Onconeura, Andersen, Trond & Saether, Ole A., 2005

Andersen, Trond & Saether, Ole A., 2005, Onconeura, a new Neotropical orthoclad genus (Chironomidae, Orthocladiinae), Zootaxa 957, pp. 1-16 : 2-7

Onconeura new genus

Thienemanniella sensu Saether 1981 , pro parte nec Kieffer 1911. Gen. n. near Thienemanniella Mendes et al. 2004 .

Type species

Onconeura undecimata new species by present designation.

Other included species

Thienemanniella semifimbriata Saether 1981 .

Generic diagnosis

The imagines are separable from those of other Orthocladiinae except Corynoneura Winnertz 1846 , Thienemanniella Kieffer 1911 , Physoneura Ferrington & Saether 1995 , Tempisquitoneura Epler in Epler & de la Rosa 1995, Ichthyocladius Fittkau 1974 , and Notocladius Harrison 1997 by having R1, R2+3, and the costa retracted and swollen forming a thick clavus which terminates at or before the midpoint of the wing. The following combination of characters will separate the genus from the other members of the group: bare eyes; female pedicel without setae; tergites without raised, median area of setae and with 4–8 setae in median transverse row; posterior sternites with single median and 2 very weak posterior setae; anal lobe well developed; all trochanters with dorsal keel; hind tibial apex not broadened; tarsomere 4 not noticeably cordiform; male transverse sternapodeme well developed with strong oral projections; superior volsella separate, low but distinct; female gonocoxite IX well developed but adpressed, with a few setae; coxosternapodeme with a few spine­like anterior projections; and apodeme lobe and labia large.

The pupa differs from that of other genera without a thoracic horn and with an anal lobe fringe by having 4–7 rows of pearls on the wing sheath, one weak non­taeniate macroseta, anal lobe with strong seta on inner margin, and tergal conjunctives with posterior rows of up to 10 strong recurved spines (hooklets).

The larva has the antennae about 1/3 the length of the head, as opposed to 1/ 4 in Tempisquitoneura , about 1/2 to 3/ 4 in Thienemanniella , and about as long as the head in Corynoneura . The S I is simple while it is bifid in Tempisquitoneura and Notocladius ; the mentum has 3 subequal teeth and 5 pairs of lateral teeth of which the first is adpressed to the outer median tooth. The posterior parapods are more than 5X as long as medially wide.

Etymology

From the Greek oncos, hook, referring to the Eukiefferiella ­like conjunctive hooklets and ­ neuron, nerve, sinew, but here used as an indication of relationship with similar genera.

Description

Imago

Small species, wing length about or less than 1.0 mm.

Eye bare, reniform, without dorsomedian elongation. Antenna with 11–12 flagellomeres in male, 5 in female; fully plumed; groove in male beginning on flagellomere 2; sensilla chaetica present on flagellomeres 2, 3, and ultimate; apex strongly clubbed and rounded; male AR lower than 1.0. Palpomeres normal; palpomere 3 with 1–2 short lanceolate sensilla clavata. Temporals reduced in number. Tentorium long, narrow, tapering to point. Stipes normally developed. Cibarial pump with anterior margin deeply concave, cornua strongly developed. Clypeus with several setae.

Antepronotal lobes not reduced medially, with several weak lateral antepronotals. Acrostichals absent; dorsocentrals uniserial, few prealars, single supraalar present or absent. Scutellum with few transversely uniserial setae.

Wing membrane without setae, with fine punctuation. Anal lobe well developed, but not projecting. Costa apically fused with R1 and R2+3 forming a thick clavus well proximal to wing midpoint in male, at about mid point in female; R4 (or R4+5) and R5 (or M1) running together from RM to near apex, separated basally, nearly fused and becoming evanescent apically; Cu1 slightly sinuous; FCu far distal to RM; postcubitus ending far past cubital fork; anal vein ending below or slightly distal to cubital fork. Brachiolum with 1 seta; clavus with apical seta; R1 with a few setae on clavus in female, bare in male; other veins bare. Squama bare. Sensilla campaniformia about 7–8 basally on brachiolum as well as apically on brachiolum, 3 below setae on brachiolum; 1 present on RM.

Front leg ratio about 0.7–0.8. Trochanters with dorsal keel, best developed on fore trochanter. Tibial spurs and hind tibial comb normal. Hind margin of tarsomeres 1–3 with double row of shorter, thicker, bluntly tipped setae, best developed on mid and hind tarsomere 1. Tarsomere 4 barely cordiform. Sensilla chaeticae present approximately at basal 1/4 to 1/2 on ta1 of middle and sometimes hind leg. Pulvilli absent.

Tergites with median transverse band of 4–8 setae. Posterior sternites with 1 median and two very weak posterolateral setae.

