Omicrogiton coomani Balfour-Browne, 1939

Jia, Fenglong, Lin, Renchao, Li, Bijun & Fikacek, Martin, 2015, A review of the omicrine genera Omicrogiton, Mircogioton and Peratogonus of China (Coleoptera, Hydrophilidae, Sphaeridiinae), ZooKeys 511, pp. 99-116 : 102

Taxon classification Animalia Coleoptera Hydrophilidae

Omicrogiton coomani Balfour-Browne, 1939 Figs 3-4, 17-18, 23-24

Omicrogiton coomani Balfour-Browne, 1939: 471.

Type material examined.

Lectotype (hereby designated): dissected male (BMNH): "LACTHO / Tonkin. / de Cooman // Andrewes / Bequest / B. M. 1922-22 // Omicrogiton / coomani Paratypes! / J. Balfour-Browne det. // A. d’Orchymont det. / Omicrogiton / insularis / d’Orchymont // Coll. d’Orchym.”. Paralectotypes: 1 unsexed spec. (BMNH): same data as the lectotype [this specimen was originally pinned on the same pin as the lectotype, and is now moved to the seperate pin to whoch copies of the aforementioned label are attached]; 1 unsexed specimen (BMNH): " LACTHO / Tonkin. / de Cooman // C. G. Champion / Brit. Mus. / 1925-42 // A. d’Orchymont det. / Omicrogiton / insularis / d’Orchymont // PARATYPE // Omicrogiton / coomani Type! / J. Balfour-Browne det."; 1 unsexed specimen (BMNH): " LACTHO / Tonkin. / de Cooman // C. G. Champion / Brit. Mus. / 1925-42 // A. d’Orchymont det. / Omicrogiton / insularis / d’Orchymont // Omicrogiton / coomani Paratype! / J. Balfour-Browne det.".

Additional material examined.

CHINA: Guangdong: 3 males, 4 females, 87 unsexed spec. (SYSU): Zhaoqing, Heishiding Natural Reserve, 4-6.x.2013, Fenglong Jia, Ye Jia, Bingjie Chen, Renchao Lin et Weilin Xu leg.; 2 males, 2 females, 15 unsexed spec. (SYSU): Fengkai, Heishiding Natrual Reserve, 179 m, 12.v.2011, Song Keqing leg.; 138 spec. (SYSU): Fengkai, Heishiding Natural Reserve, 20.xi.2010, Fenglong Jia leg.; 88 spec. (SYSU): Fengkai, He’erkou, in decaying banana trunks, 14.viii.2010, Fenglong Jia leg.; 14 spec. (SYSU): Fengkai, Heishiding Natural Reserve, 2.v.2011, Fenglong Jia leg.; 2 males, 1 female, 44 spec. (SYSU): Fengkai, Guangling village, 9.x.2010, Yan Mei, Lijun Yang, Yali Yu leg.; 1 male (SYSU): Fengkai, Yanshuitian, 8.x.2010, Yan Mei et Lijun Yang leg. 1 male, 11 unsexed specimens (NMPC): W of Qixing, Heishiding nature reserve, rotting trunks of banana along the dried-up stream in the primary lowland forest, 190-260 m a.s.l., 23°27.9'N 111°54.3'E, 1.-3.v.2011, Fikáček & Hájek leg. Hainan: 1 male (NMPC): Limushan Mts., 19°9.1-9.2'N 109°45-46'N, along the road, 550-750 m a.s.l., rotting banana trunks at the stream in secondary forest, 5.v.2011, Fikáček & Zhao leg. Hong Kong: 2 males, 3 females, 25 unsexed spec (AFCD): Hong Kong, Wutongzhai, 27.ix.2013, F.L. Jia, Yingming Lee & Eric Chen leg. VIETNAM: 2 males (SYSU): Tonkin, Hoa-Binh, leg. A. de Cooman, with labels "Omicrogiton insularis d’Orchym.” [handwritten] and "En-121415 [En-121416, respectively], Sun Yat-sen University, Biomuseum" [transcript from Chinese]; 1 male, 1 female (IZCAS): Tonkin, Hoa-Binh, leg. A. de Cooman.

Diagnosis.

Body length 1.9-2.1 mm, width 1.2-1.3 mm. Head and elytra brown; scapus ca. 3.5 × as long as antennomeres 2-5 combined. Interstices of pronotum with fine mesh-like microsculpture; prosternum strongly tectiform. Phallobase ca. half as long as parameres, without distinct manubrium; paramere without strongly sclerotized S-shaped portion, rather wide throughout, weakly sinuate on outer margin, apex semicircular; median lobe slightly narrower than paramere, wide basally, then abruptly narrowing and rather narrow in apical half, apex narrowly rounded, gonopore small, apical.

Differential diagnosis.

Omicrogiton coomani differs from all other species of the genus except of Omicrogiton cheesmanae from New Hebrides by the presence of the fine microsculpture on pronotal interstices. It may be also easily distinguished from all other species of the genus by the morphology of the aedeagus, which lacks the strongly sclerotized S-shaped sclerite of the paramere, and has narrow median lobe with small apical gonopore.

Remark.

When Balfour-Browne (1939) checked the material of Omicrogiton insularis Orchymont, 1919 deposited in BMNH, he found that the specimens from "Tonkin (Lac Tho)" (i.e. Lac Tho in the Hoa Binh Province in northern Vietnam) differ from those from Engano Island near Sumatra (type locality of Omicrogiton insularis ) and described them under the name Omicrogiton coomani . Since the diagnosis of Omicrogiton coomani was very short and it was only presented in the discussion concerning another species of the genus from New Hebrides, the species remained virtually unknown and unrecognized in the collections. The aedeagus of the dissected type specimen of Omicrogiton coomani (Fig. 17) really differs from that of Omicrogiton insularis and we can therefore confirm that Omicrogiton coomani is a separate species.

Within this study, we are showing that Omicrogiton coomani may co-occur syntopically with other species of the genus, from which it may be distinguished by male genitalia only. To fix the identity of the species and prevent any future confusion, we are hence designating here the only dissected syntype specimen as the lectotype of Omicrogiton coomani . Aedeagus of this specimen is shown in Fig. 17.

Biology.

All examined specimens were found in the decaying banana trunks, typically in still standing trunk bases which are decaying after the apical part of the plant was cut or broken.

Distribution.

China (Guangdong, Hong Kong), northern Vietnam. New for China.