Nereivelia polhemorum, Man & Murphy, 2011

Man, Yang Chang & Murphy, Dennis H., 2011, Guide To The Aquatic Heteroptera Of Singapore And Peninsular Malaysia. 6. Mesoveliidae, With Description Of A New Nereivelia Species From Singapore, Raffles Bulletin of Zoology 59 (1), pp. 53-60 : 56-58

Nereivelia polhemorum , new species

( Figs. 4 , 10–16 )

Material examined. – All specimens apterous. Holotype and allotype: Singapore, Mandai mangroves, under wet wood on intertidal muddy ground at 2.3 m above chart datum. 20 Mar. 1992, coll. D. H. Murphy ( ZRC) .

Paratypes: SINGAPORE: 4 males, same data as holotype; 2 males, 1 female, Sungei Buloh East mangroves, under imbedded timber on very wet muddy ground 2.4m above marine datum (above mean HWN) in air filled cavities, along with abundant Collembola ( Axelsonia and Dicranocentrus ), 22 Mar. 1992, coll. D.H. Murphy; 1 female, Sungei Buloh East mangroves, on lobster mound surface, 2.6m above marine datum, 1 Mar. 1991, coll. D. H. Murphy; 1 female, Sungei Buloh mangroves, on lobster mound surface, 22

Mar. 1992, coll. D. H. Murphy; 1 male, 1 female, Sungei Buloh mangroves, 12 Apr. 1999, coll. D. H. Murphy ( ZRC, NHMW, BPBM) .

Size. – males 1.70–1.85 (holotype 1.80, width 0.69); females 1.90–2.09 (allotype 2.03, width 0.81).

Description of holotype. – Body dark brown, lighter brown on legs and antenna, darker on thorax. Body elongate oval, covered with fine and coarse semi-erect hairs, denser on abdomen ( Fig. 10 ).

Head moderately sub-quadrate; matte, broadly rounded anterior and strongly deflected. Head almost as long as width across eyes (0.39:0.38). Interocular space 0.21. Three equally spaced trichobothria present. A longitudinal row of pits present on vertex, diverging dorsally and meeting at posterior margin of head; some small shining disc-like plates present near interocular space. Eye normal, large, spherical with about 24 ommatidia, and two long and curved ocular setae. Ocelli absent. Venter of head with a broad, raised, ridged plate, widening posteriorly, demarcated by a very low longitudinal carina on each side ( Fig. 11 ). Rostrum extending beyond hind coxa, length of segments III:IV, 0.67:0.18. Antenna long, slender and flagelliform, slightly shorter than body length (1.71:1.80). Segments I and II thick, without spines, III and IV much longer, flagelliform with long setae; segment II shortest. Length of antenna segments I–IV, 0.32:0.18:0.58:0.63.

Thorax length along midline subequal to head length (0.41:0.39), matte, lateral margins rounded. Dorsal margins with groups of small shining disc-like plates ( Figs. 12, 13 ). Pronotum longest on midline, slightly longer than combined length of meso- and metanotum which are almost subequal in length (0.22:0.10:0.09). Posterior margins of pro- and mesonotum straight, that of metanotum curved in middle. Greatest width of thorax (metanotum) slightly narrower than greatest abdomen width (0.65:0.69). Legs slender, covered with setae, without spines. Hind leg longest. Fore femur slightly more incrassate than other femora. Tibiae slender, equal or subequal length to fore- and mid-femur. Hind tibia longest. Tarsi with three segments, tarsal III almost 2 times the length of tarsal I; all tarsi bearing two equal terminal claws.

Measurements of legs of holotype Abdomen broad, shining, covered with dense and long semi-erect setae. Mediotergites tapering in width towards the abdominal apex. Tergite I more shining and with less setae. Tergites II–IV same length, tergite V shortest, tergite VII longest. Length of tergites I–VII, 0.07:0.09:0.09:0.09:0.06:0.08:0.23. Scent orifice distinct, located slightly behind middle on tergite IV ( Fig. 12 ). Laterotergites broad and slightly raised. Laterotergite IV broadest (0.13).

