Potamocloeon edentatum, Kluge, 2019

Kluge, Nikita J., 2019, Potamocloeon edentatum sp. n. from Usambara Mountains in Tanzania (Ephemeroptera, Baetidae), Zootaxa 4648 (2), pp. 299-317 : 304-315

Potamocloeon edentatum sp. n.

( Figs 13–76 )

Etymology. Allusion to absence of the tooth-like projection on the gonostylus, in contrast to Potamocloeon dentatum , which is characterized by «inner basal angle dilated to form a strong tooth» ( Kimmins 1956: 76).

Material examined. Holotype: L-S-I ♂ {specimen [XL](4)2016}, TANZANIA, Tanga Region, Usambara mountains, Amani, upper part of river Sigi , 5°06’S, 38°38’E, 3.IX.2016, coll. N. Kluge & L. Sheyko. Paratypes: the same locality and collectors, 19.VIII–2.IX.2016, 2 L-S-I ♂ , 1 L-S ♂, 4 L/S ♂, 2 L-S-I ♀, 1 L/S ♀, 23 larvae.

Descriptions. Larva. CUTICULAR COLORATION. Head anteriorly brown, dorsally lighter ocher ( Fig. 21 ). Pronotum and mesonotum brown with diffusive lighter areas, fore protopteron light; in last instar fore protopteron darkened in distal part and with brown stripes corresponding to convex longitudinal veins ( Fig. 20 ). Thoracic pleura partly brown ( Fig. 16 ), sterna colorless. Legs mostly colorless, with diffusive brown marking on tibia-tarsal articulation, sometimes with one or two diffusive brown maculae on outer side of femur ( Figs 16–18 ). Abdominal tergum I mostly colorless; terga II–VI mostly brown, with small paired blanks; tergum VII either similar to them, or lighter, sometimes mostly colorless; tergum VIII mostly colorless; terga IX–X mostly brown ( Fig. 19 ). Caudalii mostly colorless, distally with contrasting brown proximal parts of swimming setae ( Figs 22–23 ).

HYPODERMAL COLORATION. Usually invisible through cuticular coloration ( Fig. 14 ); if visible, abdominal coloration similar to that of imago (compare Figs 15 and 61 ).

SHAPE AND SETATION. Frons relatively wide, frontal suture semicircular ( Fig. 21 ). Labrum with pair of long submedian setae and pair of sublateral groups of long setae, about 5 setae in each ( Fig. 25 ). Left mandible ( Fig. 26 ): incisor with long distal denticle, 2 shorter more proximal denticles and short outer-ventral denticle; kinetodontium with long distal denticle and 3 shorter more proximal denticles; prostheca terminated by 3 thick denticles and 3 slender denticles; margin between prostheca and mola either without setae, or with very few and very small setae. Right mandible ( Fig. 27 ): incisor with long distal denticle, 3 shorter more proximal denticles and short outerventral denticle; kinetodontium with long distal denticle and 2 shorter more proximal denticles; prostheca close to kinetodontium, stick-like, apically denticulate; margin between prostheca and mola with setae. Denticles of incisor, kinetodontium and prostheca often worn out ( Figs 26–27 ). Maxilla of « Baetis - type » ( Fig. 24 ): stout, with short biting edge and 3 stout canines; 1st dentiseta stout, similar to canines, bent toward canines. 2d and 3rd dentisetae bifurcate. Maxillary palp 3-segmented. Labium with glossae and paraglossae of equal width. Labial palp with 2nd and 3rd segments of equal width ( Fig. 36 ).

On legs of all pairs, tibia much shorter than femur; fore leg tarsus much longer than tibia (in both sexes), middle and hind legs tarsus as long as tibia ( Figs 16–18 ). Patella-tibial suture on fore leg absent, on middle and hind legs greatly shifted distally, so that runs from midlength of outer side to nearly apex of inner side ( Figs 47–49 ). Legs densely covered with colorless scales in operculated sockets and fewer small hairs ( Fig. 39 ); besides this, with following stout spatulate setae, stout pointed setae and very long colorless hairs:

Stout spatulate setae: Outer side of femur in proximal part with several stout spatulate setae forming irregular row; on fore leg this row terminates proximad of middle ( Fig. 45 ), on middle leg—near middle ( Fig. 46 ), on hind leg—distad of middle; apex of each femur with 2 stout spatulate setae ( Fig. 38 , 45–46 ). Fore tibia with outer-apical spatulate seta ( Figs 47, 50 ); middle and hind tibiae without it ( Figs 48–49, 51 ).

