specialized and reduced wing venation. The other lineages); dehiscent wings; presence of apomorphic peculiarities of the wings, when apterous morphs; and gregarious behavior present (most embiodeans are apterous), are (Engel and Grimaldi, 2000; Grimaldi and associated with life within the network of Engel, 2005). silken tunnels in webspinner galleries. The For such a highly autapomorphic lineage venation is generally reduced, with few cross- one would expect paleontological data to veins, and for the most part desclerotized with provide the most critical insights into its sinuses running through some of the longitu- phylogenetic affinities. Unfortunately, as dinal veins. Thus, rather than forming rigid might be expected for a lineage of small, airfoils, the wings are flexible and collapsible. soft-bodied, terrestrial arthropods the geo- This flexibility permits winged males to re- logical record of Embiodea is poor. Several verse direction in tunnels without the wings Tertiary fossils have been described, almost becoming entangled in the silk and posing an exclusively from middle Eocene Baltic or imposition to movement. When flight is Early Miocene Dominican amber (Ross, 2006 ENGEL AND GRIMALDI: CRETACEOUS EMBIODEA 3 1956, 2003b; Szumik, 1994, 1998), but a single DIAGNOSIS : Small to moderate-sized hemi- compression fossil is also known from the metabolous neopterans with typically slender, Eocene-Oligocene boundary of Florissant, somewhat elongate bodies and short legs. Colorado (Cockerell, 1908; Ross, 1984a). Head prognathous, ventrally closed by gula The sole Cretaceous record of a webspinner between submentum and occipital foramen; was Burmitembia venosa Cockerell (Cockerell, mouthparts mandibulate; mentum reduced; 1919; Davis, 1939a), from the Burmese amber submentum enlarged; dorsal paraglossa flexor deposits of northern Myanmar. The age of present (also in Phasmatodea); compound these deposits had been debated as being eyes present, albeit typically not well de- either Late Cretaceous (e.g., Cockerell, 1917) veloped; ocelli absent; antennae filiform (12– or Eocene (e.g., Stuart, 1923), but recent 32 segments). Legs generally short; trochantin- evidence has demonstrated Burmese amber episternal sulcus present; tarsi trimerous; to originate in the mid-Cretaceous (Zherikhin probasitarsus greatly enlarged and containing and Ross, 2000; Grimaldi et al., 2002; silk glands (for gallery construction); metafe- Cruikshank and Ko, 2003). Putative Paleo- mur enlarged, with greatly developed metati- zoic records of Embiodea are discussed later bial depressors (as in Zoraptera); metabasi- (vide Discussion, infra). Table 1 lists the des- tarsus and metatarsomere II typically with cribed fossil Embiodea. plantulae; pretarsal claws simple. Females Herein we present the description of a sec- apterous (generally paedomorphic); males ond Burmese amber webspinner. Although frequently winged, but shed wings; wings apomorphic within the order the new fossil is homonomous, dehiscent, with reduced vena- considerably dissimilar to Burmitembia and tion; veins weak except R, Cu, and A typically modern webspinners and is described in a new thickened; blood sinuses formed of R, to family. Morphological terminology generally a lesser extent around Cu and A, sometimes follows that of Ross (2000a) except in vena- also weakly around Sc; Sc terminating before tional nomenclature. wing midpoint; stems of M and Cu fused at base; jugal lobe absent. Abdomen essentially SYSTEMATIC PALEONTOLOGY 10-segmented (eleventh metamere is vestigial represented solely by cerci); first abdominal ORDER EMBIODEA KUSNEZOV sternum reduced; cerci typically dimerous (cercal segments sometimes apomorphically Embiodea Kusnezov, 1903 [August]: 208. Originally fused, or with distal segments vestigial), proposed as suborder within Neuroptera. typically asymmetrical in males; gonostylus Embiaria Handlirsch, 1903 [October]: 733. absent; ovipositor absent; eggs tubular, with Oligoneura Bo¨rner, 1904: 526. Originally proposed as slanted and rimmed operculum. Gregarious; suborder within Isoptera. Embioptera Shipley, 1904: 260. Also proposed as living in silken galleries (produced by proba- French vernacular, Embiopte`res, by Lameere sitarsal glands) under bark, stones, or in soil. (1900). COMMENTS : A universally employed name Adenopoda Verhoeff, 1904: 196. for this order, like some others, is not yet Embidaria Handlirsch, 1906: 33. fixed. Although there are no rules governing Aetioptera Enderlein, 1910: 171. Partim (5 Embiodea + Isoptera). Embiidina Enderlein, 1910: 172.3