Cheleocloeon acutipalpum, Kluge, 2025

Kluge, Nikita J., 2025, Two new species of the genus Cheleocloeon Wuillot & Gillies 1993 (Ephemeroptera: Baetidae) from Tanzania and corrections to the generic diagnosis, Zootaxa 5660 (3), pp. 330-350 : 332-341

Cheleocloeon acutipalpum sp. nov.

( Figs 1–49 )

Material. Holotype: L-S-I ♂ {specimen [XXXVIII] (15) 2016} TANZANIA, Tanga Region, Amani, Usambara Mountains, river Sigi , 5°06’S, 38°38’E, 1.IX.2016, coll. N. Kluge & L. Sheyko. Paratypes: TANZANIA: the same locality and collectors, 19.VIII–2. IX.2016: 1 L-S-I ♂ , 1 L-S ♂, 11 larvae; Mbeya Region, Matema, Livingstone Mountains, river Mwalalo (tributary of Lake Nyasa ), 9°29′S, 34°02′E, 6–14.VIII.2016, coll. N. Kluge & L. Sheyko: 4 L-S-I ♂ , 2 L-S ♂, 5 L-S-I ♀, 2 L-S ♀, 7 larvae; Morogoro Region, Uluguru Mountains : river Morogoro in Morogoro, 31.VII.2017, coll. N. Kluge & L. Sheyko: 4 larvae ; basin of river Ruvu near Kinole , 6°54′S, 37°45′E, 27–30.VII.2017, coll. N. Kluge & L. Sheyko: 2 L-S-I ♀, 2 larvae .

Etymology. The adjective acutipalpum refers to acute apex of the disto-median projection of 2nd segment of labial palp.

Descriptions

Larva. CUTICULAR COLORATION: Cuticle with contrasting ornament of brown and colorless areas. Frons close to frontal suture darkened, vertex darkened with composite blanks corresponding to attachments of mandibularcranial adductors ( Fig. 2 ). Pronotum and mesonotum with composite ornament of brown and colorless areas; cuticle of fore protoptera brown, distally lighter, with darker brown stripes along convex longitudinal veins and colorless stripes along concave longitudinal veins ( Figs 3, 6 ). Metanotum brown with pair of transverse blanks; hind protoptera of male brown, distally lighter ( Figs 4–5 ). Thoracic pleura brown with colorless blanks, thoracic sterna colorless ( Fig. 5 ). Femora colorless, with or without diffusive brown longitudinal macula in distal part; tibiae and tarsi either nearly colorless, or diffusively darkened on outer side, or brown with colorless patella-tibial suture ( Figs 5 , 15–17 ). Abdominal terga with composite ornament of brown and colorless areas; terga I, III, VI and IX darker than neighboring ones ( Figs 1, 7 ). Sterna I–VIII mostly colorless; in posterior part of abdomen, anterior margin of each sternum more or less darkened with brown; sternum IX darkened with brown. Caudalii often darkest just distad of middle and at apex, with lighter area between these dark areas (Figs 1,7).

HYPODERMAL COLORATION. Either not expressed, or abdominal terga with reddish or brown median and lateral maculae as in imago ( Fig. 23 ).

SHAPE AND SETATION: Labrum with anterior margin convex, with median incision ( Fig. 8 ). Mandibles— Figs 9–10 . Maxillae non-modified ( Fig. 11 ). Glossae and paraglossae non-modified ( Figs 12–13 ). Disto-median projection of 2nd segment of labial palp (characteristic for Cheleocloeon ) sharply projected, apically pointed ( Fig. 14 ).

Legs slender ( Figs 15–17 ). Claw with pair of longitudinal rows of minute denticles near base, continued by pair of longitudinal rows of few (2–3) wide, very short, truncated, colorless denticles in proximal 1/3 of claw ( Fig. 18 ).

Male larva with hind protoptera ( Fig. 4 ); female larva with vestiges of hind protoptera rather wide and projected posteriad of posterior margin of metanotum ( Fig. 5 ).

