Ptilomerella akekawati, Zettel, 2009

Zettel, H., 2009, Three new genera of Ptilomerinae (Hemiptera: Heteroptera: Gerridae) from Southeast Asia, Zootaxa 2046 (1), pp. 26-42 : 32-35

Ptilomerella akekawati sp. n.

( Figs. 8, 9 , 12–16, 18, 20, 22, 23)

Type material. Holotype (apterous male) labelled " Thailand: Phang-Nga Prov. \ SE Khao Lak, Tan Chong\ Pho Waterf., 26.11.\ 2006, leg. H. Zettel (35)" ( NHMW) . Paratypes (all apterous): 11 males, 12 females (including allotype), same label data ( NHMW, KUB, MUC, ZMUC, ZRCS) . 2 males, 1 female (apterous) "S Thailand, Phang-na Prov.,\ Tan Chongpa waterfall ne Khaolak \ 26 Nov 2006 YCM340\ CM Yang YCM340" ( ZRCS) . 1 male (apterous) " THAILAND: Surat Thani \ Khao Sok NP, N 08°54'\ E98°31', 30.11.–1.12.\ 2002, leg. F. Seyfert (15) " ( NHMW) ; 1 male (apterous) " THAILAND 2003\ PROV.SURATTHANI\ KHAO SOK N.P. 15.1.\ leg.: Horst FORSTER" ( NHMW) ; 1 male (apterous) " THAILAND: Phuket, Kathu \ District , forest streams &\ torrents (incl. wet rocks)\ 14.II.1989, Mogens Andersen\ Zool. Mus. Copenhagen" ( ZMUC) .

Type locality. Southern Thailand, Phang-Nga Province , southeast of Khao Lak, stream above Tan Chong Pho Waterfalls, in fast flowing sections of the stream above falls, between rock boulders .

Description. Genus characteristics are not repeated here.

Apterous male. Dimensions. Body length 6.3–7.2 mm (holotype: 7.1 mm). Maximum body width at mesoacetabula 2.1–2.5 mm (holotype: 2.3 mm). Head width 1.17–1.26 mm (holotype: 1.25 mm). Length of second antennomere of holotype 1.25 mm. Length of mesofemur 10.5–12.3 mm (holotype: 12.1 mm).

Colour. Body almost entirely pale yellowish brown ( Fig. 8 ). Head with vague, brown, V- or M-shaped mark. Pronotum with relatively broad, black lateral stripes which are posteriorly more or less extended ventrad towards coxal cavity. Acetabula with rather small, triangular, brown marks distally. Mesonotum with narrow dark margins anteriorly and posteriorly, usually with narrow, but distinct blackish midline (indistinct only in the specimen from Phuket, probably due to long storage in alcohol), separated from mesopleura by relatively broad, black line. Metanotum separated from metapleura by narrow line, with or without brownish midline. Acetabula with triangular brown marks. Metacetabulum with brown mark at base in addition. Metacoxa with blackish mark at base. Abdominal tergites 2–5 either entirely black or with sides light brown; tergite 6 light or variably infuscated; distal half of segment 8 and genitalia infuscated.

Structural characteristics (measurements refer to holotype). Relative lengths of antennomeres: 2.8: 1 (= 1.25 mm): 1.1: 0.6. Pronotum width 1.8 times median pronotum length. Lengths of leg segments relative to mesofemur: profemur 36, protibia 28, protarsus 9+5, mesofemur 100 (= 12.1 mm), mesotibia 62, mesotarsus 28+3, metafemur 105, metatibia 39, metatarsus 2. Profemur very slender, length 9.9 times maximum width near midlength. Metafemur slightly longer than metafemur (1.05 times), in some specimens with dense brush of hairs; brush about half of femur length leaving base and apex without pilosity; maximum hair length (at about midlength of femur) ca. 1.3 times mesofemur width; most specimens without such pilosity. Measured dorsally along midline, abdomen 0.7 times as long as thorax.

