Tikuna, Savage & Flowers & Porras, 2005

Savage, Harry M., Flowers, R. Wills & Porras, Wendy, 2005, Rediscovery of Choroterpes atramentum in Costa Rica, type species of Tikuna new genus (Ephemeroptera: Leptophlebiidae: Atalophlebiinae), and its role in the " Great American Interchange ", Zootaxa 932 (1), pp. 1-14 : 2-4

Tikuna new genus ( Figs. 1–25 )

Type species. Choroterpes atramentum Traver 1947:156 , here designated.

Imago: male eyes ( Fig. 3 ): upper portions on very short, wide stalk; upper portions contiguous on meson of head; dorsally upper portions circular with small square, facets, facet color yellowish tan; from lateral view, maximum length of lower portions 0.7 maximum length of upper portions; facets of lower portions small, hexagonal, black. Female eyes ( Fig. 4 ): separated on meson of head by a distance 2.5 times maximum width of an eye; margins of head and eyes posterolaterally extended: facets small, hexagonal, black. Ocelli with basal portion dark, apical portion light; lateral ocelli enlarged. Wing size: maximum width of forewings 3/10 maximum length of forewings; maximum length of hind wings 1/8 maximum length of forewings; maximum width of hind wings 0.54 maximum length of hind wings. Forewing ( Fig. 1, 5 ); vein Rs forked 1/5 distance from base of vein to margin; vein MA forked approximately 1/2 distance from base of vein to margin, stem of MA sagged so MA fork often slightly asymmetrical, vein MP forked asymmetrically or MP 2 attached MP 1 by crossveins; ICu 1 attached at base to CuA; crossveins moderately numerous; stigmatic crossveins not anastomosed, marginal intercalaries along posterior margin. Hind wing ( Fig. 2, 6 ): costal projection developed with apex truncate, apex located 3/4 distance from base to apex of wings, base of projection wide; length of vein Sc 4/5 length of wings; apex of wings acute, rounded; crossveins as in Fig. 2 . Legs: all long, length 3/4 length of forewings; ratio of segments of male foreleg: 0.70: 1.00: 0.03: 0.38: 0.39: 0.23: 0.08; claws of a pair similar, with apical hook and opposing lobe ( Fig. 10 ). Abdominal terga 8–9: large and acute posterolateral spines on tergum 9, small rounded posterolateral projections on tergum 8. Styliger ( Fig. 11, 13 ): maximum length 1/3 maximum width; posteromedian margin gently rounded, posterolateral margins developed. Forceps: segment 3 1/2 length of segment 2: segment 2 slightly less than 1/10 length of segment 1; segment 1 with base wider, inner margin of base shaped as in Fig. 11 , inner margin with long, narrow, pointed spines basally and very small rectangular, rounded spins apically; segments 2 and 3 shaped as in Fig. 11 , segment 2 with very small rectangular spines on inner margin. Penes ( Fig. 12 ): short, a little less than 1/2 length of forceps segment 1; basal 1/2 fused, apical 1/2 unfused, mid­lateral margins with projections, apices without appendages. Sternum 7 of female ( Fig. 9 ) with broadly rounded genital extension. Sternum 9 of female ( Fig. 9 ) with large posteromedian indentation and pointed submedian projections. Caudal filaments 1 1/2 to 2 times length of body; cerci and terminal filament subequal in length.