Abdominal terga I–X with dense scales in wide sockets; narrower and longer scales located near posterior margin, some attached on posterior margin between denticles ( Fig. 21 ). Posterior margin of tergum I with smaller denticles; posterior margin of terga II–X bordered by dark brown band and bear regular row of dark brown pointed denticles ( Fig. 21 ). Posterior margins of abdominal sterna I–IV smooth; posterior margins of sterna V–IX with regular row of denticles, smaller than denticles on terga, without scales between them. Paraproct with pointed denticles ( Fig. 20 ). All tergalii I–VII not wide and widest in distal half; tergalius I narrowest, as long as next ones ( Figs 24–30 ). Lateral side of each cercus and dorsal side of paracercus with several pointed denticles on posterior margin of each 4th segment ( Fig. 22 ). Distal part of cercus with longitudinal row of secondary swimming setae on lateral side (besides primary swimming setae on medial side) (as in Fig. 71 ).

Pose of subimaginal gonostyli under larval cuticle. « Cloeon - type » (as in Fig. 79 ), as in other Cheleocloeon (see Kluge 2016: character 22 on p. 144).

Subimago. CUTICULAR COLORATION. Head colorless. Pronotum light brown with colorless blanks. Mesonotum very light brownish, nearly colorless, with contrasting dark brown anterior part of lateroparapsidal suture, antelateroparapsidal suture, prelateroscutum and parascutellum ( Fig. 46 ). Thoracic pleura and sterna with contrasting dark brown, light brownish and colorless areas ( Fig. 45 ). Legs colorless. Abdominal terga and sterna light brownish, each tergum with pair of darker sublateral spots. Cerci colorless.

TEXTURE. All tarsal segments of all legs covered with pointed microlepides.

Imago, male ( Figs 31–37 ). Head brown. Turbinate eyes nearly cylindrical, slightly widened apically; stem ochre; facetted surface orange, bordered by narrow contrasting dark brown ring. Thorax uniformly brown on dorsal, lateral and ventral sides. Fore leg with femur brown or ochre-brownish, tibia and tarsus lighter; middle and hind legs either uniformly light ochre ( Figs 33–34 ), or with brownish spot near apex of femur ( Fig. 37 ). Middle and hind legs with apical spine of 1st+2nd and 3rd tarsal segments. Fore wing colorless, with veins light ochre, base proximad of costal brace with brown; pterostigma with several simple, oblique, incomplete veins. Hind wing present, narrow, with hooked costal projection ( Fig. 35 ). Abdominal terga from ochre to dark brown, with darker reddish unpaired and paired maculae ( Fig. 31–32 ). Abdominal sterna ochre. Cerci uniformly pale ochre.

Genital structure as characteristic for Cheleocloeon (see Kluge 2016), with following peculiarities ( Figs 38–42 ): Unpaired sclerite between unistyligers absent. Unistyligers with distal margin widened medially to form a pair of projections directed toward one another ( Figs 38, 40, 42 ). 1st segment of gonostylus basally on median side either with well outlined sclerotized concave area ( Figs 38, 40 ), or without it ( Fig. 42 ).

Imago, female ( Fig. 44 ). Head and thorax lighter than in male, brownish-ochre. Abdominal terga either uniformly colored, or with reddish maculae as in male. Hind wings absent. Fore leg with apical spines on 2nd and 3rd tarsal segments. Middle and hind legs as in male.

Egg. Oval; chorion with even and regular net-like relief ( Figs 48–49 ).

Dimension. Fore wing length (and approximated body length) 5 mm.

Distribution. Known from Tanzania: Livingstone Mountains (near Matema), Uluguru Mountains, Usambara Mountains.

Comparison. By the pointed projection of 2nd segment of labial palp ( Fig. 14 ), larva of Ch. acutipalpum sp. nov. resembles Ch. yolandae Wuillot (in Wuillot & Gillies) 1993, Ch. carinatum Wuillot (in Wuillot & Gillies) 1993 and Ch. littorale McCafferty 2001 ; among them, Ch. yolandae and Ch. carinatum differ from other species of Cheleocloeon by lacking hind wings in both sexes. Larva of Ch. acutipalpum sp. nov. well differs from larvae of Ch. yolandae and Ch. carinatum by tergalius of the 1st pair, which is not longer than others ( Fig. 24 ).