Hypopygium short, without anal point; tergite IX with several weak setae, more or less weakly emarginated with two weak protrusions. Laterosternite IX with few setae. Transverse sternapodeme slightly convex, oral projections strongly developed. Phallapodeme well sclerotized, aedeagal lobe well developed with sclerotized apicomedian margin. Virga absent. Gonocoxite well developed; superior volsellae low but relatively well developed at least sometimes fused basally; inferior volsella well developed. Gonostylus without crista dorsalis, widest near apex, megaseta simple.

Female genitalia with straight gonocoxapodeme ending on base of gonapophysis VIII. Gonocoxite well developed, but adpressed, with few setae. Tergite IX with apical notch, with several setae. Segment X normal. Postgenital plate weak, indistinct, bluntly triangular. Cercus relatively large. Gonapophysis VIII not divided. Apodeme lobe large and distinct, partly sclerotized. Labia large and bare, fused basally, notched apically. Coxosternapodeme with median curves and a few spine­like anterior projections. Seminal capsules smaller than cerci, ovoid, darkly sclerotized full length, neck placed anterolaterally. Spermathecal ducts anteriorly narrow, nearly straight or with loop, wider posteriorly and nearly straight, with common opening.

Pupa

Small pupa, less than 3 mm long. Exuviae pale greyish brown.

Cephalic tubercles and frontal warts absent. Frontal setae very weak and transparent, slightly taeniate or long and strong, on sclerotized tubercles on frontal apotome. Frontal apotome wrinkled or smooth. Thoracic horn absent. Thorax tuberculose anteromedially, rugulose and wrinkled laterally and posteriorly. Wing with several rows of pearls, without nose. Three precorneals, 2 median and apparently 1 lateral antepronotals, at least one postorbital, and 4 dorsocentrals arranged in two pairs present. One precorneal and posterior dorsocentral conspicuously strong.

Tergite I without shagreen; II–IX with shagreen; weak on II; strong on III–VI with area in front of posterior spines nearly bare. Posterior margin of II–VIII with 1–3 transverse rows of spines grading over into more anterior coarse shagreen spinules. Conjunctives I/II (II/III) – VI/VII (VII/VIII) with strong hooklets, 3–10 on conjunctives II/III to VI/VII. Sternites I bare; II with sparse median shagreen consisting of fine needle­like, pale spinules becoming stronger posteriorly; III–VIII with sparse shagreen becoming coarser on posterior sternites; IX bare. Sternites IV–VIII in male, IV–VII in female with weak posterior spines. Female sternite VIII with broad and low posterior projection with median suture. Pedes spurii A and B absent.

Segment I with 2 L setae, II–VII each with 4, VIII with 3 L setae, L2 sometimes slightly taeniate. Tergites and sternites apparently with 1 pair of O setae in C5 pattern, i.e., ventral O setae laterad of dorsal O setae.

Anal lobe well developed with fringe in apical 1/3 of uniserial taeniae, anterior few taeniae often spine­like, preapical taeniae sometimes very long, 1–3 spines posterior to apical taenia; inner margin of anal lobe with long non­taeniate seta, one short, non­taeniate macroseta dorsal to bases of anal lobe fringe. Genital sacs of male and female not extending to apex of anal lobe.

Larva

Head capsule about 1 3/4 as long as wide, somewhat wedge shaped. Antenna about 1/ 3 as long as head capsule; basal segment about twice as long as flagellum, with ring organ 1/3 from base and 2 setae about at 2/3; antennal segment 2 slightly longer than combined length of 3–5. Lauterborn organs well developed, style weak. Blade shorter than flagellum. Labrum with S I and S III apparently weak and simple; S II [labral seta S I in Saether (1981), see Epler & de la Rosa (1995)] strong, situated on tubercle; at least 3 chaetae. Pecten epipharyngis of 3 simple spines. Chaetulae laterales 4–6 pairs, chaetulae basales apically bifid. Premandible simple, with well developed brush. Maxilla with long lacinial chaetae. Mandible with 4 inner teeth, apical tooth slightly shorter than combined width of first 2 inner teeth, seta interna with about 7 plumose branches. Mentum with 3 subequal teeth and 5 pairs of lateral teeth of which the first is adpressed to outer median tooth. Ventromental plates narrow, broader posteriorly. Setae submenti situated well below base of outer lateral tooth of mentum.

Claws of anterior parapods serrate. Procercus higher than wide, with 3–4 anal setae. Posterior parapods long, more than 5X as long as medially wide. Anal tubules much shorter than posterior parapods.

Systematics

The generic assignment of O. semifimbriata is discussed by Saether (1981) and Epler & de la Rosa (1995). Onconeura and Tempisquitoneura are very similar and closely related. The relationships between these two genera, Thienemanniella and Corynoneura , remain uncertain because in some features the genera are intermediate between Corynoneura and Thienemanniella , and in others apparently more plesiomorphic than in Thienemanniella . However, the polarity of apparent decisive trends will depend on which genus or group of genera forms the sister group of the Corynoneura group. The presence of large caudal hooklets on tergal conjunctives are conspicuous both in Onconeura and in Tempisquitoneura , and in the new species described here the hooklets are every bit as conspicuous as those in the Eukiefferiella group. Saether (1977) placed the Corynoneura group as sister group to reduced Orthocladiini sensu Brundin and Metriocnemini sensu Brundin combined, i.e., with some plesiomorphic groups removed, with Heterotanytarsus Spärck, 1923 as sister group to all three groups combined and the Eukiefferiella group as sister to all the above. That is, the Corynoneura group was just two nodes removed from the Eukiefferiella group. Onconeura and Tempisquitoneura , however, indicate that the groups either are sister groups or that the Eukiefferiella group is paraphyletic because it includes the Corynoneura group.

