A new species of alderfly (Megaloptera: Sialidae) is described and figured from a rare adult specimen preserved in middle Eocene (Lutetian) Baltic amber. Sialis (Protosialis) voigti, new species, is distinguished from the two other species of Protosialis recorded from Baltic amber. The Megaloptera documented from Baltic amber are briefly overviewed and the geological history of Sialidae summarized.
Introduction
The Megaloptera (alderflies, dobsonflies, and fishflies) are relatively primitive members of the holometabolan superorder Neuropterida, notable for the plesiomorphic retention of a broad anal region in the hind wing. The order consists of about 275 species distributed throughout the world and segregated into two modern families—the large and robust Corydalidae (dobsonflies, fishflies), and the more diminutive Sialidae (alderflies). Larvae of both families are aquatic and generalist predators of small invertebrates. The final-instar larva emerges from the water and pupates in a chamber dug into soft soil. The adults are relatively short-lived, some living merely a week, and spend almost all of their time in vegetation near water.
Since Megaloptera are essentially aquatic insects, at least in their immature stages, their occurrence in Baltic amber is not common. Indeed, only 15–20 inclusions of adult Megaloptera seem to be known. Remarkably, two mature larvae are also known as amber inclusions, both of the family Sialidae—the first recorded by Weidner (1958; Weitschat and Wichard, 2002), the second nearly a half a century later by Wichard (2005: fig. 1). These larvae were almost assuredly entombed shortly after leaving the water and while attempting to find a suitable location for a pupal chamber. In total the Baltic amber fauna contains seven species of Megaloptera, summarized in table 1.
Herein we provide the description of a new species of alderfly recently recognized in Baltic amber. The new species belongs to the modern genus Sialis and the subgenus Protosialis in particular, and is known from two adult females. Morphological terminology and venational nomenclature follow that employed elsewhere for Megaloptera (e.g., Wichard, 1997, 2002). The age and origin of Baltic amber has been reviewed by Weitschat and Wichard (2002) and Grimaldi and Engel (2005).
Systematic Paleontology
Genus Sialis Latreille
Sialis Latreille, 1802: 290. Type species: Hemerobius lutariusLinnaeus, 1758, by monotypy.
Protosialis van der Weele, 1909: 263. Type species: Semblis americanusRambur, 1842, by original designation. [recognized as a subgenus]
Ilyobius Enderlein, 1910: 381. Type species: Ilyobius flavicollisEnderlein, 1910, by original designation. [ = Protosialis]
Nipponosialis Kuwayama, 1962: 329. Type species: Sialis jezoensisOkamoto, 1910, by original designation. [ = Sialis s.str.]
Protosiails Penny, 1977: 9. Lapsus calami pro Protosialis.
Diagnosis:
Adult with head prognathous and relatively flattened; compound eyes large, positioned laterally; ocelli absent; antennae filiform; mandibles strong, multidentate. Pronotum broad (width up to twice length), rectangular or trapezoid; meso- and metathorax of equivalent proportions and design. Legs moderately long and stout; tarsi pentamerous, fourth tarsomere bilobed (and heart-shaped), with fifth tarsomere inserted near base. Wings well developed, with complete venation typical of the order; fore- and hind wings with Sc fusing with R1 before wing apex, R3 forked in Sialis s.str., simple in Protosialis, M1+2 simple; forewing with M3+4 forked (New and Theischinger, 1993). Males with nine, females with seven fully exposed abdominal segments.
Comments:
The foundation for the classification and determination of species of Sialidae are the works of Lestage (1927) and Weele (1909, 1910). Weele (1909, 1910) established Protosialis as a separate genus. Later, Ross (1937) considered Protosialis a synonym of Sialis, and Whiting (1994) considered the group to be a basal subgenus. Today some authors prefer to retain Protosialis as generically distinct, but we consider it as a subgenus pending a comprehensive cladistic analysis of species in Sialidae. Unlike Sialis s.str., Protosialis has R3 simple in both the fore- and hind wings while this vein is forked in the former group (New and Theischinger, 1993).