Stout pointed setae: Inner side of each femur with irregularly situated, small, stout, pointed setae. Inner side of each tibia with irregularly situated, somewhat larger, stout, pointed setae; inner-apical angle of tibia with several larger setae of this kind ( Figs 16–18 ). Inner side of tarsus with larger stout pointed setae forming regular longitudinal row; on fore tarsus these setae shifted to anterior side, wider, with both margins serrated ( Fig. 39 ); on middle and hind tarsi these setae smaller, with both margins indistinctly serrated or smooth ( Fig. 40 ).

Very long colorless hairs: Outer side of femur in distal half with regular longitudinal arched row of hairs; on fore leg this row begins just distad of most distal stout spatulate seta (see above) ( Fig. 45 ); on middle and hind legs this row passes anteriad of most distal stout spatulate seta ( Fig. 46 ); this row located on light stripe contrastingly bordered by darker areas of cuticle ( Figs 37–38 ). Tibia with regular U-shaped row of hairs; two arms of this row connected proximally on outer side ( Fig. 38 ); anterior arm stretched longitudinally up to beginning of patella-tibial suture (on middle and hind tibiae – Figs 48–49 ) or to corresponding place (on fore tibia, where patella-tibial suture absent—Fig. 47); posterior arm stretched transversely on fore tibia ( Fig. 47 ), obliquely on middle tibia ( Fig. 48 ) and longitudinally on hind tibia ( Fig. 49 ). Tarsus with U-shaped row of hairs; two arms of this row connected proximally on outer side; both arms stretched longitudinally up to middle of tarsus ( Figs 50–51 ).

Claw without denticles; inner side of proximal half with fine longitudinal striation; distal part with oblique stria- tion ( Figs 41–42 ).

Metanotum with small vestiges of hind protoptera ( Fig. 18 ); median part of metanotum with scales in opercu- lated sockets; posterior margin smooth, without denticles.

Abdominal terga and sterna with scales in operculated sockets ( Figs 43–44 , 53–55 ). Posterior margin of tergum I with few small denticles; posterior margins of terga II–X with long pointed denticles; on tergum IX row of den- ticles interrupted medially, behind submedian pair of setae ( Fig. 44 ). Posterior margins of abdominal sterna I–IV without denticles; posterior margins of sterna V–IX with pointed denticles; in male median part of sternum IX be- tween protogonostyli with dense, palisade, long and blunt denticles ( Figs 43 , 72 ). Each abdominal sternum III–VI or IV–VI with 2–5 long, slender, colorless, bifurcate setae on each side; sternum VII with one pair of such setae ( Figs 52–55 ).

Tergalius I asymmetric, with costal margin most convex in proximal half, and anal margin most convex in distal half ( Figs 28, 29 ). Tergalius II widest, with costal margin slightly convex, and anal margin most convex at midlength ( Fig. 30 ); tergalius V with costal margin most convex distally, and anal margin most convex proximally ( Fig. 33 ); tergalius VII with costal margin convex in distal half, and anal margin slightly convex ( Fig. 35 ); other tergalii intermediate between II, V and VII ones ( Figs 30–35 ). Costal rib on tergalius I short, on tergalii II–VII well- developed and bears 1–5 denticles near apex; anal rib on all tergalii poorly expressed; distal margin and most part of anal margin of each tergalius without rib; middle ribs absent ( Fig. 76 ). All tergalii with central and side tracheae well visible, pigmented.

Caudalii (cerci and paracercus) of equal length, with long and dense primary swimming setae; on paracercus swimming setae located up to apex; cercus with slender apical portion lacking setae ( Fig. 23 ). In middle part of cercus, each 4th segment with several enlarged denticles on lateral side ( Fig. 22 ); paracercus without enlarged denticles. Each swimming seta with proximal half brown and rigid, distal half colorless and delicate ( Figs 22–23 ). Lateral sides of cerci without secondary swimming setae.

RESPIRATORY MOVEMENTS. Tergalii able to make rhythmic respiratory movements.

