The Pleidae (Hemiptera, Heteroptera) of Thailand, with the descriptions of two new species and a discussion of species from Southeast Asia

Abstract The family Pleidae is represented in Thailand by four species in the genus Paraplea. Two of these species, P. frontalis and P. liturata, are widespread and relatively common in Southeast Asia. Two other species, P. lateromaculata Cook, sp. nov. and P. melanodera Cook, sp. nov., are described and only known from Thailand. Full descriptions are provided for all four species. The distributions of these species are discussed, with an emphasis on Thailand. Paraplea frontalis, P. liturata, and P. lateromaculata Cook, sp. nov. are relatively widespread within Thailand and have overlapping distributions whereas P. melanodera Cook, sp. nov. appears restricted to small brackish ponds near western coastal areas of peninsular Thailand.


Introduction
The family Pleidae in Southeast Asia is represented only by species in the genus Paraplea. Paraplea areolata Paiva, 1918 was described from Myanmar (Burma,) and P. davaoensis Miyamota, 1981 andParaplea sobrina (Stål, 1860) are known from the Philippines. Two species, P. frontalis (Fieber, 1844) and P. liturata (Fieber, 1844) are likely widespread in Southeast Asia, and also occur outside this region. In Southeast Asia, P. frontalis and P. liturata have been recorded from Indonesia, Myanmar (Burma), West Malaysia, Singapore, Taiwan, and Thailand. Paraplea frontalis is also known from China, India, Sri Lanka, and Taiwan, and P. liturata from Australia, Japan, and New Caledonia. Paraplea vittifrons (Horváth, 1919) is known from the type specimen from the Aru Islands of Indonesia, which is in maritime Southeast Asia.
Members of the family Pleidae are rarely collected. These are very small aquatic bugs that are often overlooked in nature and collections, and they occur in habitats that are rarely sampled. The most common habitat where pleids occur is in slow moving or stagnant waters, with rich vegetation (Andersen and Weir 2004), although this may not be true for some regions, such as Thailand. Besides being overlooked and occurring in a habitat that is rarely collected, there has been little recent research emphasis on this family. Chen et al. (2006) recorded aquatic Hemiptera in Thailand, and identified P. frontalis and P. liturata in northeastern Thailand. Herein we report results of extensive collections throughout Thailand and describe two new species of Paraplea, as well as report the distribution of the species of Paraplea of Thailand.
The taxonomy of species in Pleidae is based primarily on a few key characters of uncertain taxonomic importance. Traditionally, genera could be identified solely on the index of their tarsal segments (Cook 2011). All known pleid species have three tarsal segments on their metathoracic leg. Species with two tarsal segments on their prothoracic and metathoracic legs are included in Paraplea, whereas those with two prothoracic tarsal segments and three mesothoracic tarsal segments are placed in Neoplea. Species with three tarsal segments on all legs are in Plea or Heteroplea, the latter having a callus posteriorly on the head. However, this classification may be artificial as there has been no phylogeny of the family. Other characters that appear to be valid for taxonomic purposes include the tooth pattern of the ovipositor (Sublett and Cook 2015), profile of the sternum, widths of the pronotum and scutellum, state of body sculpturing, male and female opercula, male parameres, and form of the clavus (Drake and Chapman 1953). Cook (2017) added indices of body shape, an ocular index, pronotal index, scutellar index and scutellar length index to the evaluation of species in Pleidae. The descriptions herein use all of these characters to delineate species.
The genus Paraplea is the most widespread genus in Pleidae with 19 valid species. Two species are from the New World, known primarily from the Caribbean and the southeastern United States; four species are from Africa; two from India; two from Australia; three from Japan or Taiwan; and six from Southeast Asia. With the addition of the two species from Thailand described in this study, this region is clearly the most diverse for Paraplea. However, there are likely many more species that remain unknown and await discovery and description.

Materials and methods
Most specimens for this study were field collected by co-authors Sites and Vitheepradit and their colleagues. Photographs of these collection sites, identified as L-numbers, are available in a Locality Image Database via a link from the internet site of the Enns Entomology Museum, University of Missouri. Other specimens were from previously collected materials deposited in the Snow Entomology Collection, University of Kansas (SEMC) and the United States National Museum (USNM). The recently collected specimens for this study are housed primarily in the Enns Entomology Museum, University of Missouri (UMC) and Sam Houston State University Natural History Collections (SHSU). Maps using data reported in the text were produced with SimpleMapper (Shorthouse 2010). Observations and measurements were made using an Olympus SZX16 microscope with an ocular micrometer and a Keyence VHX-6000 digital microscope. In total, 1279 adult specimens of Thai Pleidae were examined for this study, with 948 used for measurements due to their overall condition and orientation. Indices used for the description are:

BSI
Body Shape Index (body width/body length) x 100 OI Ocular Index (narrowest width between eyes/width of head across the eyes) x 100; width between eyes is taken anteriorly in dorsal view, width of head is at widest point including eyes PI Pronotal Index (length of pronotum/width of pronotum) x 100 SI Scutellar Index (scutellum width/scutellum length) x 100 Description of the ovipositor (gonapophyses) follows the terminology of Sublett and Cook (2015).