Sialis (Protosialis) voigti, new species Figures 2–{ label needed for fig[@id='i0003-0082-3513-1-1-f04'] }Figure 6.8
Diagnosis:
The new species shows the diagnostic combination of features typical of the subgenus Protosialis; i.e., R3 and M1+2 are both unforked in the fore- and hind wings and M3+4 is forked in the forewing (New and Theischinger, 1993). The new species can most readily be distinguished from the other Protosialis species in Baltic amber by the combination of R2 forked in both fore- and hind wings and by M3+4 unforked in the hind wing (table 2). In addition, R4 and R5 in both the fore- and hind wings are unforked.
Description:
Female. Total body length approximately 11.5 mm. Integument imbricate and dark brown where evident; wing veins dark brown, membrane hyaline. Head about as long as wide, with large compound eyes positioned laterally on anterior half of head. Mandibles stout; maxillary palpi 5-segmented; labial palpi 3-segmented; other mouthpart structures not discernable. Left antenna with 28 antennomeres (i.e., including scape and pedicel), right antenna partial; flagellomeres of roughly equal size, each slightly longer than wide. Ocelli absent. Tarsi of typical pentamerous construction, with fourth tarsomere bilobed and heart-shaped (distinguishing feature of Sialidae, along with the absence of ocelli). Forewing approximately 14 mm in length; costal field weakly arched, giving wing a slender form; seven c-sc crossveins present before termination of Sc; R1 running parallel with Sc (with narrow subcostal cell between them) before veins merge near wing midpoint; R2 forked near wing apex; R3, R4, and R5 simple at wing apex; M1+2 simple; M3+4 forked near wing apex. Hind wing with R2 forked near wing apex; R3, R4, R5, M1+2, and M3+4 simple (the last vein is easily seen in the right hind wing but challenging to discern in the left hind wing). Female terminalic sclerites as depicted in figure 6; sternite VIII with two, well-differentiated, lateral calli.
Holotype:
Adult female in middle Eocene Baltic amber (figs. 2, 3); accession number KU-NHM-ENT, B-003; located in the Fossil Insect Collection, Division of Entomology, University of Kansas Natural History Museum, Lawrence, Kansas.
Preservation:
The holotype is on one side of a large, oval piece of clear, yellow amber of maximally 39 mm length and 20 mm width, with a mass of 3.3 g. In the immediate vicinity of the alderfly is a partial caddisfly (only the front half of the body preserved, the distal half of the body and the distal third of the wings are cut off) along the amber's edge. The maxillary palps, antennae, and legs permit identification of the caddisfly as a species of Leptoceridae (Trichoptera). The remaining and larger portion of the amber contains fine detritus and numerous stellate trichomes, characteristic of Baltic amber.
The alderfly is in remarkably good condition and, aside from being rather complete, is also well positioned in the amber, permitting detailed examination. The specimen has some Schimmel (a froth of microscopic bubbles) obscuring the integument in some areas, but none of it prevents identification. The right forewing is rather extensively damaged along its leading edge while the left forewing is complete, only slightly obscured near the apex of its posterior margin by the left hind wing being partly folded forward (figs. 4, 5). Both hind wings can be seen in ventral aspect and, despite a few minor folds and some obscuring by the abdomen, the venation can be easily discerned (figs. 4, 5). The legs are complete and preserved folded beneath the body. The right antenna is incomplete, but the left antenna is well preserved. The mouthparts are not easily viewed, except for the palpomeres of the labium and maxilla, which can be distinguished. The venter of the abdomen is easily examined, and the female genital sclerites can be sufficiently discerned (fig. 6).
Additional Material:
An adult female in middle Eocene Baltic amber (figs. 7, 8); specimen in the collection of Jürgen Velten, Idstein, Germany.
Etymology:
The specific epithet honors the late Peter C. Voigt (July 22, 1930–November 25, 2004). Peter was the heart and soul of the Bernstein Arbeitskreis (based in Hamburg), maintaining strong contact with each member and sharing with all his great enthusiasm for every aspect of amber and its study. He is greatly missed.
