Procloeon monilistylus, Kluge, Nikita J., Tiunova, Tatiana M. & Novikova, Eugenia A., 2014

Kluge, Nikita J., Tiunova, Tatiana M. & Novikova, Eugenia A., 2014, A new species, Procloeon monilistylus sp. n. (Ephemeroptera, Baetidae), from the Russian Far East, Zootaxa 3786 (4), pp. 483-491 : 484-490

Procloeon monilistylus sp. n.

( Figs 1–35 )

Cloeon (Centroptilum) sp. 1: Kluge & Novikova 1992: 64 (larva). Cloeon monilistylus: Tiunova 2003: 9 (nomen nudum). Procloeon /g 1 sp.: Kluge 2011: 375.

Material. HOLOTYPE: L-S-I ♂, RUSSIA, Primorskiy Kray (Primorskiy Territory), Spassk region, Hvalynka, river Odarka, 4.VIII.1998, coll. D. Apanaskevich ( ZIN).

PARATYPES: L-S-I♂, reared together with holotype; the same locality, 1 S-I♀ (larval exuviae lost), 3 larvae ( ZIN); Hasan Region, river Sidime (= Narva) near natural reserve Kerdrovaya Pad', VII.1980, coll. N. Kluge: 1 larva ( ZIN); Hasan Region, near Perevoznaya, 21.VI.2013, coll. I. Tiunov: 11 I ♂ ( IBSS). KHABAROVSKIY KRAY (Khabarovsk Territory): Pereyaslavka Region, river Kiya, 2 km lower Petrovichi, 3.VI.1996, coll. T. Tiunova: 1 I ♂ ( ZIN); Nikolaevsk Region, left bank of river Amur near Innokentievka, 6.VII.2000, coll. T. Tiunova: 1 I ♂, 1 S♂ ( ZIN); 5 I ♂,1 S♀ ( IBSS); bassin of river Khor, anabranch Potopilikha, 14.VII.2005, coll. T. Tiunova: 1 I ♂. AMURSKAYA OBLAST' (Amur Province): river Ganukan near Kusatkino, 13.VIII.2003, coll. T. Tiunova: 2 I ♂ ( ZIN); 13 I ♂, 8 I ♀ ( IBSS); river Ignashikha (left tributary of river Amur) near frontier post Ignashino, 28– 29.VIII.2004, coll. T. Tiunova: 1 larva ( IBSS); river Zeya upstream of Mazanovo, 5.VIII.2006, coll. T. Tiunova: 1 I ♂ ( IBSS).

Descriptions. Larva. CUTICULAR COLORATION: Thoracic terga light, with brownish maculae, fore protoptera unicolorous. Legs light, femur with contrasting brown band near apex ( Fig. 22 ). Abdominal terga light, with brown maculae similar on all segments II–IX ( Fig. 17 ). Each abdominal sternum I–VIII colorless, with pair of brownish sublateral maculae; sternum IX brownish. Caudalii light, without dark band.

HYPODERMAL COLORATION: Each abdominal tergum II–IX with pair of brown submedian marking adjacent to posterior margin (as in imago, Fig. 18 ) and visible through blanks located on cuticle at these places ( Fig. 17 ).

SHAPE AND SETATION: Labrum wide, its distal margin concave; setae on distal margin non-branched; outer surface without constant stout setae, with sparsely and irregularly situated thin setae (not shown in Fig. 4 ). Mandibles relatively long, with convex outer margin; on both mandibles incisor and kinetodontium separated beginning from base ( Fig. 5, 6 ). Maxillary palp 3-segmented, with short 2nd segment and long 3rd segment, length of 3rd segment more than twice exceeds length of 2nd segment ( Fig. 7 ). Labial palp with 3rd segment truncate and widened apically ( Fig. 8 ).

Hind protoptera absent; margin of metanotum smooth, without any vestiges of hind protoptera. Fore femur shorter than middle and hind femora; other segments subequal in length on all legs; in paratype male larva proportion of femur/tibia/tarsus/claw on fore leg 90:50:60:35; on middle leg 102:50:60:35; on hind leg 105:50:60:35. Femur with outer side smooth, lacking setae; apex serrate, lacking setae; inner side with sparse, small (7–10 times shorter than femur width), pointed, spine-like setae; on fore leg these setae more densely distributed than on middle and hind legs ( Fig. 22 ). Tibia and tarsus with outer side smooth, lacking setae; inner side with pointed, spine-like setae of moderate size and density (2–6 times shorter than tibia width, with spaces subequal to their length) ( Fig. 22 ). Patella-tibial suture equally developed on all legs. Claw long and slender; with 2 rows of denticles occupying less than 1/3 of claw length; denticles small, very thin, almost seta-like ( Fig. 21 ).

