Prohydrometra johnpolhemi D. Polhemus, 2022

Polhemus, Dan A., 2022, Two new genera and six new species of Terrestrial Hydrometridae (Hemiptera: Heteroptera) from French Polynesia, Zootaxa 5190 (1), pp. 69-98 : 81-82

Prohydrometra johnpolhemi D. Polhemus n. sp.

Figs. 11 , 16–18 , 24

Apterous male. Length 4.15, width 0.48.

Color. Ground color brown; abdominal mediotergites light-brown, matte. Head tinged with blackish. Thorax anteriorly light colored dorsally, tinged with dark-brown elsewhere; abdominal mediotergites IV–VI light medially; each laterotergite with light area anteriorly. Venter of thorax and abdomen light-brown. Legs light-brown, antennae light-brown to brown; coxae and trochanters mostly light-brown.

Structure. Head somewhat short for genus (1.45), widest at antenniferous tubercles (0.35); set with bristly setae beneath; gular lobe large, rounded; labium reaching well caudad of eyes, onto prosternum; head with anteocular portion slightly longer than postocular portion, ratio of anteocular/postocular portions: 0.80/0.60; interocular space/ width of an eye: 0.13/0.10; anteclypeus small, broadly rounded anteriorly. Antennae with lengths of antennomeres I:II:III:IV = 0.20: 0.28: 1.80: 1.18 ( Fig. 11 ). Pronotum length 0.55; remainder of thorax 0.30 (to lateral suture behind metacetabulae); abdomen length 1.65. Wing pads, if present, very small, not visible, hidden under pronotum. Thoracic and abdominal sterna with short bristly setae, about equally dense on all segments. Distance between anterior and middle coxae (measured between closest margins) 0.10; between middle and hind coxae 0.17.Acetabula without pits. Venter without black denticles.

Proportions of legs as follows: Femur, tibia, tarsomere I, tarsomere II, tarsomere III of fore-leg, 1.45: 1.68: 0.05: 0.10: 0.12; of middle-leg, 1.50: 1.78: 0.05: 0.10: 0.15; of hind-leg, 2.15: 2.56: 0.05: 0.12: 0.18.

First abdominal segment short, transverse, clearly delineated by a suture posteriorly. Mediotergites I and VII almost quadrate, others slightly longer than wide. Male abdominal sternum VII with two small, widely separated, triangular patches of bristle-like setae, directed ventrally, not close to anterior margin ( Fig. 24 ); segment VIII cylindrical, unmodified, without distal process.

Micropterous female. Length 4.30, width across abdomen 0.65. Similar in most respects to male, but abdomen broader, deeper, segment VII slightly curved upward, tergum VIII distally truncate, without distal process; margins of laterotergites without setae. Abdominal terminalia simple, without modification.

Brachypterous form and macropterous form: Unknown.

Type material examined (all micropterous). Holotype, male: FRENCH POLYNESIA, Society Islands , Raiatea , east coast, Mitimitiaute River at "Trois Cascades" area, inland from Vairahi Bay, on wet bedrock faces flanking second cascade, 200 m, 16°46'27"S, 151°26'35"W, 11 September 2007, 13:00-16:30 hrs., CL 7521, D. A. Polhemus & J. T . Polhemus ( BPBM). Paratypes: FRENCH POLYNESIA, Society Islands , Raiatea, 2 males, 4 females, same data as holotype, CL 7521 ( BPBM, USNM) .

Distribution. French Polynesia, Society Islands, endemic to the island of Raiatea ( Fig. 18 ).

Etymology. Named for the late Dr. John T. Polhemus, an indefatigable field collector, who discovered the first specimens of this species on a rheocrene adjacent to the second fall at Trois Cascade ( Fig. 17 ).

Discussion. This is the smallest known species of Prohydrometra , and the only one known to have a semiaquatic ecology. The male of P. johnpolhemi differs from all other species of the genus by the modification of male abdominal ventrite VII, which possesses two small, widely separated, barely curved, sclerotized processes displaced from the anterior margin ( Fig. 24 ). Although P. gagnei from Tahiti and P. moorea from Moorea also have ventrallydirected, spine-like processes on sternum VII, the processes in these latter species are larger, curved, and arise near the anterior margin of the ventrite (compare Figs. 19–21 with Fig. 24 ).

Ecological notes. This species was found on hygropetric habitats in the gorge of the Mitimitiaute River on Raiatea. Prior to this discovery, hydrometrids had not been recorded from Raiaeta, or anywhere else in the western Society Islands. Subsequent analysis of collections made in upland cloud forest habitats on Mt. Toomaru by Dr. Ron Englund revealed the presence of a terrestial Prohydrometra species on Raiatea as well. These results suggest additional Prohydrometra species might be present in isolated cloud forest patches near the summits of Bora Bora, Tahaa, or Huahine islands.

The type series of P. johnpolhemi was taken from wet bedrock walls adjacent to the second waterfall in a series of three ( Figs. 16, 17 ). Individuals occurred on wet basalt bedrock, but only in those areas without large amounts of moss or sheeting flow. The immatures formed aggregations, and were orange in color when alive. This is the only species of Prohydrometra known to inhabit a semi-aquatic habitat, with all others being arboreal inhabitats of moss-covered trees in upland cloud forests. As such, the ecology of this species is an anomaly within this insular radiation.

Figures

FIGURE 11. Prohydrometra johnpolhemi n. sp., head in lateral view, showing very long antennal segment III diagnostic for this genus. Specimen from French Polynesia, Raiatea, Trois Cascade, CL 7521.

FIGURE 18. Distribution of Prohydrometra species in the western Society Islands. Triangle = P. johnpolhemi n. sp.; square = P. englundi n. sp.

FIGURES 16, 17. Photographs of habitat for Prohydrometra johnpolhemi n. sp. at Trois Cascade, Raiatea, CL 7521. 12. Second waterfall, flanked by wet rock faces on which the species occurred. 13. Dr. John T. Polhemus collecting specimens on wet rock faces lateral to the waterfall.

FIGURES 19–24. Prohydrometra n. gen. species, male ventral terminal abdomen. 19. P. gagnei, specimen from Tahiti, Mt. Marau. 20. P. gagnei, specimen from Tahiti, Mt. Mauru, showing yellowish-brown coloration. 21. P. moorea n. sp., specimen from Moorea, Mt. Tohiea. 22. P. teatara n. sp., specimen from Tahiti, Mts. Teatara. 23. P. tohiea n. sp., holotype, specimen from Moorea, Mt. Tohiea. 24. P. johnpolhemi n. sp., specimen from Raiatea, Trois Cascade.