Comments:
The genital sclerites are typical for species of Sialis (e.g., Ross, 1937; New and Theischinger, 1993; Engel, 2004). Sternite VII is large and sclerotized but is otherwise little modified. Structural modifications are predominantly located on sternite VIII. Typically in Sialidae, sternite VIII forms a narrow, transverse strip with various, species-specific modifications. In S. voigti sternite VIII consists of two calli that are well separated medially (fig. 6). The calli are particularly strong apicolaterally and their form reinforced by a strong medial depression. Tergite IX is enlarged and extends ventrally to the sides such that it can be seen in ventral aspect, the apicolateral margins bordering the gonapophyses of the ovipositor (fig. 6). Subapically on the ventral margin of each gonapophysis is positioned a minute stylus. Cercal calli can be seen lateral to the ovipositor.
Discussion
With the discovery of S. voigti, the number of alderflies in Baltic amber has risen to four and the number of Megaloptera to seven (table 1). Alderflies are exceptionally rare in amber, with only two larval and six adult (including the four holotypes) specimens documented. The two additional adult specimens are recorded as a paratype of S. herrlingiWichard (2002) and the other as a putative S. voigti (herein, vide supra). The putative specimen of S. voigti has only the right forewing recognizable in which it depicts the forked R2 and unforked R3, R4, and R5, unforked M1+2, and forked M3+4 typical for the species. The hind wings, however, are entirely covered, and the rear of the body is damaged and cleared (figs. 7, 8). Thus, definitive placement is not possible, but the evidence from the forewing is strongly suggestive.
Almost all fossil records of sialids are from the Tertiary and almost exclusively from Europe, with single records from Asia Minor and Australia (table 3). The earliest record of an alderfly is Dobbertinia reticulata (Handlirsch, 1925) (Sialidae: Dobbertiniinae) from the Liassic of Germany (Ansorge, 2001). Dobbertinia is plesiomorphic in almost all details for Sialidae but exhibits the characteristic partial desclerotization of MA in the forewing. Unfortunately, an approximately 120 million year gap exists until the next record of a fossil alderfly, a wing fragment of an unnamed Austrosialis from the Paleocene of Queensland, Australia (Lambkin, 1992). A real diversity of sialids is first observed in the Eocene, particularly the fauna recorded from Baltic amber. However, given the extreme paucity of specimens it is impossible to ascertain the true diversity of sialids in the Late Mesozoic or Early Tertiary and whether the family was already well established in during the Cretaceous or, like some other insect groups such as ants, bees, termites, chrysidoid wasps (Grimaldi and Engel, 2005; Engel, 2005), they were present but did not diversify until later in their evolution. Given the low diversity of Megaloptera today it is most likely that they have always been relatively species-poor and in moderate abundance. It is greatly hoped that more complete and extensive material of fossil Sialidae, particularly from the Cretaceous, will eventually be discovered and the evolution of this order more fully understood.
Acknowledgments
We are grateful to Drs. Vladimir A. Blagoderov and Roy J. Beckemeyer for comments on the manuscript; to Mr. Claus Lüer, scientific illustrator in Cologne, for executing the line drawings; and to Mr. Jürgen Velten, Idstein, for permitting us to study Sialis inclusions in Baltic amber from his collection. Partial support for this work has been provided by NSF EF-0341724 (to MSE) and the General Research Fund of the University of Kansas Department of Ecology & Evolutionary Biology (#2301360, to MSE). This is contribution No. 3437 of the Division of Entomology, Natural History Museum, University of Kansas.
References
Figure 1.
Photomicrograph of a mature alderfly larva in middle Eocene Baltic amber (private collection of Mr. Jürgen Velten, Idstein).
Figure 2–3. Photomicrographs of the holotype female of Sialis (Protosialis) voigti, n.sp.2. Dorsal aspect. 3. Ventral aspect.
{ label needed for fig[@id='i0003-0082-3513-1-1-f04'] }
Figure 4–5. Line illustration of the holotype female of Sialis (Protosialis) voigti, n.sp.4. Dorsal aspect. 5. Ventral aspect.