Results and discussion
Four species were found in Thailand, two previously described and two new. Although the two previously described species, P. frontalis and P. liturata, are relatively well known, they lack a complete modern description. Both were partially redescribed by Lundblad (1933) but not all meaningful taxonomic characters were addressed. All species of Paraplea found in Thailand are described below. Two species are new descriptions and two species are supplementary redescriptions.
Remarks. Paraplea frontalis was described as Ploa frontalis by Fieber (1844) for specimens collected in the East Indies. The original description was not extensive and relied heavily on coloration, which has proven to be a somewhat variable character in pleids. However, this description included a documentation of the distinctive markings of the face and vertex that is found in most specimens of this species. The figures provided with the original description are not very helpful in distinguishing P. frontalis from other pleid species. No types were designated by Fieber; however, the distinctive markings of the head made associations with subsequent collections possible with a relatively high degree of certainty. Kirkaldy (1898) reported on a specimen from Rangoon (now Yangon) in present day Myanmar (Burma), and in this and his later publication (Kirkaldy 1904), he followed Leach (1817) in putting all of Pleinae into the genus Plea, thus changing the name of this species to Plea frontalis. Kirkaldy (1904) also included a range extension of the species into Bengal, which is now in Bangladesh, although it is possible that he did not distinguish between West Bengal and East Bengal, leaving uncertainty to the exact region, which would now be in either India or Bangladesh, respectively. Kirkaldy also reported specimens from Pondicherry (India) and Cochin, China, which is now in Vietnam. Kirkaldy did not provide a description of the specimens he included in P. frontalis. Distant (1906) provided an English translation of the original description by Fieber but stated that he was unable to view any specimens of the species. Distant (1910) described a species from Calcutta and Madupur, West Bengal, India as Plea pelopea based primarily on coloration, including having a head with four dark spots and commented that he thought this could be an "extreme variety" of Plea pallescens. Plea (Paraplea) pelopea was considered by Lundblad (1933) to be the same as P. frontalis, although there was no type available for comparison. Lundblad (1933) determined that all previous treatments of P. frontalis did not allow for precise identifications. He commented on the most common head marking of having five dark markings and provided drawings of the head, antenna, legs, pronotum, sternal crest and parameres, but he did not provide a complete re-description. Lundblad (1933) also described a new species, Plea (Paraplea) quinquemaculata, which is now considered a synonym of P. frontalis (Nieser 2004). Benzie (1989) redescribed the species using specimens from Sri Lanka, including many of the characters used for modern descriptions in this family. Although all of these forms are now included as P. frontalis, it is possible that this represents a species complex. Below is a supplemental description of the species, based primarily on specimens from Thailand that fit within P. frontalis as it is currently defined.
Type information. No holotype is designated. Fieber (1844) reported that the description was made from specimens collected by Dr. Helfer in the East Indies, although the exact location in this region of Southeast Asia is not documented in the literature. A specimen of Pleidae collected by Dr. Helfer is deposited the National Museum in Prague (NMPC) that could give an indication about the area where the original P. frontalis was collected (Nico Nieser communication). This specimen could become a neotype if it is determined to be P. frontalis, however this specimen has not yet been evaluated.
Supplementary description. All measurements are given in millimeters from 456 adult specimens from throughout Thailand as reported in the distribution portion of this paper. Specimens used for this description are deposited at SEMC, SHSU, and UMC. Other specimens from Thailand and areas outside Thailand were surveyed but were not included in measurements due to condition or availability.
Color. Color may vary among individuals (Fig. 1A, D). Base color of body ranges from light brown to almost cream-colored, some with light honeycomb pattern, espe- cially on pronotum; punctures throughout body usually with dark center; scutellum usually golden-tan; legs light brown; sternum and venter darker brown; eyes red to golden to silver in dried specimens, dark blotches seen in various places on some specimens, distinctive dark spots on face and vertex (Fig. 1C).
Head. Head (Fig. 1C) generally light brown to cream colored with dark brown markings, mouthparts dark brown. Face and vertex normally with distinctive markings consisting of pair of spots near vertex, pair of spots between top margin of eyes and vertical line along midline of face, between middle of eyes; markings can differ between individuals; 64% with dark bar and four spots, 25% with light brown bar and four spots, 10% with light brown bar and two spots, 1% with either dark or light brown bar only (see Benzie 1989, Fig. 12 for diagram showing differences). Antenna three-segmented, usually hidden from view below eye. Head size similar among Thailand specimens, head width at widest point including eyes 0.92-1.04, head width at narrowest point between eyes, 0.47-0.56, OI 49-55.
