Notes on some toad bugs from China (Hemiptera, Heteroptera, Gelastocoridae)

Abstract The three species of Nerthra Say, 1832 (Hemiptera: Heteroptera: Gelastocoridae) occurring in China are reviewed. Dorsal habitus photographs of the two species, Nerthra asiatica (Horváth, 1892) and Nerthra indica (Atkinson, 1889), are provided, accompanied by illustrations of male genitalic structures and female ventral aspect of posterior abdominal segments. The male of Nerthra asiatica is recorded and reviewed for the first time.


Introduction
Toad bugs (Gelastocoridae) are a remarkable group of aquatic bugs (Nepomorpha) which are derived from aquatic ancestors and have become secondarily terrestrial (Hebsgaard et al. 2004). Gelastocoridae contains three recent genera and approximately 103 species distributed worldwide, but much more prevalent in the tropics (Polhemus 1995). It is divided into two subfamilies, Gelastocorinae and Nerthrinae. Recent Gelastocorinae (two genera) are reported in only in America, from southern Canada to north Argentina (Štys and Jansson 1988;Chen et al. 2005), but there is one fossil species, Gelastocoris curiosus Poinar & Brown, 2016 described from Burmese amber (Poinar and Brown 2016). The Nerthrinae includes one fossil genus, Cratonerthra Martins-Neto, 2005 with two species (Ruf et al. 2005), and one recent genus, Nerthra Say, 1832, currently including 92 valid recent species, of which nine species occur in south-eastern Asia west of Wallace line, and three species present in China (Kment and Jindra 2008, Xie and Liu 2013, Faúndez and Ashworth 2015.

Systematics
Head. Apical tubercle absent, lateral and superapical tubercles small, irregular in shape, not sharply pointed. Thorax. Pronotum widest at transverse furrow, a little narrower than abdomen; lateral margins of pronotum parallel or nearly so, anterior and posterior margin weakly sinuate; surface coarsely granulate. Scutellum elevated, apex slightly lobed, with tumescences at the middle of the lateral margins. Hemelytra not extending to the end of the abdomen, membrane well developed; embolium with the basal half of the lateral * these measurements are from Polhemus andPolhemus 2012 andTodd 1955. margin nearly straight, not expanded laterally at middle. Connexivum greatly expanded laterally in females. Bristles short or moderately long, clavate, slightly curved, bristles in rows and clumps on hemelytra and in clumps on scutellum and pronotum.
Abdomen. Abdominal V-IV sternites of male mostly asymmetrical, ninth sternite rather oval, wider than long, not as long as eighth sternite; seventh sternite sternite about half as long as eighth sternite; fifth sternite very short medially (Fig. 2E). In female, abdomen nearly symmetrical. Lobes of ovipositor slightly projecting posteriorly; posterior margin of last visible abdominal sternite triangularly emarginate (Fig. 2F).
Head. Apex of head with four tubercles, one at the apex is not visible in the dorsal view, the others sometimes rather indistinct (Fig. 1C-D).
Thorax. The lateral margins of the pronotum markedly asymmetrical, pronotum about as wide at anterior third as at the level of the transverse furrow. Scutellum el- evated, tumescent laterally and at apex, with curved ridge paralleling sinuosity of posterior margin of pronotum. The outline of the ovipositor was the same and the ventral submarginal tumescences on the last visible abdominal sternite absent. Hemelytra not quite reaching end of abdomen in the females, membrane well developed; embolium narrow at base, dilated before middle, anterior portion and apex of dilation more or less rounded. Ventral surface and the apex of the fore, middle, and hind legs dark brown.
Abdomen. Abdomen greatly expanded laterally in females. Bristles mostly short and clavate, groups of long black bristles on basal tumescences and median part of pronotum. Abdominal sternites of male mostly asymmetrical, but nearly symmetrical in female. Lobes of ovipositor asymmetrical slightly lobed and projecting posteriorly. Ninth sternite wider than long, not as long as eighth sternite; seventh sternite sternite about half as long as eighth sternite; fifth sternite very short medially. Right paramere swollen apically and stick out at middle.
Remarks. Body shape most closely related to N. lobata (Montandon, 1899) from which it may be separated by the male genitalia shape (Fig. 3A-D), the smaller ovipositor lobes which are less projecting, and the lack of lateral submarginal tumescences of the last visible abdominal sternite in the females.
Abdominal sternites of female nearly symmetrical except for posterior margin of last sternite, which is slightly emarginated, but with apex slightly convex just below the lobes of the ovipositor, the latter somewhat rounded and the left one overlapping the right. Abdominal sternites of male rather small, last visible abdominal sternite wider than long, nearly twice as long as seventh sternite, which has the right side elongate, spatulate.
Clasper of male rather sickle-shaped, but nearly straight, very slightly enlarged at apex then tapering to a blunt point.
Notes. During the daytime this species hides in wet mud or sand, or under stones or plant debris . Nieser and Chen (2005) observed these toad bugs burrowing in the sand on a beach in the south of Taiwan. In view of its inability to fly, its wide distribution is attributed to dispersion by drift on plant debris (Todd 1960). The authors have not seen this species, and distribution data for this species was collected from the published literature.
Distribution. China (Taiwan), Japan, Philippines, Malaysia, Indonesia, Australia (Kment and Jindra 2008). manuscript and providing important suggestions. This study is supported by the "Young Talents" Project of Northeast Agricultural University (No. 16QC04), the Natural Science Foundation of Heilongjiang Province, China (No. C2017017) and Key Laboratory of Soybean Biology, in Chinese Ministry of Education, Northeast Agricultural University (SB16B01).