Procloeon (Monilistylus), Kluge, 2020

Kluge, Nikita J., 2020, New subgenus Monilistylus subgen. n. and a new species Procloeon (Monilistylus) ornatipennis sp. n. (Ephemeroptera: Baetidae: Procloeon), Zootaxa 4742 (3), pp. 573-587 : 578-579

Monilistylus subgen. n.

( Figs 1–54 )

Type species: Procloeon monilistylus Kluge, Tiunova & Novikova 2014 .

Autapomorphies of Monilistylus.

(1) In male imago, sterno-styligeral muscle (initially unpaired) has enlarged paired lateral portions, which are attached to the bases of unistyligers ( Figs 51 , 53 ), so that each lateral portion can serve as adductor of the unistyliger.

In our previous paper (Kluge et al. 2014) the lateral portions of the sterno-styligeral muscle were wrongly interpreted as «penial muscles» (Kluge et al. 2014: legend to fig. 25) or as parts of the «penial muscles» (ibid: legend to fig. 31). This error was caused by the fact that in P. (M.) monilistylus the lateral portions of the sterno-styligeral muscle run parallel to the gonovectal (penial) muscles and completely overlap them in ventral view, so that these two pairs of muscles look as one pair (compare left and right halves of Fig. 52 ). In the new species, P. (M.) ornatipennis sp. n., the lateral portions of the sterno-styligeral muscle are divergent caudally ( Fig 51 ), while the gonovectal (penial) muscles are convergent caudally ( Fig. 50 ), so that in ventral view these two pairs of muscles cross one another, being well distinguishable ( Fig. 49 ).

Initially for Ephemeroptera , the sterno-styligeral muscle is unpaired and serves for rotation of the unpaired styliger as a whole to the ventral direction; when this muscle is contracted, the styliger becomes directed perpendicular to the body and the penis becomes protracted ( Kluge 2003: figs 3–7; 2004: figs 10–11). In Baetidae , the styliger is divided to a pair of unistyligers separated by a deep incision, and the sterno-styligeral muscle is attached to the integument of this incision ( Kluge & Novikova 2011: fig. 3); as a result of this, contraction of the sterno-styligeral muscle leads not to a rotation of the styliger ventrally, but to inclining the unistyligers toward one another. Primitively for Baetidae , the sterno-styligeral muscle is wide and strong, the place of its attachment between unistyligers is sclerotized, and its lateral parts touch the bases of unistyligers ( Kluge 2018: fig. 46). In many baetid taxa, the median sclerite between unistyligers is lost; the sterno-styligeral muscle is often weak and unable to move the unistyligers; in selected taxa this muscle is completely lost (e.g., in Labiobaetini Kluge & Novikova 2016 and Rhodobaetis Jacob 2003 ). In Monilistylus, the sterno-styligeral muscle evolved in opposite direction, so that its lateral portions become strong and look as paired muscles.

(2) The second segment of the gonostylus has a composite shape: its proximal 2/3 has a groove on its concave median side; the distal 1/3 has no groove and forms a blunt angle with the grooved proximal portion ( Figs 49 , 53 ).

Characters of Monilistylus of unclear phylogenetic status.

(3) Mandibles of the « Centroptilum - type »: the kinetodontium is deeply separated from the incisor and rotated perpendicular to the plane of the mandible, so that its denticles hide one another in dorsal or ventral view; the left prostheca is bifurcate and rotated in the same manner ( Figs 4 , 18–25 ). Among Procloeon /g1, such « Centroptilum - type » of mandibles, besides Monilistylus, occurs in Pseudocentroptiloides and Securiops as well; it is also present in some other baetid taxa (Kluge, in press). In other taxa of Procloeon /g1, the mandibles are of the « Baetis - type »: the kinetodontium is fused with the incisor; the left prostheca is wide, terminated by 3–6 blunt, more distal denticles and 2–4 pointed, more proximal denticles; all denticles of incisor, kinetodontium, prostheca and mola are visible in one view.

(4) Larval femur without stout apical setae on outer margin ( Figs 30–31 ) (in contrast to Oculogaster and various taxa not belonging to Cloeon /fg1, which have 2 stout apical setae).