Wings. Complete to posterior; punctures generally in irregular rows (0.02 in diameter) (Fig. 1A); underlying honeycomb structure sometimes present; claval suture distinct, complete; scutellum with distinct, dark punctures, more widely spaced than other punctures (Fig. 1B); scutellum base color often golden compared to tan base of hemelytra ( Fig. 1B), although sometimes both cream colored (Fig. 1D); yellowishbrown spot at terminal angles of corium often present as reported in original description, but not always readily apparent, posterior half rarely brownish as in original description; lateral view shows distinct dorsal horizontal shape and posterior near vertical aspects with a transition of nearly 90° (Fig. 1A, C); scutellum slightly wider than long ( Fig. 1B), scutellum length 0.46-0.57; scutellum width 0.54-0.66; SI 104-120. Hind wings membranous, fully developed, completely concealed by hemelytra.
Median ventral keel. Thoracic portions distinct from each other; prosternal keel rounded with posterior blunt tooth; mesothoracic keel almost rectangular; metathoracic keel irregularly shaped, somewhat in lobes, including posterior projecting small tooth, closely associated with abdominal keel, appearing almost fused; thoracic segments relatively similar between specimens. Abdominal keel variable, usually partially fused between segments, usually with four distinct teeth corresponding with first four  Fig. 2, but also see drawing by Lundblad (1933, fig. 44H).
Characters of female. Ovipositor roughly triangular in shape, 0.25 in length, with wide side apically (gonapophysis 1) at end of rectangular shaft (gonapophysis 2) (Fig. 3); six distinct teeth along posterior border (apical row) plus two teeth on ventral border (ventral 1 and 2), three rows of small teeth away from apex, two primary, three secondary, and usually three tertiary, although there is variation in number of tertiary teeth; one long hair on ventral side where triangular apex of gonapophysis 1 and basal rectangle of gonapophysis 2 meet. Subgenital plate as in Fig. 4; wider than long; width ~ 0.67, length ~ 0.41; faintly rugose in basal one third; tufts of relatively long hairs on each side near apex; short inconspicuous hairs throughout genital plate darker vshaped prominence in center, near apex.
Characters of male. Aedeagus bulbous and somewhat asymmetrical in the typical fashion of the family; operculum (subgenital plate) generally triangular, slightly wider than long (Fig. 5), width ~ 0.46, length ~ 0.41; lightly rugose throughout; with short hairs throughout.
Distribution. Paraplea frontalis is a relatively widespread species in Thailand (Fig. 24A) as well as other parts of Southeast Asia. This study adds the first records from Laos. Discussion. Because of the wide geographic distribution and variable characters, it is possible that what has previously been considered to be P. frontalis may include more than one species. Previously, it has not been possible to differentiate between species variation and species boundaries. However, after viewing hundreds of specimens, it appears that there are some reliable characters as long as there is a series of specimens in the sample to account for the variation. Lundblad (1933) noted that this is a species with variable characters, which is supported by the findings of this study. If a single specimen is used for identification, there may be some uncertainty in obtaining an accurate identification. The most apparent diagnostic character of P. frontalis is the facial marking found in most specimens, consisting of five dark marks, one vertical stripe on the center of the face and two pairs of horizontal stripes (Fig. 1C). Nearly 90% of specimens examined had these markings (although with variation in how dark these markings appear); thus, with a series of specimens, the species as now defined is readily identified. The current data did not include the type specimens (because they were never designated); however, they did match this diagnostic characteristic given in the original description. Paraplea brunni (Kirkaldy) and P. halei (Lundblad) also commonly have facial markings but they are usually restricted to the center vertical stripe and are not known to have the full component in the pattern shown in Fig. 1C. The scutellum in most specimens of P. frontalis is a contrasting lighter color and is often golden-orange. The keel of these specimens is also usually diagnostic, having well-defined teeth on the abdominal segments that are relatively longer than in other species, but there is variation in this character. Some specimens have smaller teeth, which could have resulted from wear, and the shape of these teeth can vary from being relatively straight to curved. The drawings of the keel by Lundblad (1933) of specimens from Indonesia had smaller teeth on the abdominal keel than did the majority of those examined in this study, but without examining the Indonesian specimens, it is uncertain if this is typical of specimens from these islands. As with most species of Pleidae, the ovipositor and subgenital plates of both sexes are diagnostic of the species. The ovipositor of P. frontalis most commonly has the teeth as shown in Fig. 3, but some specimens appear to be lacking inner teeth. This could be slight intraspecific variation or possibly interspecific differences if P. frontalis proves to be a species complex.

Paraplea lateromaculata
Description. All measurements are in millimeters and were taken from 224 adult specimens from throughout Thailand as reported in the distribution portion of this paper. Specimens used for this description are deposited at SEMC, SHSU, and UMC.
Body size. Total length, 1.21-1.58 (average 1.42) ( Fig. 6A, B, D); two specimens not included in this range unusually large, 2.35 and 2.52, but consistent in all other morphological characters with this species.