Surface of abdominal terga and sterna with translucent scales in semilunar nests. Tergum I with minute irregular denticles on median part of posterior margin, without posterolateral spines. Terga II–IX with larger and smaller pointed spines on median part of posterior margin. Terga II–VII with pointed posterolateral spines ( Fig. 17 ). Row of spines along lateral margin well-developed on segments VIII and IX; few lateral spines sometimes present on segment VII. Tergum X with long pointed spines on posterior margin ( Fig. 9 ). Sterna I–III or I–IV without spines or denticles on posterior margin. Posterior margins of sterna V–IX with pointed spines smaller than spines on posterior margins of terga. Paraproct with long pointed spines (similar to spines on terga) ( Fig. 9 ). All tergalii I–VII pointed apically; tergalii I–V sharply asymmetric, with prominent proximal-anal lobe ( Figs 10–15 ). Caudalii with posterior margin of each 4th segment darkened, with large spines; in distal part of cercus lateral spines very large, equal to segment length ( Figs 1–3 ).

MALE STRUCTURE: Sibimaginal gonostyli developing under larval cuticle, folded such that 1st segments approximate, 2nd segments directed laterally-caudally and 3rd segments directed caudally ( Fig. 23 ).

Subimago. CUTICULAR COLORATION: Lateral part of mesonotum with brown markings ( Fig. 20 ); mesothoracic anepimeron brown; posterior part of postsubalar sclerite brown ( Fig. 19 ); other subimaginal cuticle colorless.

HYPODERMAL COLORATION: As in imago.

SHAPE AND TEXTURE: On fore leg 1st tarsal segment (shortened) covered by microtrichiae (as tibia and most of rest of body); 2nd–5th segments covered by pointed microlepides. On middle and hind legs, area corresponding to 1st tarsal segment (fused with 2nd segment) covered by microtrichiae (as tibia and most of rest of body); 2nd–5th segments covered by pointed microlepides. Gonostylus with 2nd segment thicker than in imago, without subapical projection and without grooved concavity of inner margin; unlike imago, 3rd (apical) segment attached not ventrally, but apically or dorsally ( Fig. 24 ).

Imago, male. Head and thorax light-yellowish. Turbinate eyes unicolorous, yellow, high, widened apically; facetted surfaces nearly symmetrically-oval ( Figs. 28, 29 ). Medial longitudinal suture of mesonotum convex (as in Fig. 26 ). Fore wings colorless, veins colorless, pterostigma with 3–6 non-branched oblique veins, sometimes some incomplete ( Fig. 16 ). Hind wings absent. Legs light yellowish, unicolorous. In holotype, proportion of femur to tibia to tarsal segments 1st+2nd, 3rd, 4th and 5th on fore leg 120:150:70:60:35:20; on middle and hind leg 110:85:40:14:6:16. On middle and hind legs tarsus with 2 apical thorns: 1st+2nd and 3rd tarsomeres thorn-baring. Abdomen light yellowish, each tergum with pair of submedian brown maculae near posterior margin; terga IV and VII with pair of indistinct sublateral brownish maculae ( Fig. 18 ). Cerci light yellowish, unicolorous.

STRUCTURE OF MALE GENITALS ( Figs 23–25 , 30, 31 ): Styliger with median finger-like process. Shape of gonostylus composite: proximal part of 1st segment sharply projected medially; 2nd segment widened apically, with subapical median projection and grooved concave median margin proximad of this projection; 3rd (apical) segment long, attached on ventral side of 2nd segment ( Fig. 25 ). Penis with unusual 2-stepped shape of median external part ( Figs 30, 31 ). Ventral-proximal margin of penis (hidden by styliger) with pair of sclerotized sublateral thickenings at points of muscles attachment; apices of gonovectes fused with penial bridge, so that gonovectes resemble pair of loops.

Imago, female. Coloration as in male. Eyes large, elevated above head, approximate, with parallel median margins ( Figs 26, 27 ). On fore leg tarsus with 2 apical thorns: 2nd and 3rd tarsomeres thorn-bearing; on middle and hind legs tarsus also with 2 apical thorns: 1st+2nd and 3rd tarsomeres thorn-bearing (as in male).

Egg. Oval, 0.16 mm long. Chorion with even net-like relief with irregular small cells ( Figs 32–35 ).

Dimension. Fore wing length 4–5 mm.

Etymology. The specific epithet is a reference to the appearance of the gonostyli. They appear moniliform because of the presence of a median projection on the 2nd segment.

Diagnosis. The male imago of P. monilistylus differs from all other mayfly species by the shape of the gonostyli.

Besides P. monilistylus , only two Palaearctic species of Procloeon lack hind wings in the adult stage and hind protoptera in the larval stage: P. bifidum Bengtsson 1912 (= P. ornatum Tshernova 1928 ; = P. pseudorufulum Kimmins 1957 ; = P. lychnidense Ikonomov 1962 ) and P. heterophillum Kluge & Novikova 1992 . The larva of P. monilistylus differs from these two species by having a deeply divided incisor and kinetodontium of the mandibles.

Discussion. Originally, the species described here was wrongly attributed not to Procloeon , but to Centroptilum , because it was known only from a single larval specimen lacking tergalii and caudalii ( Kluge & Novikova 1992).