Ch. littorale was described as larvae from Lake Nyasa, i.e. in the same area as Ch. acutipalpum sp. nov. According to the original description, larva of Ch. littorale has «Claws ... with inner marginal row of 12–14 ... denticles ... extending from near the base of the claw to approximately two-thirds length of claw» ( McCafferty 2001: 66 and Fig. 7 ). In contrast to this, Ch. acutipalpum sp. nov. has very small denticles only on the proximal part of claw ( Fig. 18 ). Projection of 2nd segment of labial palp is pointed also in the undescribed species from Uganda reported as « Cheleocloeon sp. 3 » ( Kluge 2016); this species differs from others by unusually stout legs and peculiar shape of right prostheca.

Male imago of Ch. acutipalpum sp. nov. differs from other species by prominent median projections of unistyligers ( Figs 38, 40, 42 ).

Comment. A part of material on the new species Ch. acutipalpum sp. nov. was collected in the Upper Sigi River in Usambara Mountains, in the place from which the species originally named Cheleocloeon sigiense Gillies 2001 was described. As shown by Kluge (2016) and Kluge et al. (2018), this species does not belong to Cheleocloeon , but belongs to the genus Susua in Protopatellata. The new species Ch. acutipalpum sp. nov. differs from Susua sigiense ( Gillies 2001) by many characters at larval and winged stages, so that M.T. Gillies could not confuse these two species. The species described here as Ch. acutipalpum sp. nov., was not reported under any name in the list of mayfly species from the Upper Sigi River, where Susua sigiense was reported as « Dabulamanzia sp. nov. » ( Gillies 1999).

Figures

FIGURES 1–7. Cheleocloeon acutipalpum sp. nov.: larvalexuviae. 1–4, abdomen,head, pronotumwith mesonotum, metanotum of male specimen from Matema; 5, thoracic pleura with legs and half of metanotum of female specimen from Matema; 6–7, pronotum with mesonotum and abdomen of male specimen from Amani (holotype).

FIGURES 8–14. Cheleocloeon acutipalpum sp. nov.: larval exuviae. 8, labrum; 9–10, left and right mandibles; 11, maxilla; 12–13, labium with focus on dorsal and ventral sides; 14, enlarged fragment of labial palp.

FIGURES 15–17. Cheleocloeon acutipalpum sp. nov.: larval exuviae of legs. 15, fore leg; 16, middle leg; 17, hind leg.

FIGURES 18–22. Cheleocloeon acutipalpum sp. nov.: larval exuviae. 18, claw; 19, fragment of fore femur; 20, abdominal sternum IX and paraprocts of male; 21, abdominal tergum III; 22, fragment of caudalii (18, 21, holotype).

FIGURES 23–30. Cheleocloeon acutipalpum sp. nov. 23, last instar female larva just after molt, with colorless cuticle, to show hypodermal coloration; 24–30, tergalii of I–VII pairs.

FIGURES 31–37. Cheleocloeon acutipalpum sp. nov.: male imagines. 31, dorsal view; 32, abdominal terga and sterna; 33–34, lateral view; 35, hind wing; 36–37, fore and hind legs (34–37, holotype).

FIGURES 38–43. Cheleocloeon acutipalpum sp. nov. 38–40, 42, male imaginal genitalia, ventral view; 41, the same, with focus on gonovectes; 43, exuviae of subimaginal gonostyli (38–39, holotype).

FIGURES 44–49. Cheleocloeon acutipalpum sp. nov. 44, female imago; 45–47, subimaginal exuviae (45, mesopleuron; 46, half of mesonotum; 47, abdomen); 48–49, eggs (46, holotype).

FIGURES 67–72. Cheleocloeon psammonella sp. nov., larval exuviae (holotype). 67, abdominal sternum and tergum IX; 68, tergum X; 69, paraproct; 70, part of tergum VI; 71, distal part of cercus; 72, middle part of cerci and paracercus.

FIGURES 79–82. Cheleocloeon psammonella sp. nov., (holotype). 79, genitalia of male subimago with gonostyli non-spread and retaining folded condition as if being under larval cuticle; 80, right gonovectis and its muscle; 81, head and thorax of male subimago; 82, subimaginal exuviae of right half of mesonotum.