Color. Color may vary slightly among individuals ( Fig. 6A, B, D). Base color of body most often golden-tan with some darker brown markings. A few specimens exhibit a weak banding pattern of the hemelytra (Fig. 6A), banding more pronounced in small percentage of individuals that are more lightly colored (Fig. 6B); many with some honeycombing (Fig. 6B, D); small percentage of lightly colored specimens with red patches on vertex of head. Nearly all specimens with three dark spots on pronotum, two near posterolateral region and one at dorsal middle posterior. Distinctive dark spot on hemelytra above metacoxa (Fig. 6A, D).
Head. Head (Fig. 6C) generally light-brown to cream-colored, often with darker markings between eyes. Face and vertex often with a distinctive vertical bar (Fig. 6C), although sometimes missing or not distinctively bar-shaped. Antenna three-segmented, usually hidden from view below eye (extended and visible in Fig. 1A). Head size similar among Thai specimens, head width (excluding two unusually large specimens noted above) at widest point including eyes 0.62-074 (average 0.67), head width at narrowest point between eyes, 0.29-0.39 (average 0.35), OI 45-55 (average 50).
Pronotum. Base color usually light-tan but ranging between nearly white to brown, usually with lighter colored honeycombing apparent; most specimens have three distinct dark spots, one near posterolateral edge and one near the central posterior margin of pronotum ( Wings. Complete to posterior; punctures evenly dispersed with only small distance between punctures, not in rows (0.02 -0.03 in diameter) (Fig. 6A, D); underlying honeycomb structure sometimes present; claval suture present in most ( Fig. 6A) but absent in some (Fig. 6D); scutellum with distinct punctures, usually darkened in center ( Fig. 6B), more widely spaced than other punctures, punctures not in apparent order; scutellum base color similar to hemelytra, almost white to golden-brown; lateral view shows distinct black spot near margin (Fig. 6A, D), resembling spots on prothorax; darker vertical band on some specimens (Fig. 6B); shape of hemelytra ranging from rectangular (Fig. 6A) to having a dorsal bulge (Fig. 6D); scutellum slightly wider than long but often almost triangular (Fig. 6B), scutellum length 0.21 -0.43 (average 0.30); scutellum width 0.28-0.48 (average .36); SI 106-148 (average 120). Hind wings membranous, fully-developed, completely concealed by hemelytra.

Median ventral keel.
Thoracic portions distinct from each other, prosternal keel somewhat rectangular with small teeth at anterior and posterior edges; mesosternal keel small but distinctly squared in profile, slightly serrated; metathoracic keel segment somewhat rounded with prominent teeth. Abdominal keel on segments I-IV with distinct teeth, segment I appears fused to metathoracic keel. Figure of typical specimen in Fig. 8.
Characters of female. Ovipositor roughly rectangular but apical side slightly wider (gonapophysis 1) at end of fused rectangular shaft (gonapophysis 2) (Fig. 9); five distinct teeth along posterior border (apical row), although fourth tooth is smaller and somewhat recessed. In some specimens this small tooth appears to be missing; three teeth on ventral border, decreasing in size posteriorly; two rows of three teeth each away from apex, three primary and three secondary, but usually no tertiary teeth; one long hair on ventral side where triangular apex of gonapophysis 1 and basal rectangle of gonapophysis 2 meet, however this hair is sometimes inconspicuous except at high magnification; subgenital plate as in Fig. 10; slightly wider than long; width ~ 0.28, length ~ 0.25; relatively smooth but with hairs emerging from shallow pits; tufts of relatively long hairs on each side near apex; slightly shorter hairs spaced throughout genital plate darker v-shaped prominence in center, near apex and extending 2/3 to posterior border.

Characters of male.
Aedeagus bulbous and somewhat asymmetrical in typical fashion of family; operculum (subgenital plate) generally triangular, slightly longer than wide (Fig. 11), width ~ 0.23, length ~ 0.25, lightly rugulose in center before apex but otherwise smooth to granular, with short hairs throughout, several longer hairs at apex.
Distribution. Paraplea lateromaculata is found throughout most of peninsular Thailand, and few specimens have also been collected in eastern Thailand (Fig. 24B). Specimens observed include a single specimen collected from Singapore.   Etymology. The specific epithet combines two Latin roots, latero-meaning the side and -macula meaning spot. Thus, the name refers the distinct dark spot on the lateral side of the hemelytra. This spot is similar to the dorsal pronotal spots found in this species and P. liturata.
Discussion. In general appearance, P. lateromaculata sp. nov. could be misidentified as P. liturata that is missing two of its dark pronotal spots. However, several consistent characters separate these species. The most obvious of these characters is that P. lateromaculata sp. nov. has one dark spot on each side of the hemelytra, anteriorly near the costal margin, which is absent in P. frontalis. The ovipositors of these species are quite different (compare Fig. 3 with Fig. 9), and diagnostic characters of the ventral keel and genital plates also differ between these species. Paraplea lateromaculata sp. nov. is much smaller, none of which had body lengths reaching a length of 1.60 compared to the smallest measured P. frontalis at 1.89.
