Cheleocloeon psammonella, 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 : 341-349

publication ID	https://doi.org/10.11646/zootaxa.5660.3.2
publication LSID	lsid:zoobank.org:pub:DB5BCD88-5794-4BA6-AABF-1286D1C1EE52
persistent identifier	https://treatment.plazi.org/id/DA3E8786-F50C-1641-2DCC-F912FECF878B
treatment provided by	Plazi
scientific name	Cheleocloeon psammonella
status	sp. nov.

Treatment

Cheleocloeon psammonella sp. nov.

( Figs 50–82 View FIGURES 50–55 View FIGURES 56–60 View FIGURES 61–63 View FIGURES 64–66 View FIGURES 67–72 View FIGURES 73–78 View FIGURES 79–82 )

Material. Holotype: L-S/I ♂ {specimen [X] (13) 2017}, TANZANIA, Iringa Region, Uszungwa Mountains, river Msosa (tributary of Great Ruaha ), Msosa Camp (9 km S Mbuyuni), 7°33′S, 36°32′E, 7.VIII.2017, coll. N. Kluge and L. Sheyko. GoogleMaps

Etymology. The feminine noun psammonella repeats the genus-group name Psammonella Glazaczow (in Jacob & Glazaczow) 1987, which was derived from Greek ψαμμη (sand) referring to the preferred larval substratum. The name refers to the convergent similarity between this species of Cheleocloeon and the subgenus Psammonella , belonging to Procloeon Bengtsson 1915 .

Descriptions

Larva. CUTICULAR COLORATION: Cuticle with brown ornament on colorless background. Dorsal eyes (of mature male larva) brown, occipit between them partly brown; other parts of head cuticle colorless ( Fig. 52 View FIGURES 50–55 ). Pronotum and mesonotum with brown and colorless areas; cuticle of fore protoptera light ocher-brownish with incomplete brown stripes along some convex veins and with colorless stripes along distal parts of concave veins ( Fig. 51 View FIGURES 50–55 ). Metanotum brown; metapleura partly brown ( Fig. 54 View FIGURES 50–55 ), other thoracic pleura and sterna colorless. Femora colorless, with diffusive brown longitudinal macula in distal part; tibiae and tarsi nearly colorless, diffusively darkened on outer side ( Figs 53–55 View FIGURES 50–55 ). Abdominal terga with composite ornament of brown and colorless areas; terga I and VI darkest; tergum III darker than tergum II; anterior and posterior margins of terga bordered by dark brown; sterna colorless; segment X (tergum and paraprocts) light ( Fig. 50 View FIGURES 50–55 ). Cerci uniformly light brownish; paracercus lighter, with posterior margins of segments darkened with brown ( Fig. 50 View FIGURES 50–55 , 72 View FIGURES 67–72 ).

HYPODERMAL COLORATION. Unknown.

SHAPE AND SETATION: Labrum with anterior margin concave ( Fig. 56 View FIGURES 56–60 ). Incisors of mandibles wide and short, with most distal denticles shortest and bent ventrally ( Figs 57–58 View FIGURES 56–60 ).

Maxilla of peculiar structure, different from that of other Cheleocloeon (compare: Kluge 2016: fig. 2) ( Figs 59 View FIGURES 56–60 , 61–63 View FIGURES 61–63 ): Maxillary canines fused together forming short and flat apical plate with smooth outer margin; this apical plate borders bases of medio-ventral setal row from distal and ventral sides. Medio-ventral setal row terminates close to the apical plate; its 4 most distal setae are flattened and widened distally, much longer than the apical plate and arched backward from it; several previous setae are also arched at the same direction ( Figs 61–62 View FIGURES 61–63 ). Mediodorsal setal row contains 3 distinguishable dentisetae ( Fig. 61 View FIGURES 61–63 ).

Labium of peculiar structure, different from that of other Cheleocloeon (compare: Kluge 2016: figs 4–5) ( Figs 60 View FIGURES 56–60 , 64–65 View FIGURES 64–66 ). Glossae shortened and blunt apically. Paraglossae blunt apically, with enlarged number of long setae at apex. Disto-median projection of 2nd segment of labial palp (characteristic for Cheleocloeon ) sharply projected, apically narrowly rounded, but not pointed ( Fig. 66 View FIGURES 64–66 ).

Legs slender. Claw long and slender, slightly arched, completely lacking denticles ( Fig. 55 View FIGURES 50–55 ).

Hind protoptera absent in male ( Fig. 54 View FIGURES 50–55 ) (the same should be in female).