The taxon Procloeon s.l. (or Procloeon /g1, according to the rank-free hierarchical nomenclature) corresponds to the phylogenetic branch 11 in our earlier paper ( Kluge & Novikova 1992: Fig. 11 ) and is characterized by autapomorphies: (1) denticles on outer side of larval cerci are enlarged and transformed to heavy spines in such a manner, that in distal part of cercus each segment bears a single spine as long as the segment; (2) eyes of female imago are enlarged, elongate and elevated, with parallel inner margins. Besides this, Procloeon has characters common with Cloeon s.str.: (3) lateral sides of larval abdominal segments VIII and IX bear denticles; (4) in genitals of the male imago gonovectes are fused by their apices with the penial bridge. All these characters are present in Procloeon monilistylus sp. n. ( Figs 3 , 17 , 23, 26, 27 , 30, 31 ). The taxon Centroptilum is monotypic ( Kluge 2011) and differs from Procloeon by the following characters: (1) larval cerci lack heavy spines; (2) eyes of female imago are small, widely separated and located in the same plane with dorsal surface of head; (3) larval abdominal segments without lateral denticles; (4) gonovectes retain free apices.

The taxon Procloeon /g1 includes a subordinated taxon Pseudocentroptiloides Jacob 1987 , which is characterized by autapomorphies in the larval mouth apparatus and can be treated either as a subgenus of the genus Procloeon , or as a genus in the Procloeon group of genera. Other representatives of Procloeon /g1 constitute a plesiomorphon Procloeon /g2, which in rank-based nomenclature can be treated either as a genus Procloeon , or as a subgenus Procloeon (e.g., Kluge & Novikova 1992); it includes both two-winged species originally placed to the genus Procloeon , and species with hind wings, originally placed to the artificial genus Centroptilum .

Some authors (e.g., Jacob 1991) attribute to the genus Procloeon , besides other species with hind wings, also Cloeon unguiculatum Tshernova 1941 (= Pseudocentroptilum motasi Bogoescu 1947 ; = Centroptilum limnale Braasch & Soldan 1983 ), which is the type species of Pseudocentroptilum Bogoescu 1947 . This species has no characters (1) and (2) and its relationship with true Procloeon is questionable. They also divide the genus Procloeon into two subgenera— Procloeon and Pseudocentroptilum , based on a single character: absence/presence of hind wings. However, absence of hind wings is not enough to prove holophyly of the subgenus Procloeon , because loss of hind wings independently took place in many taxa of Baetidae . Besides the genus Procloeon sensu Jacob 1991 , in many other recently accepted genera of Baetidae (e.g., Pseudocentroptiloides Jacob 1987 , Labiobaetis Novikova & Kluge 1987 , Nigrobaetis Kazlauskas 1987 , Cloeodes Traver 1938 , Paracloeodes Day 1955 , Acentrella Bengtsson 1912 ) hind wings are retained in some species, being lost in others. In many other nonrelated baetid taxa the hind wings also are lost.

Figures

FIGURES 1 – 15. Procloeon monilistylus sp. n., larva. 1 – 3, cercus and two portions of its distal part; 4, labrum; 5, right mandible; 6, left mandible; 7, maxillary palp; 8, labial palp; 9, paraproct and margin of tenth abdominal tergum; 10 – 15, tergalii of pairs I, II, IV, V, VI and VII.

FIGURES 16 – 22. Procloeon monilistylus sp. n. 16, wing; 17, cuticle of larval terga, spread on slide (hypodermal pigmentation not shown); 18, abdominal terga of male imago, spread on slide; 19, cuticle of subimaginal postsubalar sclerite and lateropostnotal crest; 20, cuticle of subimaginal mesonotum, spread on slide; 21, larval claw; 22, larval fore leg.

FIGURES 23 – 29. Procloeon monilistylus sp. n. 23, posterior margin of male larval abdominal sternum IX and subimaginal genitals developing under larval cuticle (right gonostylar muscle shown by interrupted lines); 24, genitals of male subimago, ventral view (imaginal gonostyli and gonostyli pedestals developing under subimaginal cuticle, shown by interrupted lines); 25, male imaginal abdominal sternum IX with styliger and gonostyli (unpaired sterno-styligeral muscle, pair of penial muscles and right gonostylar muscle shown by interrupted lines); 26, had and thorax of female imago, frontal view; 27, head of female imago, dorsal view; 28, head of male imago, dorsal view; head of male imago, lateral view.

FIGURES 30 – 31. Procloeon monilistylus sp. n., styliger and penis of male imago, ventral view (penis dotted, its hidden part shown by interrupted lines). 30, specimen from Ganukan, in projected condition (muscles not shown); 31, specimen from Kyia, penis in re 4 tracted condition (penial muscles and right gonostylar muscle shown by interrupted lines).

FIGURES 32 – 35. Procloeon monilistylus sp. n., eggs and enlarged micropilar area.