Paramere (Fig. 16) with acute hook, distal section S-curved, and relatively slender. Vesica sclerites (Fig. 18): recurved apical part of dorsal sclerite short and stout, at ventral curve with small process on right side; first lateral sclerites curved, widest at middle, with serrate distoventral margin; second ventral sclerites strongly asymmetrical, left one very small and close to apex of dorsal sclerite, right one long and slender, but weakly sclerotized.

Apterous female. Dimensions. Body length 6.8–7.6 mm (allotype: 7.0 mm). Maximum body width at mesoacetabula 2.1–2.7 mm (allotype: 2.4 mm). Head width 1.16–1.25 mm (allotype: 1.17 mm). Length of second antennomere of allotype 0.98 mm. Length of mesofemur 9.1–10.4 mm (allotype: 9.1 mm).

Colour as that of male. Proctiger dark brown.

Structural characteristics (measurements refer to allotype). Relative lengths of antennomeres: 2.8: 1 (= 0.98 mm): 1.2: 0.7. Pronotum width 2.0 times median pronotum length. Lengths of leg segments relative to mesofemur: profemur 38, protibia 29, protarsus 8+5, mesofemur 100 (= 9.1 mm), mesotibia 61, mesotarsus 29+4, metafemur 103, metatibia 41, metatarsus 2. Profemur slender, length 9.7 times maximum width near midlength. Metafemur hardly longer than metafemur (1.03 times). Measured dorsally along midline, abdomen 0.9 times as long as thorax. Connexiva posteriorly slightly folded over tergites, terminating in narrowly rounded or weakly acute angles (Figs. 20, 22). All tergites distinctly wider than long; tergite 1 slightly convex, matt; tergite 7 larger than preceding tergites, medially 1.4 times as long as tergite 6 (Fig. 22). Apex of abdomen high (Fig. 20). Sternite 7 with unique modifications, dorsolateral margin beset with dense, dark pilosity; distal section of sternite 7 with hind margin bearing dense, dark pilosity laterally, with small, medianly sharply (roof-like) folded medial lobe (Figs. 20, 23) bearing inconspicuous pilosity at hind margin.

Comparative notes. For specific differences, see notes at Ptilomerella anderseni sp. n. The long mesofemoral pilosity is developed in the four largest males (holotype and three paratypes), but completely absent from all other males. Because the genital structures are identical, this must be regarded as a intraspecific polymorphism. Within Ptilomerinae , such pilosity is only found here and in Ptilomera , but in Ptilomera it (almost) reaches the femoral apex and its development is highly species-specific (see, e.g., Polhemus and Polhemus 2001).

Distribution. Southern Thailand (Surat Thani, Phang-Nga, Phuket).

Habitat. Ptilomerella akekawati sp. n. was collected by the author in a small mountain stream. The section was above a waterfall and strongly structured by large rock boulders. Ptilomerella akekawati sp. n. was found only in small, extremely lotic places. There it was difficult to see because of its camouflage: the speedily moving specimens with their silvery patches were hardly discernable between the reflections of the waving water. Several specimens were caught by moving the net tentatively over the water surface of such places without seeing them. The same area of the stream was inhabited by Ptilomera kra Vitheepradit and Sites, 2007 , but both adults and nymphs of that species preferred less turbulent microhabitats.

Etymology. This species is named in honour of Akekawat Vitheepradit (Kasetsart University, Bangkok) to acknowledge his numerous contributions to a better knowledge of Thai water bugs. The epithet is a noun in the genitive case.

Figures

FIGURES 8–9. Ptilomerella gen. n. (8, 9) P. akekawati sp. n. (8) Habitus of apterous male (paratype; body length 6.3 mm), dorsal aspect. (9) Habitus of apterous female (paratype; body length 7.2 mm), dorsal aspect. © NHMW Hemiptera Image Collection, published with permission.