Plesiomorphies of Monilistylus. In contrast to Oculogaster , pterostigma with several cross veins ( Fig. 44 ), eggs with sculptured chorion (known for P. (M.) monilistylus only). In contrast to Pseudocentroptiloides , the maxillae are narrowed distally ( Fig. 17 ), the labrum is not deeply emarginated ( Fig. 16 ). In contrast to Pseudocentroptiloides and Securiops , the glossae are not much longer than the paraglossae ( Figs 28–29 ).

Distribution. Oriental Region and south-east of Palaearctic.

Species composition. Two species: Procloeon (Monilistylus) monilistylus Kluge, Tiunova & Novikova 2014 (south of Russian Far East) and Procloeon (Monilistylus) ornatipennis sp. n. ( Indonesia).

Figures

FIGURES 1–8. Larval exuviae. 1–2, Procloeon (Monilistylus) monilistylus: 1, right half of pro- and mesonotum; 2, thoracic sterna, pleura, metanotum, abdominal sterna and terga. 3–8, Procloeon (Monilistylus) ornatipennis sp. n.: 3, right half of pro- and mesonotum; 4, head; 5, thoracic sterna, pleura, metanotum and two legs; 6, abdominal sterna and terga (with caudalii of holotype); 7–8, caudalii of holotype, enlarged.

FIGURES 9–25. Details of larvae. 9–23, Procloeon (Monilistylus) ornatipennis sp. n.: 9–15, tergalii I–VII (holotype); 16, labrum; 17, maxilla (dorsal view); 18, right mandible; 19, its kinetodontium rotated after pressure of slide; 20, left mandible; 21–23, its incisor, kinetodontium and prostheca rotated after pressure of slide. 24–25, Procloeon (Monilistylus) monilistylus, kinetodontium and prostheca rotated after pressure of slide.

FIGURES 26–29. Procloeon (Monilistylus) ornatipennis sp. n., exuviae of labium: 26, general view with focus on ventral side; 27, labial palp with focus on dorsal side; 28, glossa and paraglossa with focus on ventral side; 29, the same with focus on dorsal side (26, holotype).

FIGURES 30–32. Procloeon (Monilistylus) ornatipennis sp. n., legs: 30, foreleg in anterior view (holotype); 31, base of tibia in anterior view; 32, claw.

FIGURES 33–38. Procloeon (Monilistylus) ornatipennis sp. n.: 33, larval exuviae of posterior margin of 9th abdominal sternum with protogonostyli; 34, subimaginal tissues with gonostyli, extracted from it; 35, exuviae of paraprocts and protogonostyli of another specimen; 36, exuviae of 5th abdominal sternum (Figs 33–36 under the same magnification); 37,middle of posterior margin of 9th abdominal tergum; 38, portion of mesonotum (magnification as in Fig. 37).Abbreviations: gs1, gs2, gs3, segments of gonostylus; m.gs, gonostylar muscle; m.gv, gonovectal (penial) muscle; m.s., lateral portion of styligeral muscle.

FIGURES 39–46. Procloeon (Monilistylus) ornatipennis sp. n.: 39–40, male imagines; 41, male imaginal genitals; 42, exuviae of right half of subimaginal mesonotum; 43, exuviae of left half of subimaginal mesopleuron; 44, wing; 45, abdominal terga II–VII; 46, tibia and tarsus of middle leg (41–43 and 45–46, holotype).

FIGURES 47–51. Procloeon (Monilistylus) ornatipennis sp. n. (holotype): 47, median projection of penis; 48, exuviae of subimaginal gonostyli; 49, genitals with all visible muscles (muscles and hidden parts of penis shown by interrupted lines); 50, the same with penis, its muscles and gonoducts (shown by dotted line); 51, the same with muscles of styliger (penis not shown). Abbreviations: gs1, gs2, gs3, segments of gonostylus; m.IX-X, area of attachment of intersegmental paraproctal muscle; m.gs, gonostylar muscle; m.gv, gonovectal (penial) muscle; m.s., lateral portion of styligeral muscle; usg, unistyliger.

FIGURES 52–54. Procloeon (Monilistylus) monilistylus: 52–53, genital of male imago (corrected from Kluge et al. 2014); 54, exuviae of subimaginal gonostyli. Abbreviations: gs1, gs2, gs3, segments of gonostylus; m.gs, gonostylar muscle; m.gv, gonovectal (penial) muscle; m.s., median and lateral portions of styligeral muscle; usg, unistyliger.