Characters in common for all the genera of the two groups include absence of pedes spurii A and B of the pupa; sexual dimorphism of sternite VIII of the pupa; gonapophysis VIII of the female genitalia undivided; and ventromental plates of the larvae narrow, inconspicuous, widest posteriorly, and without setae underneath.

All imagines of the Corynoneura group and several of the Eukiefferiella group lack acrostichals, have retracted R4+5, lack a squamal fringe, have cordiform ta4 shorter than ta5, and except for Physoneura no anal point, and no virga. All pupae of the Corynoneura group and many species of the Eukiefferiella group lack a thoracic horn. The caudal hooklets on the tergal conjunctives or posterior on the tergites otherwise is found only in Clunio Haliday 1855 , which could be an aberrant relative. The seta arising from the inner margin of the anal lobe is unique to Tvetenia Kieffer 1922 , Corynoneura , Tempisquitoneura , Thienemanniella , Notocladius , and Onconeura . The pupal wing sheaths have pearl rows in Dratnalia Saether & Halvorsen 1981 , Tvetenia , Corynoneura , Tempisquitoneura , and Onconeura , whereas such rows otherwise among the orthoclads occur only in the Heterotrissocladius group. Most larvae of both groups have all S setae simple. The Lauterborn organs usually are well developed. The pecten epipharyngis always consists of three simple spines and often the median chaetulae laterales is of the same shape, making it appear as though there are five spines in the pecten epipharyngis. The posterior parapods often are longer than normal. The above characters clearly support the monophyly of the combined Corynoneura and Eukiefferiella (or Cardiocladius ) groups. However, according to Ferrington & Saether (1995) the placement of Physoneura in the Corynoneura group is somewhat uncertain because the immatures and the female are unknown.

Within the Corynoneura group, large caudal hooklets and pearl rows in the pupa and normal larval antennae should, for instance, be regarded as plesiomorphous features. Schlee (1968) considered five morphoclines for the larvae, all of them involving progressive elongation, i.e., the longest structures are considered apomorphic, of the head capsule, of the antennae, of the anterior parapods, of the posterior parapods, and of the procerci. According to Epler & de la Rosa (1995), Tempisquitoneura lies at the plesiomorphic end of the gradient for the second and the last and occupies an intermediate state for the other trends. In Onconeura , the antenna is longer than in Tempisquitoneura , but not as long as in Thienemanniella , whereas the head capsule length/width, elongation of the parapods, and length of the procercus are about as in Tempisquitoneura . The reduction of the L setae, anal lobe fringe, and anal macrosetae in the pupae of Onconeura and Tempisquitoneura could be regarded as synapomorphies. However, there is no fringe in the pupae of the Eukiefferiella group and the lateral abdominal setae are about as in Onconeura . The fringe in the Corynoneura group thus could be secondarily developed, making a partly fringed anal lobe more plesiomorphic than a full fringe, and the L setae of Onconeura representing the most plesiomorphic step of a trend with reduction in Tempisquitoneura and stronger development in the other two genera.

Mendes et al. (2004) did a generic­level parsimony analysis of all genera near Eukiefferiella Thienemann 1926 and Corynoneura , except Notocladius and selected genera of Orthocladiinae; Onconeura was included as Gen. n. near Thienemanniella . In all results, when characters were unweighted, weighted, or reweighted, Tempisquitoneura formed the sister group of Corynoneura and Thienemanniella combined, with Onconeura as the sister group of the three combined. Also, in all results, the Corynoneura group, which also included Physoneura and Ichthyocladius , formed a monophyletic group within a paraphyletic Eukiefferiella group. Notocladius was excluded from the analysis because several of the characters used by Mendes et al. (2004), such as presence or absence of a superior volsella, shape of the phallapodeme, and presence or absence of a keel on the trochanter, are not mentioned in the description by Harrison (1979), and because the larva is tentatively associated. However, adding Notocladius to the data matrix in Mendes et al. (2004) places the genus as the sister group of Corynoneura , Thienemanniella , Onconeura , and Tempisquitoneura combined when characters are not weighted, but as the sister group of Corynoneura and Thienemanniella alone when some characters are weighted. While the strict consensus trees for unweighted and reweighted characters differ in several details, no longer indicating the monophyly of a combined Corynoneura—Eukiefferiella group, the results when some characters are weighted are identical to those obtained by Mendes et al. (2004, Figs. 38, 39) with Notocladius inserted above Tempisquitoneura .