Micronecta Kirkaldy 1897
Creators: name: Ha, Tuyet Ngan
name: Tran, Anh Duc
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hemiptera
Corixidae
Micronecta

description: Genus Micronecta Kirkaldy, 1897
Micronecta Kirkaldy, 1897b: 260
(type species: Notonecta minutissima Linnaeus, 1758).
Comparative notes
In Southeast Asia, only two genera of Micronectidae occur: Micronecta Kirkaldy, 1897 and Synaptonecta Lundblad, 1933. They are closely related, but there are significant structural differences between the two genera, as summarised by Wróblewski (1972a), Nieser (2002b), and Chen et al. (2005).
The genus Micronecta can be recgonised by the following characterstics: the vertex is usually convex and rarely flattened; the pronotum is usually well-developed and convex; fore tibia and pala of the male are separated; the strigil on abdominal tergite VI is usually present; the apex of the membrane in the brachypterous morph is truncate or broadly rounded. The body of species of Micronecta is ovate or subparallel sided, with length between 1.0 and 4.4 mm.
In contrast, Synaptonecta can easily be separated from the abundant Micronecta by the fusion of the fore tibia and pala in both sexes, the concave vertex, and the pointed apex of the membrane in the brachypterous morph (also see Wróblewski 1972a; Chen et al. 2005). The body of species of Synaptonecta is ovate, with length between 1.8 and 2.6 mm.
Remarks on the current subgeneric classification of Micronecta Kirkaldy, 1897
Several subgenera of Micronecta were established by Hutchinson (1940) and Wróblewski (1962, 1967). Hutchinson (1940) also introduced several species groups of Micronecta, recognised below the subgeneric rank, but this species group classification was hardly used by subsequent entomologists. However, many species were not formally assigned to any subgenera because they did not fit the definition of any subgenus (Štys & Jansson 1988; Nieser 2000; Tinerella 2008, 2013). In many cases, those species which do not fit any subgenus were just placed, although tentatively, into the nominate subgenus Micronecta (see Jansson 1995). This classification scheme was questioned by Tinerella (2008, 2013), but no resolution was made. Tinerella (2008, 2013) only attempted to reconstruct phylogenetic relationships between micronectid genera occurring in New Guinea and Oceania. Nieser (2000, 2002b), and Nieser & Chen (1999) refrained from using a subgeneric classification for the same reason, but subsquently Nieser et al. (2005) and Chen et al. (2015) used a subgeneric classification again, without clear explanation about the switch in their opinions. Nieser et al. (2005) even described a new subgenus, Unguinecta Nieser, Chen & Yang, 2005, to include several species.
It is notable that several subgenera, e.g., Ctenonecta Wróblewski, 1962, Indonectella Hutchison, 1940, Lundbladella Wróblewski, 1967, and Pardanecta Wróblewski, 1962, were defined just based on only a few aberrant morphological features, which are potentially homoplasious (e.g., the shape of the palar claw of the male, the absence of a strigil in some subgenera, the shape of the free lobe of tergite VIII, or even the general morphology of the left paramere). On the other hand, the diversity of Micronecta is still poorly known; thus, the current taxonomy of Micronecta does not yet satisfactorily reflect natural relationships among subgeneric taxa. Our present paper illustrates this situation, with a high number of previously unknown species showing an aberrant morphology. A comprehensive phylogenetic analysis is certainly needed for resolving the systematics of the genus Micronecta. However, this type of work requires extensive taxon sampling across the very large distribution range of Micronecta as a whole, together with sampling of relevant DNA sequence data. This is beyond the scope of our present study, but we hope it can be achieved in the future.
While pending such comprehensive phylogenetic analyses, we perceive that the current subgeneric classification is still useful for the identification and comparative morphology of species of Micronecta, and to some extent it reflects the great diversification of the genus.Therefore, we indicate the subgeneric position of all species treated in the present paper, largely according to definitions of subgenera by Wróblewski (1962, 1967) and Nieser et al. (2005). Among the 11 recognised subgenera, Mesonecta Poisson, 1938 and Micronectella Lundblad, 1933 do not occur in Vietnam. We note that some species in this paper do not fit any currently defined subgenus, and are thus still not formally assigned, i.e., M. caperata sp. nov., M. tarsalis, and M. fugitans Breddin, 1905; and we treat them under the Incertae sedis section.
