Siphloplecton picteti Staniczek & Godunko, 2012

Staniczek, Arnold H. & Godunko, Roman J., 2016, Revision of fossil Metretopodidae (Insecta: Ephemeroptera) in Baltic amber — Part 3: Description of two new species of Siphloplecton Clemens, 1915, with notes on the re-discovered lectotype of Siphloplecton macrops (Pictet-Baraban & Hagen, 1856), Zootaxa 4103 (1), pp. 1-24 : 8-14

Siphloplecton picteti Staniczek & Godunko, 2012

Figures 6 A–F, 7A–B, 8A–F, 9A–B

2012 Siphloplecton picteti Staniczek & Godunko, 2012 — Paleodiversity: 63, figs 3a, b (synonymy, description, systematic position)

For complete list of synonyms see Staniczek & Godunko 2012: 59, 63

Here we provide a complementary description of S. picteti based on previously undescribed material.

The holotype of S. picteti ( Staniczek & Godunko 2012) previously belonged to the S. macrops type series ( Pictet-Baraban & Hagen 1856). Demoulin (1968: 250, fig. 14b, c) had designated this specimen as paralectotype of S. macrops , but as the poor condition of the lectotype of S. macrops does not allow any conclusion on the conspecificity of these two specimens, Staniczek & Godunko (2012) described the former paralectotype of S. macrops as a new species, S. picteti .

The holotype of S. picteti is an incompletely preserved male imago without head, thorax and legs. The species was described based on specific characters of left fore- and right hind wings, as well as abdominal segments and genitalia (see Staniczek & Godunko 2012: fig. 3a, b).

The discovery of the first two well preserved specimens of S. picteti now provides the possibility for a detailed description to reassess its taxonomy within other fossil and extant representatives of Siphloplecton . Taking this into account, a complete description of both new specimens of S. picteti is given below.

Usually, the coloration of amber specimens must not be taken into account, as the presence of irregular colored fields, spots, and maculation on wings are results of postmortal changes during the process of fossilization.

However, sometimes traces of pigmentation, especially on the mesonotum are preserved and can be used as an additional distinguishing character. The presumably original coloration of upper and lower parts of male compound eyes (a feature that is almost never preserved in fossil mayflies) is also visible in both specimens of S. picteti described below.

Material. Male imago in Baltic amber (Eocene), SMNS, BB- 100-G.

Well preserved specimen in relatively dark amber, clearly visible in dorsoventral aspect. Lateral parts of thorax and abdomen also visible from left lateral side.

For measurements see Table 3 .

Syninclusions are one Diptera specimen and another specimen of mayflies in very bad condition. In the latter, left side of thorax is not preserved, remaining part of thorax, wings, abdomen and cerci are covered by thick layer of crystallized resin ( Fig. 6 A).

Description. Male imago (SMNS, BB-100-G). General color of body dark, light brown to brownish-black; thorax darkest. Dorsal side of body paler than ventral side. Coloration of head and antennae uniformly brownish, fully preserved. Eyes large, medially contiguous; their dorsal portion is flattened ( Figs 6 B, F). In lateral view, eyes divided into two portions; upper portion slightly paler than lower portion. Ocelli large, well preserved, without traces of pigmentation ( Figs 6 F, 7A).

Sutures of pronotum and metanotum not visible. Mesonotal sutures well preserved: lateroparapsidal suture elongated, without traces of surrounding pigmentation; mesonotal suture medially only slightly bulged, but not transverse ( Fig. 6 F; for comparison see Kluge 2004: 84, fig. 21E, D); furcasternal protuberances fused ( Figs 6 E, 7A).

Forewings only partly translucent and hyaline. Distal half and proximal part of left forewing darkened; right forewing with different color pattern, no pigmentation around transversal veins. The asymmetric arrangement of dark patterns in left and right forewings ( Figs 6 B, C) rather points to an artefact of fossilization than to the characteristic coloration in extant species of the S. basale species group. Right fore- and hind wings partly twisted. Pterostigmatic area hardly visible, at least 2−3 veins forked. Venation of cubital field of forewings is typical of Siphloplecton with two pairs of intercalaries ( Fig. 7 A). Hind wings mainly hyaline, partly damaged, 0.34x length of forewing, with all characteristic triads present; costal process bluntly pointed.

Legs dark, brown to dark brown. For measurements of leg segments see Table 3 . Left forelegs completely preserved; row of sharply pointed setae on outer margin of foretibia. Middle and hind legs paler than forelegs. Left and right middle leg clearly differs in their proportions due to an underdeveloped right middle leg. Trace of tibiopatellar suture visible on tibia of middle and hind legs. Tarsi 5-segmented; first segment of middle and hind legs fused with tibia. All tarsal claws dissimilar, ephemeropteroid.