Nymph ( Fig. 14 ) (in alcohol). Body length 6.1–7.5 mm. Head hypognathous, antennae 3 times maximum length of head. Clypeus with lateral margins straight, tapered apically, anteromedian margin straight to slightly convex. Labrum ( Fig. 19 ): maximum width approximately equal to width of distal portion of clypeus; dorsum with apical setae, venter with setae submedially and laterally. Mandible: outer margin of left mandible ( Fig. 20 ) relatively straight, outer margin of right mandible broadly curved; outer incisors with 4 teeth, inner incisors with 2 teeth; outer incisor of right mandible broad with 3 apical teeth and 1 tooth on inner lateral margin, and prostheca as in Fig. 20 . Hypopharynx ( Fig. 22 ): lingua lacking lateral processes, lingua widened distally with broad, median indentation; superlinguae with apical setae. Maxilla ( Fig. 21 ): galea­lacinia with an inner subapical row of 6 pectinate setae, inner apical margin with 1 large pectinate seta and 1 large nonpectinate apically curved seta. Inner lateral margin with a row of long setae and a recessed row of 10 setae near apical margin, apical seta of recessed row larger, thick; segments 1–3 of palpi subequal; setae as in Fig. 21 . Labium ( Fig. 23 ): segment 3 conical with spine­like setae on inner margin, dorsum with a diagonal row of large setae medially, venter with narrow hair­like setae on outer margin and on ventral surface; segment 2 with hair­like setae on outer margin and on inner apical margin; segment 1 shaped as in Fig. 23 , with setae on inner and outer margins, setae on outer margin thicker; paraglossae and glossae with dense setae as in Fig. 23 ; glossae broadly curved over ventrolaterally, large; paraglossae broadly rounded laterally; anterolateral corners of submentum weakly swollen, median area of basal margin gently rounded, lateral margins of submentum without setae. Legs: hind legs longer than fore­ and mid legs, forefemora shorter and slightly fatter to fatter (greater width/length ratio) than mid and hind femora, femora indented on apical 2/5 of inner margin so tibiae can draw partially into femora, maximum width of tibiae 1 1/3 times maximum width of tarsi, inner and outer margins of femora and inner margins of tibiae and tarsi with thick setae, inner basal margin of forefemora with a row of setae, mid and hind tibiae without numerous thick setae on outer margin and medial area, outer margins with scattered long hair­like setae; foreclaws ( Fig. 15 ) weakly hooked and narrow apically, with a basal group of 5–6 narrow pointed denticles along inner margin, denticles slanted, directed anterolaterally, increasing in size apically; and a subapical row of 5 narrow pointed denticles also increasing in size apically. Gills ( Fig. 16–18 ): gills on segments 1–7; ventral lamina of gills 4/5 to subequal to length of dorsal lamina, tracheae of gills branched; gills on segments 2–6 similar ( Fig. 17 ), dorsal lamina with outer basal margin developed anteriorly, ventral lamina with inner basal margin developed anteriorly, apical margin of both laminae with large inner lobe, small outer lobe and a narrow median projection; dorsal and ventral laminae of gill 1 ( Fig. 16 ) lanceolate, slender, gradually tapered apically; dorsal and ventral laminae of gill 7 ( Fig. 18 ) similar, lanceolate, except dorsal lamina wider and longer, ventral portion roughly 4/5 length of dorsal portion, dorsal portion with outer median margin developed and abruptly tapering to apex. From lateral view, posterolateral margins of terga and sterna 8–9 form spines. Caudal filaments: basal 3/10 with clusters of long dense setae forming rows, terminal filament with a row of seta on each lateral margin, cerci with a row of seta on inner lateral margin.

Etymology: Tikuna , a Native American tribal name, feminine.

Discussion: Within the Terpides lineage, Tikuna is most closely related to Fittkaulus , from which it can be distinguished by the following combination of characters. In the imagoes: 1) upper portions of male eyes are on very short, wide stalks; 2) penes are short, basal 1/2 fused, apical 1/2 unfused; mid­lateral margins with projections ( Fig. 12 ). In the nymphs: 1) the two series of denticles in the claws are similar in form and contiguous ( Fig. 15 ); 2) ventral portions of gills 2–6 with large inner and outer lobes on apical margins ( Fig. 17 ); 3) ventral lobes of glossae long and outwardly curved ( Fig. 23 ).

Figures

FIGURES 1–13. Tikuna atramentum, imago and subimago. 1, fore– and hind wings; 2, hind wing, enlarged; 3, head of ♂ imago, lateral view; 4, head of ♀ imago, dorsal view; 5, fore­ and hind wings of holotype subimago; 6, hind wing of holotype subimago, enlarged; 7, abdominal terga 1–9 of ♂ imago. 8, abdominal terga 1–9 of ♀ imago. 9, sterna 7–9 of ♀ imago; 10, claws of ♀ imago; 11, genital segments of ♂ imago; 12, penes, enlarged; 13, genital segments of holotype ♂ subimago.

FIGURES 14–18. Tikuna atramentum, nymph. 14, nymph (median caudal filament broken); 15, foreclaw. 16–18, abdominal gills on: 16, segment 1; 17, segment 5; 18, segment 7.

FIGURES 19–23. nymphal mouthparts. 19, labrum; 20, left mandible; 21, maxilla; 22, hypopharynx; 23, labium: left, dorsum; right, venter.

FIGURES 24–25. 24, Geological map of Costa Rica (redrawn from Abratis 1998) showing terranes of the Nicoya Complex (light grey), localities of recent collections of Tikuna atramentum (black squares), and two possible locations for the type locality (question marks). 25, Reconstruction of development of Lower Central America during the late Cretaceous (80 Ma) and early Tertiary (50 Ma) (redrawn from Meschede 1998). The black arrows point to the northern apex of the Costa Rica–Panamá island arc.