To assist in the quick identification of Micronecta for readers who are not familiar with the subject, we collate and re-assess diagnostic features of all current subgenera and provide a key to them, as follows.
Key to current subgenera of Micronecta Kirkaldy, 1897 (applicable to male specimens only)
1. Strigil absent ...................................................................................................................................... 2
– Strigil present .................................................................................................................................... 4
2. Palar claw broad, apically rounded..................................... subgenus Micronectella Lundblad, 1933
– Palar claw narrow and straight .......................................................................................................... 3
3. Median lobe of sternite VII with four long setae, apex angular; free lobe of tergite VIII subparallel sided, posterior margin concave (Fig. 6B) .......................... subgenus Indonectella Hutchison, 1940
– Median lobe of sternite VII without long setae, nearly obtuse, both sides convex;free lobe of tergite VIII distally narrow with mesial angle produced (Fig. 6F) ..... subgenus Lundbladella Wróblewski, 1967
4. Palar claw subovate with deep lateral incision (Fig. 2H); middle tibia with combs of 25 or 29 short and thick, erect setae ...........................................................subgenus Ctenonecta Wróblewski, 1962
– Palar claw not as above; middle tibia without combs of short setae ................................................ 5
5. Pala with secondary narrow claw (Fig. 23A) ................................................................................... 6
– Pala without secondary claw ............................................................................................................ 7
6. Free lobe of tergite VIII apically rounded; shaft of left paramere broad, slightly sinuate, with wide truncate apex .............................................................................. subgenus Mesonecta Poisson, 1938
– Free lobe of tergite VIII with produced lateral angle (Fig. 23B, E); shaft of left paramere long and narrow, tapering apically (Fig. 23D, G) .............. subgenus Unguinecta Nieser, Chen & Yang, 2005
7. Palar claw slender with hooked apex or with a notch before apex (Figs 24A, 25A, E)...................... ...... [incertae sedis, e.g., M. fugitans Breddin, 1905, M. tarsalis Chen, 1960, M. caperata sp. nov.]
– Palar claw not modified as above ..................................................................................................... 8
8. Palar claw narrow and nearly straight (Fig. 2A)................ subgenus Basileonecta Hutchinson, 1940
– Palar claw broader and usually widened apically ............................................................................. 9
9. Palar claw usually large, strongly widened apically (e.g., Figs 8A, 9F); shaft of left paramere platelike with subparallel sides (e.g., Figs 7C, 8F, 9E) ....................subgenus Micronecta Kirkaldy, 1897
– Palar claw not or moderately widened apically (Figs 3G, 22D); shaft of left paramere thicker, not plate-like ......................................................................................................................................... 10
10. Median lobe of sternite VII elongate, tongue-shaped, with a rounded tip; free lobe of tergite VIII sigmoid (Fig. 22A, E); left paramere with a sickle-shaped apex (Fig. 22C, G).................................. ............................................................................................subgenus Sigmonecta Wróblewski, 1962
– Median lobe of sternite VII less developed; free lobe of tergite VIII with expanded, truncate apex (Figs 3A, D, 4A, D, 20B); left paramere not as above ....................................................................11
11. Body length at most 2.4 mm; median lobe of sternite VII with one or two long setae ....................... .......................................................................................... subgenus Dichaetonecta Hutchison, 1940
– Body length 2.4–3.3 mm; median lobe of sternite VII usually with four long setae........................... ............................................................................................ subgenus Pardanecta Wróblewski, 1962
description: Published as part of Ha, Tuyet Ngan & Tran, Anh Duc, 2021, Taxonomy of Micronectidae (Heteroptera: Nepomorpha) from Vietnam, with descriptions of 11 new species, pp. 1-82 in European Journal of Taxonomy 756 on pages 3-5, DOI: 10.5852/ejt.2021.756.1407, http://zenodo.org/record/5033010