Subimago. CUTICULAR COLORATION. Pronotum light brown with diffusive blanks, microtrichia darker brown. Mesonotum at most part light brown with darker brown microtrichia; most sutures darker brown; contrasting colorless stripe along medioparapsidal suture and on medio-posterior part of posterior scutal protuberance ( Fig. 57 ). Thoracic pleura and sterna with colorless and brown areas ( Fig. 66 ). Base of wing brownish, other membrane and veins colorless with brown microtrichia. Legs colorless, microtrichia and tarsal microlepides light brownish ( Figs 63–64 ). Abdomen uniformly very light brownish with brown microtrichia; gonostyli lighter. Cerci colorless with setae brown.

TEXTURE. On legs of all pairs of both sexes, all tarsal segments covered by pointed microlepides, only small basal part of fore tarsomere covered by microtrichia (as tibia and other leg segments).

Imago, male. ( Figs 56–60 ). Head ocher with brown. Turbinate eyes with facetted surface and most part of stem brown, upper part of stem just under facetted surface gray, border between stem and facetted surface dark brown. Thorax brown, uniformly colored dorsally, laterally and ventrally. Fore wing with one marginal intercalary per space; pterostigma with 3–5 simple, oblique, complete or/and incomplete veins ( Fig. 13 ); bases of wings brownish, remainder colorless; veins, including costal brace, colorless. Hind wings absent. Legs of all pairs either uniformly ocher, or with diffusive reddish markings as in Fig. 65 . On middle and hind legs tibia slightly shorter than tarsus; first tarsomere (primary 1st+2nd tarsomeres) much longer than others (as in Fig. 65 ). In holotype, relation of fore femur to fore wing length 40:195; proportions femur/tibia/tarsomeres on fore leg 40:49:2:26:20:10:5; on middle and hind legs 30:25:9:4:2:5. Tarsus with one terminal spine on 2nd (primary 3rd tarsomere) tarsomere (as in Fig. 64 ). Abdominal segments I–VII whitish; terga either without markings, or each tergum with diffusive pale reddish unpaired median mark; sterna either without markings, or with small gray unpaired median spot on each joining of segments ( Fig. 60 ); lateral trachea with blackish. Segments VIII–IX with terga brown, sterna whitish, anteriorly bordered by brown; segment X brown. Cerci uniformly whitish.

Male genitals ( Figs 68–72 ). Sterno-styligeral muscle very wide, proximally much wider than distance between median paraproctal muscles, distally wider than distance between unistyligers ( Figs 71–72 ). In imago ( Figs 68, 69 , 71 ), unistyliger with stretched inner-apical margin; first segment of gonostylus of composite shape, with narrowing near midlength; inner-distal angle obtuse; second segment of gonostylus nearly straight, basally narrowed, apically slightly widened; third (apical) segment of gonostylus petiolate, triangular; external part of penis semicircular; penial arms short and thick, with apices bent distally and free (not fused with penial bridge) ( Fig. 71 ). Subimaginal gonostylus without projected inner-apical angle of 1st segment ( Fig. 70 ). In larva ready to molt to subimago, developing subimaginal gonostyli folded as is typical of « Cloeon - type », i.e. with 2nd segments directed laterally ( Fig. 72 ).

Imago, female. Eyes small, widely separated ( Figs 61–62 ). Patella-tibial suture absent on fore leg, present on middle and hind legs (as in Figs 63–65 ) (as in male). Coloration of head, thorax, wings, legs ( Fig. 65 ) and cerci as in male; abdomen ocher; terga II–VI with characteristic reddish-brown markings ( Figs 61–62 ).

Eggs. Irregularly oval, with irregular relief ( Figs 73–76 ).

Dimensions. Fore wing length (and body length) 4.5–5 mm.

Comparison. Male imago of P. edentatum sp. n. differs from P. dentatum (= plumosum ) by shape of first segment of gonostylus, whose inner-distal angle is blunt and not projected distally ( Figs 68, 69 , 71 ). Larva of P. edentatum sp. n. differs by having first pair of tergalii asymmetric ( Figs 28–29 ), while in P. dentatum first tergalius is symmetric, with both costal and anal margins most convex in proximal half (Wuillot & Gillies 1993: fig. 49); in P. abdallahi the shape of tergalii is said to be «as per Wuillot & Gillies (1993)» (McCafferty 2000: 68). Besides this, larva of P. edentatum sp. n. differs from P. dentatum and P. abdallahi by absence of prominent setae between prostheca and mola of left mandible ( Fig. 26 ). Larvae of P. edentatum sp. n. and P. dentatum differ from P. abdallahi by well pigmented tracheae of tergalii ( Figs 28–30 ).