Paraplea lateromaculata sp. nov. can be differentiated from P. melanodera sp. nov. by their colored markings. More specifically, Paraplea lateromaculata sp. nov. has the distinctive black spots whereas P. melanodera sp. nov. has no black spots but has a black band at the posterior margin of the head. Although the size is similar between P. lateromaculata sp. nov. and P. melanodera sp. nov., recognizable differences exist in other characters as listed in their respective descriptions. Paraplea lateromaculata sp. nov. often has three pronotal black spots on the prothorax as is found in less than 10% of P. liturata; however, P. liturata has never been observed to have the black spots on the hemelytral costal margin as is seen in all specimens of P. lateromaculata sp. nov. Figures 12-17 Remarks. Paraplea liturata shares some of the same taxonomic history as P. frontalis since both were described in the same paper. Paraplea liturata was described as Ploa liturata by Fieber (1844) for specimens collected in the East Indies. This original description was not only brief but did not capture an important set of markings that is commonly present on specimens of P. liturata, even though the description relied almost completely on coloration. Fieber noted the typical two dashes between the eyes and the pair of lateral and single midline spots on the posterior margin of the pronotum. However, two spots on the anterior part of the pronotum were not listed in the description nor on his plate. The figure does show the hemelytral banding that is common in many specimens. Although types were not designated by Fieber, subsequent researchers were able to associate the description with many specimens of this common species, although none of these were those used by Fieber. Placement of this species into the genus Paraplea followed the same sequence as reported for P. frontalis. Kirkaldy (1904) moved this species into the genus Plea but made no comments on the species. Distant (1906) translated Fieber's description but did not further report on this species. Distant (1910) described Plea metiadusa from Calcutta, India and reported that it had no maculations, but this species was still determined to be a variant of P. liturata by Lundblad (1933). In doing so, Lundblad (1933) commented on the variability of the pronotal spots that are most commonly five in number but can range from none to seven. Distant (1914) also described Plea rufonotata but did not associate it with P. liturata. The description of P. rufonotata from New Caledonia was the first time that a pronotum with five spots was described, which now appears to be the most common state for P. liturata. Again, Lundblad (1933) made the association of these species as being synonyms. Horváth (1918) described Plea fasciata from specimens from Bata-via, Java (Indonesia) but this was considered a strongly-colored example of P. liturata (Lundblad 1933). Plea quinquenota (Paiva 1918) was described from a single specimen from Inlé Lake, Yawnghe State (now in Myanmar) and was not examined by Lundblad (1933), but was still synonymized with P. liturata based on the illustration of the new species perfectly matching the typical form of P. liturata. Along with the taxonomic clarifications, Lundblad (1933) also redescribed the species. Below is a supplemental description of the species, incorporating specimens from Thailand.

Paraplea liturata (Fieber, 1844)
Holotype. None designated. Type locality. Fieber (1844) reported that the description was made from specimens collected by Dr. Helfer in the East Indies but the exact location in South or Southeast Asia is unknown.
Supplementary description. All measurements are in millimeters and were taken from 221 adult specimens from throughout Thailand as reported in the distribution portion of this paper. Specimens used for this description are deposited at UMC and SHSU.
Body size. Total length, 1.27-1.68 (average 1.48) in Thailand specimens. Fieber (1844) reported total length of "approximately 2 mm." Distant (1910) gave the size of his later synonymized P. metiadusa from India and his later synonymized P. rufonotata from Caledonia as 2. The specimen used to describe the later synonymized P. quinquenotata was listed as 1.5 (Paiva 1918). Anderson and Weir (2004) reported a length of 1.8-2.0 for this species in their key and reported it from Northern Territory and Western Australia.
Color. Color may be quite variable among individuals within a population. Base color of body ranges from tan (Fig. 12A, B) to white (Fig. 12D). Darker bands on the sides of the hemelytra are common but not observed in all individuals. When present, bands are darker than the base color, ranging from light orange-brown (Fig. 12D) to tan (Fig. 12A) to brown (Fig. 12B). Punctures are sometimes a darker shade (Fig. 12A). Honeycombing matches the base color. Most specimens have five characteristic dark spots on the pronotum (Fig. 12B); two on the anteromedial portion ( Fig. 12 B), two on the posterolateral region (one on each side) (Fig. 12B, D), and one on the posteromedial region (Fig. 12B, D). Conversely, these spots are sometimes faint or absent in some individuals and at some locations.
Head. Head (Fig. 12C) colored with base body coloration, ranging from white to brown. Many specimens with a vertical light-colored bar between eyes. If present, bar can be thin (Fig. 12C) to wider, sometimes occupying nearly a third of width between eyes. Two dark spots common on face, one on each side between central bar and eyes (Fig. 12C). Eyes in dried specimens range from red to gold. Mouthparts usually darker that the rest of head. Antenna three-segmented, usually hidden from view below eye. Head size similar among Thailand specimens, head width at widest point including eyes 0.62-0.79 (average 0.72), head width at narrowest point between eyes, 0.31-0.43 (average 0.40), OI 47-58 (average 53). Pronotum (Fig. 12B). Base color ranging from white to light brown and honeycombing apparent in most specimens; most specimens with five dark spots on pronotum (91% of Thailand specimens with five spots, ~ 9% with three spots and lacking anterior pair, less than 1% with no spots); a shallow puncture in center of each cell of honeycomb and under high magnification a minute hair can usually be seen coming from each pore; with slight bulge posteriorly, wider than long, width 0.66-0.92 (average 0.79); pronotum length 0.33-0.57 (average 0.46); PI 39-68 (average 58).