Genital segments relatively large and distinctly protruding from the pregenital abdomen. Longer than width (0.30:0.27). Posterior margin of segment VIII concave. Pygophore subovate, proctiger rectangular. Paramere small and symmetrical curved dorsally with pointed apex ( Fig. 14 ).

Description of allotype. – Similar in structure to male. Head length, 0.46; width across eyes, 0.43; Length of antenna segments I–IV, 0.30:0.18:0.60:0.64. Thorax shorter in length to head (0.38:0.46). Pronotum length greater than combined length of meso- and metanotum, 0.21:0.090:0.083. Body width gradually increase from thorax (max. width: 0.72) to abdomen tergite V (width 0.81) and tapering toward the tip of abdomen ( Fig. 4 ).

Measurements of legs of allotype Abdomen broad, length 1.18, tergite I shortest, tergite II equal in length to tergite VI, tergites III–V same length, tergite VIII longest. Length of tergites I–VIII, 0.09:0.12:0.10:0.10:0.10:0.12:0.15:0.19. Laterotergites broad, slightly raised. Genital segments relatively large. First gonocoxa large, gonoplac and proctiger small ( Fig. 15 ). Ovipositor large, gonapophyses elongate with strongly serrated teeth ( Fig. 16 ).

Macropterous form unknown.

Distribution. – Currently known only from the mangroves in Sungei Buloh and Mandai in Singapore.

Etymology. – The specific epithet dedicates this species jointly to father and son, John T. and Dan A. Polhemus whose generous guidance have been invaluable in our work with the aquatic Heteroptera.

Ecology. – Nereivelia polhemorum was found in the same habitat as the N. murphyi Polhemus & Polhemus , mostly under decayed logs on the intertidal zone of mangroves. They shelter in the air filled cavities of the dead wood during high tide and emerge during low tide to feed on small arthropods (Murphy pers. obs.). Nereivelia is now very rare in Singapore; several efforts have been made to obtain more material but failed. This is because of the “International Coastal Cleanup Program” of clearing “unsightly” timber and polyethylene bags from the mangroves since 1997 (Ng & Sivasothi, 1999), which effectively removed the air filled cavities which are inhabited by many enigmatic arthropods.

Remarks. – Nereivelia polhemorum shares the same characters with Austrovelia queenslandica Malipatil & Monteith , by having the scent orifice opening behind the middle of mediotergite IV, and by the absence of a longitudinal sulcus on the abdominal pleura (see tables by Polhemus & Polhemus, 1989 and Andersen & Polhemus, 2003). However, Austrovelia differs from the former in the distinctive dorsally swollen abdomen and the body size. We have examined paratypes of A. queenslandica and listed their characters for separating the two genera in Table 1. Our new species of Nereivelia resembles the type species, N. murphyi , by its body size and shape. It can be distinguished by the thorax having lesser and shorter setae and shining disc-like plates, by the scent gland orifice situated slightly behind middle of mediotergite IV, and by the concave posterior margin of male abdominal segment VIII. Other differences between the two species are summarised in Table 1.

Figures

Fig. 4. Nereivelia polhemorum, new species, apterous female, dorsal view.

Fig. 10–13. Nereivelia polhemorum, new species. 10. apterous male, dorsal view; 11. lateroventral view of head showing the longitudinal carina and the raised ridged plate; 12. dorsal view of abdomen and thorax, showing disk-like plates (D) and the scent orifice (S); 13. surface of thorax showing disc-like plates.

Fig. 14–16. Nereivelia polhemorum, new species. 14. male abdominal terminalia, lateral view showing paramere (P), proctiger (Pr), pygophore (Py); 15. Female abdominal terminalia, lateral view showing gonocoxa 1 (Gx1), gonocoxa 2 (Gx2), gonoplac (Gp), proctiger (Pr) and gonapophyses (Go); 16. Ovipositor. Scale bars: 0.1 mm.