Figures

FIGURES 11–13. 11–12, Potamocloeon dentatum: 11, genitals of subimago; 12, genitals of imago (styligeral and gonostylar muscles shown only on left side, gonoduct shown by dotted line). 13, Potamocloeon edentatum sp. n., fore wing (holotype). Abbreviations: gd – gonoduct; gs1–gs3, segments of gonostylus; m.IX-X, areas of anterior attachment of median paraproctal muscles (i.e., muscles going from sternum IX to common base of paraprocts); m.sg, median sterno-styligeral muscle.

FIGURES 14–23. Larvae of Potamocloeon edentatum sp. n. 14, male larva of last instar with well-developed cuticular coloration; 15, female larva of penultimate instar with light cuticle and well-visible hypodermal coloration; 16, exuviae of fore leg with prothoracic pleurite; 17, exuviae of middle leg; 18, exuviae of hind leg with metathoracic pleurite and part of metanotum (arrow shows vestige of hind protopteron); 19, exuviae of abdomen; 20, exuviae of right half of pronotum and mesonotum; 21, head; 22, portion of cercus and paracercus in middle part; 23, apices of cercus and paracercus.

FIGURES 24–27. Larvae of Potamocloeon edentatum sp. n. 24, maxilla (ventral view); 25, left half of labrum (dorsal view); 26–27, apices of left and right mandibles before molt to next larval instar. Abbreviations: ds1–ds3, dentisetae.

FIGURES 28–36. Larvae of Potamocloeon edentatum sp. n. 28, 29, tergalii of 1st pair; 30–35, tergalii of 2nd–7th pairs; 36, labium (at left ventral view and musculature, at right dorsal view).

FIGURES 37–44. Larvae of Potamocloeon edentatum sp. n. 37, fore leg (dorsal view); 38, articulation of femur and tibia of middle leg (dorsal view); 39, fragment of fore tarsus (ventral view); 40, fragment of middle tarsus (ventral view); 41–42, claws; 43, exuviae of paraprocts and protogonostyli of male larva; 44, exuviae of 9th and 10th terga.

FIGURES 45–51. Larval legs of Potamocloeon edentatum sp. n. (instead of long hairs, only their bases are shown as small rings). 45, fore femur (dorsal view); 46, middle femur (dorsal view); 47, fore tibia (anterior view); 48, middle tibia (anterior view); 49, hind tibia (anterior view); 50, fore tarsus (dorsal view), 51, middle tarsus (dorsal view).

FIGURES 52–55. Larval abdominal sterna of Potamocloeon edentatum sp. n. 52, halves of abdominal sterna II–VIII; 53, frag- ment of sternum III; 54, fragment of sternum V; 55, fragment of sternum VII.

FIGURES 56–62. Potamocloeon edentatum sp. n. 56, abdominal terga of male imago; 57–59, male imagines; 60, abdominal sterna of male imago; 61–62, female imago (56, 60, holotype).

FIGURES 63–69. Potamocloeon edentatum sp. n. 63, subimaginal exuviae of tibia and tarsus of female fore leg; 64, the same, hind leg; 65, its imaginal hind leg; 66, subimaginal exuviae of mesopleuron; 67, subimaginal exuviae of left half of mesonotum; 68–69, genitals of male imagines (66–68, holotype).

FIGURES 70–72. Potamocloeon edentatum sp. n. 70, subimaginal exuviae of gonostyli; 71, genitals of male imago (gonostylar muscle shown only on right side, gonovectal muscles shown only on left side, gonoducts shown by dotted line); 72, larval protogonostyli with developing subimaginal genitas inside. Abbreviations: gs1–gs3, segments of gonostylus; m.IX-X, areas of anterior attachment of median paraproctal muscles (i.e., muscles going from sternum IX to common base of paraprocts); m.sg, median sterno-styligeral muscle; pgs, protogonostylus; usg, unistyliger.

FIGURES 73–76. Potamocloeon edentatum sp. n. 73–75, eggs; 76, tergalius IV.