Characters of female. Ovipositor most commonly as in Fig. 15. Ovipositor roughly rectangular in shape but with apical gonapophysis 1 slightly wider; five distinct teeth along posterior border (apical row) plus two teeth on ventral border (ventral 1 and 2); two rows of small teeth away from apex, three primary, three secondary, and occasionally one tertiary (not shown in Fig. 15); bottom secondary tooth larger and extends slightly beyond end of ovipositor, making it sometimes appear as being along posterior margin; three to five long hairs on ventral side of region where gonapophyses 1 and 2 Figures 13, 14. Paraplea liturata. 13 prothoracic leg above, mesothoracic leg in the middle and metathoracic leg below. 14 profile of the ventral keel with the anterior end (thoracic) to the top and ventral to the left.  meet; Subgenital plate slightly longer than wide (Fig. 16), length ~ 0.30, width ~ 0.26, lightly rugose in basal half followed apically by a series of pits, dark region in center near apex, pair of tufted hairs on each side near apex.
Characters of male. Aedeagus bulbous and somewhat asymmetrical in typical fashion of family; operculum (subgenital plate) as in Fig. 17, most of surface slightly rugose, longer than wide, length ~ 0.27, width ~ 0.20.

Distribution.
In Thailand, Paraplea liturata appears to be mostly a peninsular species on the southwest side of the country, although there are two records of it in the eastern region of Thailand; one in Sakon Nakhon Province, which was reported by Chen et al. (2006), and one by RWS and AV in a pond in Ubon Ratchathani Province (Fig. 24C). It is also known from Australia (Anderson and Weir 2004), India (Paiva 1918. Lundblad 1933, Indonesia (Lundblad 1933, Nieser andChen 1999), Malaysia (Fernando and Cheng 1974), Myanmar (Paiva 1918), New Caledonia (Lundblad 1933), Philippines (Lundblad 1933, Nieser andChen 1999), and Taiwan (Mitamura et al. 2018). Discussion. There is considerable variation in P. liturata if this is a single species. Lundblad (1933) mentioned this variation when synonymizing P. fasciata, P. metiadusa, P. quinquenotata, and P. rufonotata with P. liturata. The main basis for Lundblad synonymizing these species was the similarity of the abdominal keel. The drawings in his paper (Lundblad 1933) show similarities but there are also subtle variations. The Thailand specimens are also somewhat different from those in the Lundblad drawings. These data preserve the question as to whether this is a variable species or multiple species. Several of the species Lundblad synonymized had been described as having a length of 2 mm, although he stated that this was a small species varying between 1.3 to 1.7 mm. This size range of Lundblad's specimens coincides with that of specimens from Thailand; however, it still does not account for those described from India, New Caledonia, and Australia. The original description of P. liturata by Fieber (1844) listed the length imprecisely as "approximately 2 mm" and it is uncertain where in the East Indies these specimens were collected or how accurately that measurement was made. Likewise, some distinct differences in coloration and characters occur in specimens from the various regions.
A character that links all of these specimens into one species is the general state of having five spots on the pronotum. In many populations there can be specimens without these markings although the majority of specimens tend to always have five black pronotal spots. Thus, with a single specimen it may not be possible to rely on this trait but with a series of specimens it is easy to determine the species as P. liturata, as it is now defined. There appears to also be some consistency in the characters of the ovipositor. In many of the Thailand specimens, the ovipositor appears remarkably like that figured by Lundblad (1933: fig. 42H) from Java (Indonesia) which is consistent with the ovipositor being a reliable character for species recognition (see Sublett and Cook 2015); however, a small number of specimens lack some or all of the secondary and tertiary teeth. Since the ovipositors of specimens from India, New Caledonia and Australia are unknown, there is still a question as to if specimens from these regions are actually P. liturata. Like P. frontalis, P. liturata could be a species complex. Both these species need additional study to determine their status.
Ecology: The habitat of P. liturata in Thailand is typical for the majority of pleids. This species was often found in ponds, in shallow water with vegetation. Description. All measurements are in millimeters and were taken from 47 adult specimens from Thailand as reported in the distribution portion of this paper. Specimens used for this description are deposited at UMC and SHSU.

Paraplea melanodera
Body size. Total length, 1.28-1.66 (average=1.49) (Fig. 18A, B, D). Color. Color may vary slightly among individuals (Fig. 18A, D) but all specimens with a dark brown to black band at back of vertex of head. Base color of body usually light tan to golden-tan with some darker brown markings (Fig. 18A); although, some specimens have a base color almost white (Fig. 18C, D). A few specimens with weak banding pattern of hemelytra (Fig. 18A, C); honeycombing present but often sparse and difficult to see in some specimens.