Abdominal segments completely preserved. Shape of styliger plate as in holotype of S. picteti : angulate, mediocaudally incised; medially with small, triangular projection; incision medially to each gonostylus bordered by a prominent, lateral, triangular projection. Basal segment of forceps nearly square, apically with prominent hump on inner margin; base of basal segment narrower than adjoining apical part of styliger plate ( Figs 6 D, 7B). Forceps 4-segmented; segment 2 longest, segment 4 approximately 2.72 times as long as wide (in holotype of S. picteti —2.58; additional investigation of material in February, 2013); length ratio of segment 3 to segment 4 approximately 1: 0.8 (in holotype approximately 1: 1). Penis short, lobes distinctly rounded at tip; penis lobes only slightly expanding laterally, medially contiguous almost at entire length (except of last 1/7 of visible part of its length); medial and lateral sclerites rounded ( Fig. 7 B).

Cerci partly preserved; paracercus not visible.

Material. Male imago in Baltic amber (Eocene), MNHK, MP/869.

Relatively well preserved specimen. “Verlumung” around head, pro- and mesothorax from ventral and lateral sides. Right side of body partly damaged: right eye flattened; lateral, and partly dorsal and ventral parts of thorax not preserved; right fore- and middle legs lost; left middle and hind legs partly lacking tibia and tarsi. Right forewing medially slightly twisted, venation hardly visible due to influxes of resin and air bubble and due to cracks in the resin on left side. Abdominal segments IV −IX slightly flattened.

For measurements see Table 4 .

Description. Male imago (MNHK, MP/869). Specimen with paler color than previous one, yellowish-brown to light brown, with thorax and last five segments of abdomen darker; terga slightly paler than sterna ( Figs 8 A–C). Head pale, dirty brown; antennae and ocelli of same color. Eyes large, touching medially; division of eyes into two parts is hardly visible; lateral part of left eye only with pale irregular maculation centrally and near of eye base.

Thoracic terga not visible; furcasternal protuberances contiguous ( Fig. 9 A). Wing translucent, hyaline, not pigmented; two pairs of intercalary veins in cubital field of forewings; pterostigma with numerous furcated veins. Costal process of hind wings small and pointed apically ( Fig. 8 D). Hind wing length 0.36x forewing length. Left foreleg the same color as middle and hind legs, yellowish-brown to light brown; tibia and tarsi slightly paler than femora; unclear dirty brown maculation irregularly on the legs ( Fig. 8 F). Leg proportions similar to those in specimen described above. Left foretibia with two stout pointed setae at outer margin. Measurements of leg segments in Table 4 .

Abdominal segments completely preserved ( Fig. 8 C). Shape of styliger plate and penis lobes similar to those in holotype of S. picteti and in specimen described above. Styliger plate with lateral, broad, triangular projections; medial projection small. Basal segment of forceps nearly square, with inner hump apically ( Figs 8 E, 9B). Forceps segment 2 longest, segment 4 approximately 2.70 times as long as wide; length ratio of segment 3 to segment 4 approximately 1: 0.8.

Penis short, with distinctly rounded lobes at tip, medially contiguous almost at entire length; only shallow, broadly U-shaped cleavage apically.

Cerci partly preserved; paracercus vestigial, with segmentation hardly visible.

Comments. S. picteti was preliminarily attributed to the S. basale species group (see Berner 1978: 96) based on shape of penis lobes and setation of outer margin of foretibia ( Staniczek & Godunko 2012). However, S. picteti occupied a relatively isolated position within the extant basale species group. Main differences are: (1) stout setae on foretibia clearly pointed (in contrast to brush-like setae in extant species of basale group); (2) styliger plate mediocaudally deeply incised, with medial projection (no medial projection in extant species); (3) basal segment of forceps nearly square or rectangular with prominent hump on inner apical margin (broad and conical or nearly square, slightly converging towards apex and without any hump in extant species) ( Berner 1978: 96, 105, 108, 129, figs 7−9, 41; Staniczek & Godunko 2012: 59–60, 64, figs 1b, 3b).

As a consequence, we remove S. picteti from the S. basale group and place it within the herein defined S. picteti species group based on shape of styliger plate and penis lobes, and the presence of stout, pointed setae along outer margin of foretibia. The conspecificity of the S. picteti holotype with the male imagines described here can be confirmed by the general shape of genitalia. As the holotype is very damaged (see Demoulin 1968; Staniczek & Godunko 2012), a comparison of other characters is not possible, but we regard the identical genitalia as sufficient to assume conspecificity.

