Pleidae. Paraplea frontalis (Fieber).Helotrephidae. Helotrephes semiglobosus St?l, Hydrotrephes visayasinensis Zettel, Hydrotrephes balnearius (Bergroth), Tiphotrephes indicus (Distant).Notonectidae. Y-27632 2HCL Anisopinae: Anisops cameroonensis Signoret, Anisops sardea Herrich-Sch?ffer, Buenoa uhleri Truxal; Notonectinae: Notonecta glauca Linnaeus, (Fabricius), Enithares bergrothi Montandon, Nychia sappho Kirkaldy.Corixidae. Corixinae: Agraptocorixa hyalinipennis (Fabricius), Corixa dentipes (Thomson), Corixa punctata (Illiger), Ectemnostegella montana Lundblad, Hesperocorixa linnaei (Fieber), Cymatiinae: Cymatia coleoptrata (Fabricius), Stenocorixinae: Stenocorixa protrusa Horv��th.Diaprepocoridae. Diaprepocoris zelandiae Hale.Micronectidae. Micronecta quadristrigata Breddin.
Specimens of the Potamocoridae were not available for the purpose of the present study. 2.2. Terminology Used for Descriptions of the Apical Sensilla With respect to the external morphology of the sensilla, in this study they are classified according to the morphological criteria established by Altner and Prillinger [6], McIver [8], and Zacharuk [7]. The receptor functions of the sensilla of the insects have been distinguished based on the morphological and ultrastructural features described by a number of authors [4, 6�C8, 28, 29]. Such information is also used for the interpretation of newly described labial sensilla such as clubbed-like sensillum (CBS), paddle-like sensillum (PDS), cupola-like sensillum (CUS), finger-like sensillum (FRS), freniale-like sensillum (HLS), chaetic sensillum with a divided tip (CHD), star-like sensillum (STS), and multilobed sensillum (MPS).
The remaining types of sensilla mentioned in the present paper (Table 1) are known from previous descriptions of other authors [4, 6�C8, 15, 24]. Table 1 includes information about functional and morphological classifications and provides definitions of the sensilla of insects used for current descriptions of the twenty-four types of labial sensilla in the Nepomorpha. Abbreviations of sensilla used throughout the paper are explained in the last column.Table 1Terminology and classification of labial sensilla. 3. Results3.1. Morphology and Categories of the Labial SensillaFunctionally, the labial sensilla are classified into two categories: mechanoreceptive and chemoreceptive sensilla, within which there can be determined twenty-four types (21 types of mechanosensilla, three types of chemosensilla) on the basis of their external appearance and location.
The main external morphological characters indicating the types of sensilla are pores system (visible or not), the manner in which the sensilla are sunken with respect to the surface of the labium (flexible or inflexible sockets), and the shape of the sensilla.The twenty-four Entinostat types are grouped as follows.