Median ventral keel. Thoracic portions distinctively shaped but often hidden by enlarged coxa; prosternal keel broadly rounded, with irregular edges; mesosternal keel narrow, distinctive finger-like projection posteriorly; metathoracic keel segment somewhat rounded with prominent cleft towards center, sometimes appearing to almost overlap first abdominal section; abdominal keel I somewhat rectangular, with distinct tooth, abdominal keel II somewhat square, posterior tooth, abdominal keel III and IV shaped like posteriorly projecting teeth, IV longer than III (Fig. 20).
Characters of female. Ovipositor expanded apically (Fig. 21); five distinct teeth along posterior border (apical row), two large teeth in ventral half, three smaller teeth in dorsal half; three teeth on ventral margin, decreasing in size basally. Two rows of three teeth each away from apex, three primary and three secondary; most specimens with one tertiary tooth; several hairs along basal region of gonapophysis 1 that can be seen under high magnification. Subgenital plate triangular, slightly wider than long (Fig. 22), width ~ 0.42, length ~ 0.37; central anterior area of plate raised above other parts, with v-shaped sub-apical prominence; rugose in basal one third; central region towards apex mildly rugose; two distinct tufts of longer hairs on each side of center near apex; other single hairs present, especially toward apex.
Characters of male: Aedeagus bulbous and somewhat asymmetrical in the typical fashion of family; operculum (subgenital plate), longer than wide (Fig. 23); width ~ 0.29, length ~ 0.33, rugulose in basal one third but only lightly rugose anterior to that region; central finger-like projection in center towards apex; central region raised above marginal areas; long hairs clumped near apex, other single hairs throughout.
Distribution. Paraplea melanodera appears to be a species found only in peninsular Thailand along the west coast (Fig. 24D). Most of the known specimens are from ponds near the beach, thus it may be an endemic species to this region of Thailand.  Type material examined. Holotype: female, Thailand: Trang Province, Amphur Sikao, pond at Chao Mai Beach, 7°26.842'N, 99°20.647'E, 3 m, 9 I 2006, Vitheepradit and Prommi, L-907 (UMC Etymology. The specific epithet combines two Greek roots, melano-meaning black and -dero meaning the neck. Thus, the name refers the distinct dark line at the back of the head, which is distinctive of this species and a character not found in other members of the genus.
Discussion. The distinctive character of P. melanodera sp. nov. is the dark band at the posterior margin of the head. This character is seen in all specimens of this species and is not observed in any other species of Paraplea. Paraplea melanodera sp. nov. also has a raised central portion of the subgenital plate in both sexes and is most pronounced in the male. Other species of Paraplea in Southeast Asia do not have this character state. The coxae of P. melanodera sp. nov. are quite long. Paraplea lateromaculata sp. nov. also has long coxae, but are comparably shorter than those of P. melanodera sp. nov. Spines on the metathoracic femur are not common in Paraplea but are present in both P. melanodera sp. nov. and P. liturata. Paraplea melanodera also has spines on the prothoracic femur, including a couple that are longer than the others. Characters of the ventral keel, ovipositor, and subgenital plates also have distinct differences compared to other species of Paraplea.
In a study to determine the recovery of the lentic insect community following the Indian Ocean tsunami of 2004, Sites & Vitheepradit (2010) sampled ponds along the Thai coastline at four time intervals, including beginning five months after the tsunami, which marked the end of the dry season. Paraplea melanodera sp. nov. was collected in 11 of the 12 ponds inundated by the tsunami, including during the first sampling period, and in only two of the ten un-inundated reference ponds. The mean conductivity of all inundated ponds over all dates from which P. melanodera sp. nov. was collected was 1,714 μS, including one at 13,040 μS. Conductivity of the reference ponds further inland was < 100 μS and Indian Ocean seawater was over 41,000 μS. Thus, the waterbodies in which P. melanodera sp. nov. occurred had distinctly elevated levels of salinity. It is likely that P. melanodera sp. nov. also occurs further north and south along the coastlines to Burma and Malaysia.