Siphloplecton picteti can be separated from all fossil representatives of the genus Siphloplecton by the shape of genitalia; from S. jaegeri additionally by measurements of body and wings and by different proportions of fore- and hind wings (see Tables 3 , 4 ). Some aspects of the genitalia, especially shape and spatial arrangement of penial sclerites, place S. picteti close to the fossil species S. sartorii sp. nov. and to the extant S. brunneum Berner, 1978 . Siphloplecton picteti markedly differs from S. sartorii sp. nov. by different proportions of forceps segments, and by the different shape of penis lobes (for more details see description of S. sartorii sp. nov. below). Penis lobes of Recent species are distally much more widely separated, whereas lobes of S. picteti are medially contiguous almost at entire length (e.g. Berner 1978: 105, 116, fig. 9; Staniczek & Godunko 2012: 64, fig. 3b; our Figs 6 D, 7B, 8E, 9B). Clear differences between fossil and Recent species are also present in the shape of basal forceps segment, body size, and wing size.

Figures

FIGURE 6. Siphloplecton picteti Staniczek & Godunko, 2012, SMNS, BB- 100 - G, male imago (photographs): A—total dorsal view; B—general dorsolateral view; C—general ventrolateral view; D—genitalia in ventral view; E—head and thorax in ventrolateral view; F—head and thorax in dorsolateral view.

FIGURE 7. Siphloplecton picteti Staniczek & Godunko, 2012, SMNS, BB- 100 - G, male imago (line drawings): A—general ventrolateral aspect; B—genitalia in ventral view.

FIGURE 8. Siphloplecton picteti Staniczek & Godunko, 2012, MNHK, MP / 869, male imago (photographs): A—total lateral view, left side; B—body and wings in dorsolateral view, right side; C—wings and abdomen, dorsal view; D—right hind wing, ventral view; E—genitalia, lateroventral view; F—right hind leg, lateral view.

FIGURE 9. Siphloplecton picteti Staniczek & Godunko, 2012, MNHK, MP / 869, male imago (line drawings): A—head and thorax, ventrolateral view; B—genitalia, lateroventral view.

Tables

TABLE 3. Measurements of Siphloplecton picteti Staniczek & Godunko, 2012, male imago, SMNS, BB- 100 - G.

Characters	(mm)	Characters	(mm)
Length of body	14.00	Segment 5	0.30
Length of right foreleg	18.08	Length of right hind leg	3.44*
Length of femur	3.36	Length of femur	2.52
Length of tibia	3.44	Segment 3	0.36
Length of tarsus	11.28	Segment 4	0.28
Segment 1	2.64	Segment 5	0.28
Segment 2	2.44	Length of left hind leg	6.04
Segment 3	2.56	Length of femur	2.60
Segment 4	2.28	Length of tibia	1.36
Segment 5	1.36	Length of tarsus	2.08
Length of left foreleg	6.76*	Segment 1	0.64
Length of femur	3.36	Segment 2	0.56
Length of tibia	3.40*	Segment 3	0.34
Length of right middle leg	not measured**	Segment 4	0.26
Length of left middle leg	5.58	Segment 5	0.28
Length of femur	1.96	Length of right forewing	not measured**
Length of tibia	1.40	Length of left forewing	14.20
Length of tarsus	2.22	Length of right hind wing	not measured**
Segment 1	0.60	Length of left hind wing	4.80
Segment 2	0.60	Hind/forewings length ratio	0.34
Segment 3	0.44	Length of right cercus	6.80*
Segment 4	0.28	Length of left cercus	6.60*

*—preserved part

**— for explanation see text

TABLE 4. Measurements of Siphloplecton picteti Staniczek & Godunko, 2012, male imago, MNHK, MP / 869.

Characters	(mm)	Characters	(mm)
Length of body	11.50	Segment 2	0.22
Length of left foreleg	6.92*	Segment 3	0.30
Length of femur	2.75	Segment 4	0.17
Length of tibia	2.50	Segment 5	0.22
Length of tarsus	1.67*	Length of left hind leg	2.62*
Segment 1	1.67*	Length of femur	1.87
Length of right middle leg	2.80*	Length of tibia	0.75*
Length of femur	1.70	Length of right forewing	11.30
Length of tibia	1.10	Length of left forewing	11.42
Length of left middle leg	4.65	Length of right hind wing	3.75
Length of femur	1.82	Length of left hind wing	3.75
Length of tibia	1.62	Hind/forewings length ratio	0.33
Length of tarsus	1.21	Length of right cercus	7.42*
Segment 1	0.30	Length of left cercus	8.00*

*—preserved part