Siphloplecton studemannae, Godunko, Roman J., Neumann, Christian & Staniczek, Arnold H., 2019

Godunko, Roman J., Neumann, Christian & Staniczek, Arnold H., 2019, Revision of fossil Metretopodidae (Insecta, Ephemeroptera) in Baltic amber - Part 4: Description of two new species of Siphloplecton Clemens, 1915, with notes on the new S. jaegeri species group and with key to fossil male adults of Siphloplecton, ZooKeys 898, pp. 1-26 : 1

Siphloplecton studemannae sp. nov. Figures 8 , 9 , 10 , 11 ; Table 1

Material examined.

Holotype. Female imago in Baltic amber (Eocene), SMNS BB– 2626. Well preserved specimen in clear amber, well visible in dorsoventral aspect. Right foreleg lost; hind wings (especially left wing) twisted. Head and thorax covered by “Verlumung”. Additionally, piece of amber with numerous cracks, thus details of thoracic terga invisible, and thorax only partly visible from ventral side. For measurements see Table 1 .

Paratype. Female imago in Baltic amber (Eocene), MNHK, MP/1626. Partly damaged specimen, visible in ventral aspect. View on body hampered by resin influxes, numerous cracks, and considerable “Verlumung”, so thoracic sutures are hardly visible. Head lost. Pronotum damaged, its structure invisible. Distal part of mesonotum, metanotum and abdominal segments I−IV dorsally covered by plant tissue. Right forewing twisted along its length; left forewing lacks its basal part and distal end. Right foreleg, right middle leg, left middle tarsus, and both hind legs lost. Cerci only partly preserved. For measurements see Table 1 .

Description of holotype.

General colour of body pale, yellow to yellowish-brown. Ventral side of body slightly darker than dorsal side. Ocelli well preserved. Eyes medially separated, but approximated ( Fig. 8A ). Distance between eyes 0.22 × of head width. Antennae complete, slightly longer than head, pale.

Thorax ventrally yellowish coloured by “Verlumung”, mainly in posterior part. Furcasternal protuberances of mesothorax contiguous ( Fig. 8B ); lateral aspect of thorax not visible.

Wings translucent, hyaline, not pigmented. Wing venation well visible only from ventral side; basal part of wings covered by numerous cracks from dorsal side. Cubital field of both forewings with one pair of intercalary veins (iCu2, iCu3) towards CuP and one additional vein (iCu1) near CuA ( Figs 8 C–D , 9 ). Right hind wing hardly visible, twisted; left hind wing completely preserved with three pairs of triads, 0.34 × of right forewing length. Costal process bluntly pointed apically and small ( Fig. 8E ).

Legs relatively well preserved, except forelegs (right is lost; left incomplete). Measurements of leg segments in Table 1 . Tibiae of middle and hind legs each with trace of tibiopatellar suture; first tarsomere of middle and hind legs fused with tibia ( Fig. 8F ). Tarsi with 5 tarsomeres; tarsal claws dissimilar: one hooked and one blunt ( Fig. 8G ).

Abdominal segments completely preserved, pale; terga VIII–X slightly darker than remaining terga. Abdominal sterna slightly covered by “Verlumung”. Subgenital plate relatively broad, 2.00 × as wide as long, convex and rounded apically. Subanal plate not elongated, narrow, with pointed tip ( Figs 8H , 9 ). Paracercus poorly visible, vestigial, with at least 4 visible segments; cerci dark, partly preserved.

Description of paratype.

Body colouration light, yellowish-brown to brown. Irregular brown, dirty brown to black maculation over body, especially on forewings and legs ( Fig. 10A ).

Details of mesonotum hardly visible; mesonotal suture typical for Siphloplecton , original lateroparapsidal suture colouration invisible due to resin influx. Furcasternal protuberances contiguous, distinctly brown; other parts of mesosternum paler.

Pterostigma with anastomosed crossveins. Cubital field of right forewing well preserved; iCu1 basally connected to CuA and iCu2 by crossveins, 2 additional CuA-iCu1 crossveins present. Pair of intercalaries iCu2 and iCu3 basally connected to each other; further crossveins connect to CuA and CuP ( Figs 10B , 11A ). Hind wings relatively long, approximately 0.40 × of length of preserved right forewing; costal processes hardly visible. Hind wings with triads RS, MA and MP; costal process (visible only on right hind wing) small and blunt ( Fig. 10C ).

Left foreleg intensely brown to blackish distally; middle legs paler, yellow to yellowish-brown. Preserved foreclaw dissimilar (one claw hooked, one claw blunt).

Most of abdominal segments ventrally covered with “Verlumung”. Preserved sterna paler than terga. Subgenital plate not elongate, approximately 1.80 × wide as long, widely rounded apically. Subanal plate not elongate, pointed at tip ( Figs 10D , 11B ). Paracercus 5-segmented.

Comments.

We allocate Siphloplecton studemannae sp. nov. within the S. jaegeri species group based on the presence of three distinctive intercalaries (grouped in one pair and one additional intercalary vein) in the cubital field of both forewings. The same arrangement of intercalary veins was described and figured for the holotype of S. jaegeri by Staniczek and Godunko (2012: 73, 74, fig. 10b). Other diagnostic characters of this species group, namely the presence of sharply pointed setae at the outer margin of the foretibia, cannot be observed in the type specimens of S. studemannae sp. nov. So it cannot be excluded that this character is present in the females of this fossil species, similarly to the different occurrence of this character in the two sexes of extant species ( Berner 1978).

The new species can be characterized by the presence of the following characters: (1) eyes separated, but close-set; (2) cubital field of forewings with one pair of intercalaries and one intercalary vein connected with CuA; (3) subgenital plate relatively broad with width/length ratio 1.80−2.00. This combination of characters definitely separates the described females of S. studemannae sp. nov. from all other previously known Recent and fossil taxa.

Siphloplecton studemannae sp. nov. is currently the only species of the genus Siphloplecton described from female specimens that can also be attributed to a certain species group. This is only possible due to the unique arrangement of cubital intercalaries, which is characteristic for the S. jaegeri species group. The previously described S. barabani and S. hageni , also only known from female specimens, do not provide any clear distinguishing characters that would allow their placement in one of the other fossil species groups defined for Siphloplecton , which can only be grouped based on similarities in the male genitalia.

Etymology.

Following our tradition of naming new fossil species of Siphloplecton after Swiss ephemeropterists, this species is named after Denise Studemann, Lausanne, to honour her contributions to the knowledge of Swiss mayflies.

Figures

Figure 8. Siphloplecton studemannae sp. nov., SMNS, BB- 2626, holotype, female imago (photographs) A general dorsal view B general ventral view C left forewing in dorsal view D wing base and cubital field of right forewing in ventral view E left hind wing in ventral view F right hind leg in medial view G claws of hind legs H abdominal segments VII-X in ventral view.

Figure 9. Siphloplecton studemannae sp. nov., SMNS, BB- 2626, holotype, female imago (line drawing): abdomen and part of left forewing in ventral view.

Figure 10. Siphloplecton studemannae sp. nov., MNHK, MP / 1626, paratype, female imago (photographs) A general ventral view B left forewing in dorsal view C right hind wing in ventral view D abdominal segments VII-X in ventral view.

Figure 11. Siphloplecton studemannae sp. nov., MNHK, MP / 1626, paratype, female imago (line drawings) A fragments of left fore- and hind wings, dorsal view B abdominal segments VII-X in ventrolateral view.