Hydraena essentia, Perkins, 2011

Perkins, Philip D., 2011, New species (130) of the hyperdiverse aquatic beetle genus Hydraena Kugelann from Papua New Guinea, and a preliminary analysis of areas of endemism (Coleoptera: Hydraenidae) 2944, Zootaxa 2944 (1), pp. 1-417 : 24-25

Hydraena essentia , new species

( Figs. 18 , 20, 434 )

Type Material. Holotype (male): Eastern Highlands Province: Sepik River Basin , stream beside milestone labelled G-99, unshaded stream with angular boulders, some coated with java moss, 1540 m, 6° 18' S, 145° 55' E, 1 vii–30 viii 1988, D. Dudgeon ( NMW) . Paratypes (12): Eastern Highlands Province: Same data as holotype (7 NMW) ; Gulf Province: Marawaka, Mala, 1400 m, 7° 5.664' S, 145° 44.467' E, 11 xi 2006, Balke & Kinibel ( PNG 90) (5 MCZ, NHM, NMW, PNG, ZSM) .

Differential Diagnosis. Quite similar in dorsal habitus to H. ambripes and H. sagatai ( Figs. 11 , 15 , 18 ); differing from both species by the more coarsely punctate dorsum and deeper pronotal foveae; additionally differing from H. ambripes by the smaller size (ca. 1.64 vs. 1.76 mm), and the differently shaped male metatibiae. Males of all three species have modified protibiae, those of H. essentia being the most strongly modified. The aedeagus of H. essentia is most similar to that of H. sagatai , but the two consistently differ in significant details, especially in the greatly reduced state of H. essentia ( Figs. 17 , 20).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.64/0.69; head 0.25/0.34; pronotum 0.34/0.46, PA 0.37, PB 0.35; elytra 1.04/0.69. Dorsum amber colored, head bicolored, frons darker than clypeus and labrum, legs light brown, maxillary palpi testaceous.

Frons punctures ca. 1xef; interstices shining, 1–3xpd. Clypeus microreticulate laterally, very finely sparsely punctate medially. Mentum very sparsely very finely punctate, shining; postmentum very finely densely micropunctulate in median concavity, surrounding areas smooth, shining. Genae raised, shining, without posterior ridge. Pronotum cordiform, anterior margin emarginate; lateral margins turning outward very slightly, if at all, at posterior angles; punctures on disc ca. 1–2xpd those of frons, interstices shining, 1–2xpd, punctures denser at anterior; PF1 narrowly separated one from the other by very low ridge (no present in all specimens); PF2 deep, oval, oblique, not confluent; PF3 and PF4 moderately deep.

Elytra distinctively humped just behind midlength, at summit of posterior declivity; lateral margins evenly arcuate; on basal 1/3 punctures ca. 1xpd largest pronotal punctures, punctures becoming gradually smaller toward posterior. Intervals not raised, shining, on disc ca. 1–2xpd, as are interstices between punctures of a row. Apices in dorsal aspect very weakly separately rounded, in posterior aspect margins forming shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 3/1.5/6/4. P1 narrow, not laminate; median carina sinuate in profile. P2 raised, l/w ca. 2/1, sides slightly converging toward apex, apex joined to raised mesoventral intercoxal process. Plaques narrow, slightly arcuate, slightly converging toward one another anteriorly, weakly raised, located at sides of deep, median depression. Metaventrite with strong midlongitudinal ridge between mesoventral intercoxal process and median depression, also with short longitudinal ridge on each side, extended posteriorly from margin of each mesocoxal cavity. AIS width at straight posterior margin ca. 1.5x P2. Profemur (male) with small, sharply pointed tubercle next to trochanter; protibia markedly emarginate on medial surface in distal 1/2. Meso- and metatibiae very slender, straight. Abdominal apex symmetrical.

Etymology. Named in reference to the markedly reduced aedeagus.

Distribution. Currently known from two localities near the eastern limit of Area 1; elevations 1400 m and 1540 m ( Fig. 434 ).

Figures

FIGURE 11. Hydraena ambripes, holotype, dorsal and lateral habitus, and venter.

FIGURE 15. Hydraena sagatai, holotype, dorsal and lateral habitus, and venter.

FIGURE 18. Hydraena essentia, holotype, dorsal and lateral habitus, and venter.

FIGURES 431–434. Geographical distributions of Hydraena species.

FIGURES 16–17. Aedeagi of holotypes. 16. H. ambroides. 17. H. sagatai.