Abdominal terga I–X with dense scales in wide sockets ( Fig. 70 View FIGURES 67–72 ). Posterior margin of tergum I with few irregular denticles; posterior margin of terga II–X with regular row of dark brown pointed denticles alternated with scales ( Fig. 70 View FIGURES 67–72 ). Posterior margins of abdominal sterna I–IV smooth; posterior margins of sterna V–IX with regular row of colorless triangular denticles, smaller than denticles on terga, without scales between them. Paraproct with pointed denticles ( Fig. 69 View FIGURES 67–72 ). All tergalii I–VII narrow and widest in distal half; tergalius I narrowest, shorter than next ones ( Figs 73–78 View FIGURES 73–78 ). Cerci without enlarged denticles on lateral sides; paracercus with several pointed enlarged denticles on dorsal side of posterior margin of each 4th segment ( Fig. 72 View FIGURES 67–72 ). Distal part of cercus with longitudinal row secondary swimming setae on lateral side (besides primary swimming setae on medial side) ( Fig. 71 View FIGURES 67–72 ).

Pose of subimaginal gonostyli under larval cuticle (retained in examined winged specimen). « Cloeon - type » ( Fig. 79 View FIGURES 79–82 ), as in other Cheleocloeon (see Kluge 2016: character 22 on p. 144).

Subimago. CUTICULAR COLORATION. Mesonotum light brownish, with darker brown areas ( Fig. 82 View FIGURES 79–82 ).

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

Imago, male (enclosed in subimaginal cuticle) ( Fig. 81 View FIGURES 79–82 ). Head ochre-brown. Turbinate eyes yellow. Thorax brown, equally dark on dorsal, ventral and lateral sides. Hind wings absent. Legs uniformly pale ochre. Abdominal terga light brownish-ochre, with poorly expressed reddish markings along median line, on posterior margins of terga and on sides of terga III and V; sterna uniformly light ochre. Shape of gonostyli unknown (not spread after molt from larva); gonovectes dark brown, structure of gonovectes typical for Cheleocloeon ( Fig. 79–80 View FIGURES 79–82 ). Cerci uniformly pale ochre.

Imago, female. Unknown.

Egg. Unknown.

Dimension. Fore wing length (and body length) about 3 mm.

Distribution. Known from one place in Tanzania.

Systematic position. The new species Ch. psammonella sp. nov. undoubtedly belongs to Cheleocloeon . Its shape of labial palp is typical for Cheleocloeon , i.e. with disto-median projection of the 2nd segment greatly projected medially and bent backward ( Fig. 60 View FIGURES 56–60 ); male imaginal gonovectes, which are developed in the specimen examined ( Fig. 80 View FIGURES 79–82 ), have structure characteristic for Cheleocloeon .

Comparison. Larva of Cheleocloeon psammonella sp. nov. differs from all other species of Cheleocloeon by the following features of the mouthparts’ structure: anterior margin of labrum is concave ( Fig. 56 View FIGURES 56–60 ) (rather than convex with median concavity in other species— Fig. 8 View FIGURES 8–14 ); maxillary canines and setae of the medio-ventral row are modified forming a scraper ( Figs 62–63 View FIGURES 61–63 ) (rather than pointed maxillary canines and slender setae in other species— Fig.11 View FIGURES 8–14 ); glossae and paraglossae are more blunt, and glossae are shorter than in all other species of Cheleocloeon ( Figs 60 View FIGURES 56–60 , 64–65 View FIGURES 64–66 ). These mouthparts modifications in Cheleocloeon psammonella sp. nov. resemble the modifications characteristic for the taxa Pseudocentroptiloides Jacob (in Jacob & Glazaczow) 1987 and Psammonella Glazaczow (in Jacob & Glazaczow) 1987, which belong to the genus Procloeon Bengtsson 1915 . Other representatives of Procloeon have the same structure of labrum, maxillae, glossae and paraglossae, as representatives of Cheleocloeon other than Ch. psammonella sp. nov.

Larva of Ch. psammonella sp. nov. also differs from all other species of Cheleocloeon by longer and slender legs with especially long and slender claws lacking denticles ( Fig. 55 View FIGURES 50–55 ) (in other species at least a few minute denticles are present—see Fig. 18 View FIGURES 18–22 and Kluge 2016: figs 19–29).

Such leg structure is also characteristic for Pseudocentroptiloides and Psammonella. Probably, both the leg structure and the mouthparts’ structure are adaptations for inhabitancy on sand ground, convergently evolved in these taxa. The single larva of Ch. psammonella sp. nov. was collected in river Msosa, where most bottom consists of pure sand.