Mesorthocladius, Saether, Ole A., 2005

Saether, Ole A., 2005, A new subgenus and new species of Orthocladius van der Wulp, with a phylogenetic evaluation of the validity of the subgenera of the genus (Diptera: Chironomidae), Zootaxa 974, pp. 1-56 : 26-29

Orthocladius subgen. Mesorthocladius new subgenus

Orthocladius subgen. Rheorthocladius Thienemann, 1944 pro parte, not Thienemann 1935: 235. Orthocladius subgen. Euorthocladius Brundin 1947 , pro parte, not Thienemann 1935: 201. Orthocladius subgen. Orthocladius Goetghebuer, 1932 , not v. d. Wulp 1874: 132.

Type species

Orthocladius (Mesorthocladius) frigidus Kieffer.

Etymology

From Greek, mesos, middle, and Orthocladius , a genus of Orthocladiinae, referring to the phylogenetic position of the subgenus.

Diagnostic characters

The male imagines are separable from those of other subgenera by a combination of characters: collar­like superior volsella; inferior volsella with ventral part not extended below dorsal part; anal point robust with rounded apex or broadly triangular ( O. nimidens ); eyes extended dorsomedially, male­like or when female­like ( O. rousellae ) scutellars multiserial, antepronotals numerous (9–27) and crista dorsalis prominent; scutellars usually multiserial, when uniserial to biserial eyes not female­like and anal point broadly triangular or anal lobe strongly projecting and sensilla chaetica present on both mid and hind leg; anal lobe of wing usually strongly projecting. Tergite IX of female divided, seminal capsule pear­shaped with apical wart or rugulosity, or small, rounded and bare; when small rounded and bare, margins of tergite IX relatively poorly delimited; spermathecal ducts meandering or with one or more loops. Pupae (except O. lamellatus ) with thoracic horn stalked, long, filamentous and smooth or robust with tapered apex and covered with points; when spinous anal lobe with fine sclerotised lateral threads and frontal warts strong and some dorsocentrals spine­like. Orthocladius lamellatus differs from species of the nominal subgenus except O. (O.) chuzesextus Sasa by having pedes spurii B absent on segments II and III, no apical or lateral spines on anal lobe, and median point band on tergites III and IV fused with posterior band. From O. (O.) chuzesextus it differs by its larger size (total length 4.1–5.4 mm, anal macrosetae 225–278 µm long versus 3.0– 3.6 mm, anal macrosetae 184–223 µm long). The larva differs from that of other species of the genus by lacking seta interna of the mandible or when seta interna present, the mentum has 15 or 17 teeth and the premandible is bifid; labral lamellae sometimes present; premandible often bifid.

Imago

Moderately large species, wing length 1.7–3.4 mm. Thorax with brown to blackish brown vittae and other markings and with the ground colour varying from pale to nearly as dark as markings.

Eye bare, reniform, with small or no dorsomedian elongation, occasionally femalelike.

Antenna with 13 flagellomeres in male, 5 in female; male antenna fully plumed; groove beginning on flagellomere 4 or 5; sensilla chaetica present on flagellomere 2, 3 and 13; apex without straight apical seta in male, with in female; AR 1.0–2.1. Palpomeres long, normal; palpomere 3 with 2–3 short lanceolate sensilla clavata. Temporals numerous. Tentorium and stipes normally developed. Cibarial pump with anterior margin deeply concave, cornua moderately to strongly developed. Clypeus with several setae .

Antepronotal lobes with several to numerous lateral antepronotals. Acrostichals starting close to antepronotum, dorsocentrals uniserial to occasionally biserial, few to many prealars, supraalars absent or occasionally present. Scutellum with setae usually transversely bi­ multiserial, occasionally uniserial.

Wing membrane with fine punctation; anal lobe well developed, moderately to strongly projecting; costa not to clearly extended; R2+3 running in the middle between R1 and R4+5; R4+5 and costa ending distal to end of M3+4; VR 1.00–1.12; Cu1 straight to slightly curved, occasionally slightly sinuous apically; postcubitus ending far distal to cubital fork, anal vein ending distal to cubital fork. Brachiolum with 1 seta, R with a few setae ; R1 occasionally with 1 seta, R4+5 of male bare or occasionally with 1 non­marginal seta, in female R1 and R4+5 with setae ; other veins bare. Squama with 17–37 setae . Sensilla campaniformia about 13–14 basally on brachiolum, about 8–10 apically on brachiolum, three below setae on brachiolum; one present basally on subcosta, and one basally on R1 or on RM.