Distribution of Paraplea in mainland Southeast Asia. Paraplea frontalis is one of the most widespread species of the genus and is prominent in Southeast Asia and beyond. In addition to the records reported here, P. frontalis has also been reported in other studies. Nieser (2004) stated that he had seen specimens of P. frontalis from Thailand, but these remain unpublished. The first published record of P. frontalis in Thailand did not appear until 2006 when it was reported from material collected in 1999 in Sakon Nakhon Province (Chen et al. 2006), which do not include those eluded to by Nieser (2004) (Nico Nieser pers. comm.). Lundblad (1933) described P. quinquemaculata (now a synonym of P. frontalis) from specimens from northern Sumatra. This region is directly west of mainland Malaysia and is considered maritime Southeast Asia, although with the short geographic distance across the Andaman Sea, it is not unexpected that these regions share species. Lundblad (1933) also reported two specimens of P. frontalis from Lake Toba, northern Sumatra and from East Java. Both of these specimens are in maritime Southeast Asia. Fernando (1961) collected P. frontalis (reported as P. quinquemaculata) at lights from Tanjong Karang, Selangor (Malaysia), which is close to the location of the Chapman specimens reported here. Fernando and Cheng (1974) mentioned that P. frontalis (reported as P. quinquemaculata) was collected once from a pond in Singapore but also stated that this species had never been collected in Malaya (Malaysia) even though Fernando (1961) had previously reported it from this region. Nieser and Chen (1999) reported on numerous collections of P. frontalis from Sulawesi and Sumatra (Indonesia). Esaki (1940) reported four specimens of P. frontalis from Chusan, which is an island off the southeastern coast of China. This region is not considered part of the political designation of Southeast Asia but is geographically close and this record would not be unusual with a mainland Southeast Asia species distribution. Esaki (1940) also stated that P. frontalis is widely distributed in India, Indochina, China, Java, Sumatra, Nicobar Islands and Formosa. However, no specimen data or source of that information was provided, nor did he mention any other Pleidae from this region. Esaki's distribution could include data from several species, or it might include undocumented distribution records for P. frontalis. Distant (1910) used specimens from Calcutta and Madhupur, India to describe Plea pelopea, which is now a synonym of P. frontalis. Hafiz and Pradhan (1947) also reported P. frontalis from the nearby locality of Patnagarh, India and further north at Gait Sarovar, Bolangir, India. These areas of India share many species with a mainland Southeast Asia distribution; thus, these records might not be considered unusual. Benzie (1989) found P. frontalis from waterholes in Yala National Park in southeastern Sri Lanka.
It is uncertain what factors influence the distribution of P. frontalis. The limited number of collections that represent our knowledge of this species suggest that it is most common in mainland Southeast Asia, but its distribution extends to the north into eastern Asia in China and Taiwan, west to India and Sri Lanka, and south to maritime Southeast Asia on islands of Indonesia. This paper represents the only data where an area was more thoroughly collected, although even this effort provides fewer than 500 specimens. When these collections are plotted on a distribution map (Fig. 24A), there is no perceptible indication of reasons for this distribution. In fact, with more collections, P. frontalis may be found throughout nearly all provinces of Thailand.
Another factor to consider is that what is reported as P. frontalis could be a species complex. This would not pertain to the distribution shown in Fig. 24A but could be a factor in reports in other areas of its distribution. There are noted morphological differences among specimens of P. frontalis from different parts of its range, including size differences, some differences in markings and other minor morphological variation. More study and many more specimens are needed to sort out this situation, probably including modern molecular comparisons of specimens from these various regions. Until this future study, P. frontalis will be considered a variable species with a wide distribution.
Paraplea liturata is widely distributed in Thailand and some predict that it could have the largest distribution of any species in the genus (Lundblad 1933, Fernando 1961. Its distribution in Thailand (Fig. 24C) does not appear as extensive of that of P. frontalis but it is a common inhabitant within a wide geographic distribution. Fernando and Cheng (1974) collected P. liturata at several locations in Malaysia and recorded it as being "fairly common" in this region. Nieser and Chen (1999) likewise found it in several locations in Indonesia as well as documenting the species in the Philippines.
Paraplea liturata does not appear to be restricted to any general habitat type or biogeographical region. Chen et al. (2006) stated that it was "common throughout Thailand in vegetation rich stagnant waters." The present study also indicates that the species occurs in ponds and slow-moving streams, both containing aquatic vegetation. Anderson and Weir (2004) reported P. liturata from Western Australia and the Australian Northern Territory, areas biogeographically quite different from Thailand and Malaysia, but did not comment on the specifics of the collection sites.
The distribution of P. lateromaculata sp. nov. (Fig. 24B) is very similar to that of P. liturata (Fig. 24C) in Thailand, including collection sites in common between these species. Both of these species were common in the peninsular region of Thailand.
The documented distribution of P. melanodera sp. nov. includes only the central part of peninsular Thailand (Fig. 24D). Even more restrictive is that it was collected only from small ponds near beaches along the coastline. The apparent halophilic nature of P. melanodera sp. nov. is well-documented because all specimens were collecting during the tsunami study of Sites & Vitheepradit (2010). The other three species of Paraplea also were collected during the study; however, these were mostly from uninundated reference ponds. More specifically, P. lateromaculata sp. nov. was collected in two reference ponds, including during all four sampling periods. Paraplea liturata was collected in all reference ponds over all sampling periods as well as a single individual from an inundated pond on the first sampling date, which we consider an adventitious occurrence. Paraplea frontalis was collected in two inundated ponds with elevated levels of salinity on the last sampling date, which was 17 months after the tsunami. Because eight and 28 specimens were collected in those two ponds, its occurrence was not adventitious; thus, P. frontalis appears to have a tolerance for salinity, but is not as adept at dispersing as is P. melanodera sp. nov.