Front leg ratio 0.62–0.72. Tibial spurs and hind tibial comb normal. Tarsal pseudospurs present on ta1 of mid and hind legs, usually on ta2 of mid leg and often on ta2 of hind leg. Pulvilli absent. Sensilla chaetica 0–21 on ta1 of mid leg, 0–16 on hind leg in male; 0–22 on ta1 of each middle and hind leg in female.

Tergites with scattered setae without a distinct pattern. Sternites with median and lateral setae .

Male anal point usually robust, partly parallel­sided with rounded apex and short, stiff lateral setae often directed laterally or even anteriorly; occasionally ( O. nimidens ) anal point broadly triangular and pointed. None to few setae at base on tergite IX; laterosternite IX with several setae . Sternapodeme slightly curved, oral projections well developed. Phallapodeme hooked apically, aedeagal lobe well developed. Virga present and consisting of several small teeth or of cluster of spines or absent. Gonocoxite well developed; superior volsella collar­like or absent; inferior volsella well developed with weak ventral part not extended below dorsal part. Gonostylus with weak to prominent rounded preapical crista dorsalis, megaseta normal.

Female genitalia with evenly curved gonocoxapodemes meeting or indicated anterior of vagina. Gonocoxite well developed, with numerous setae . Tergite IX strongly divided with several setae . Segment X normal. Postgenital plate weak, indistinct, bluntly triangular. Cercus large. Gonapophysis VIII divided into large, brush­like ventrolateral lobe covering part of nearly equally large dorsomesal lobe with or without oral rounded projection. Rami indistinct, barely sclerotised. Apodeme of apodeme lobe distinct. Coxosternapodeme strong laterally, moderately strong to weak and indistinct medially, evenly curved, but sometimes with anterior projection or bend. Seminal capsules small and rounded to pear­shaped, sometimes with apical rugulosity or distinct apical wart; darkly sclerotised for most of their length; with or without neck. Spermathecal ducts slightly meandering, with small loop, or very long with several loops; equally wide throughout; with separate openings. Labia bare.

Pupa

Moderately large pupae, 4.4–6.5 mm long. Exuviae pale greyish brown to pale brown with brown to blackish brown apophyses. Frontal warts prominent, weak or occasionally absent. Frontal setae mostly well developed, Thoracic horn stalked, very long, filamentous, and smooth or robust, tapering and covered with spinules. Three precorneals, 3–4 antepronotals, at least one postorbital and 4 dorsocentrals present; dorsocentrals in two pairs or equidistant. Wing sheath smooth without pearls or nose.

Tergite I bare or with a few posterior spinules, II with weak median or posteromedian shagreen; tergites III–VI with median portion covered with single mostly subrectangular patch of often coarse spinules; tergites III–V with 4–7 rows of anteriorly directed spinules posteriorly on tergites or more usually on conjunctives; tergite VII–IX with weak anterior group shagreen, occasionally with additional median shagreen. Sternites I bare, II–VIII with lateral or anterolateral shagreen; II–III or IV often with additional large patch of spinules. Pedes spurii A on sternites IV–VI or VII. Pedes spurii B well developed, spinulose or granulose or occasionally absent ( O. lamellatus ), sometimes present also on tergite III. Caudal hooklets on tergite II 40 –160; in 2–6 rows. Segments II–V each with 3 L setae , VI and VII each with 3–4, and VIII with 4–5 L setae .

Anal lobe either large, rounded, without apical spurs, but with minute to very long lateral threads, and apically curved, subequal anal macrosetae; or slightly extended with heavy spines on tips and vestigial macrosetae ( O. rousellae ). Male genital sac nearly reaching to or slightly overreaching anal lobe.

Larva

Moderately large larvae, up to 8.6 mm long. Head capsule brown to dark brown.

Antenna with 5 segments, antennal ratio 1.7–3.0. Ring organ in basal third. Lauterborn organs weak to moderately developed. Labrum with one branch of S I occasionally split into weak branches; two labral lamellae each with 3–7 spines sometimes present; about 12 chaetae and 2–5 spinulae. Pecten epipharyngis consisting of 3 subequal spine­ to lobe­like teeth. Chaetulae laterales all smooth or one chaetulae laterales slightly serrated. Premandible simple or bifid, brush present and distinct to vestigial or absent. Mandible often without seta interna. Mentum with 13–17 teeth, median tooth slightly wider than first lateral tooth to more than four times as wide, ventromental plate occasionally with weak setae underneath on cardo. Pecten galearis apparently absent.

Claws of anterior parapods strongly serrated. Body with simple setae , some long and robust. Procercus higher than wide, with 6–7 anal setae ; supraanal seta about 1/3 to 1/4 as long as anal setae . Anal tubules shorter than posterior parapods, rounded, subequal or one pair slightly shorter.