Hydraena thumbelina, 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 : 29-30

Hydraena thumbelina , new species

( Figs. 27 , 29 , 442 )

Type Material. Holotype (male): Madang Province: Finisterre Mts., Naho River Valley, Damanti , ex gravel banks of very fast-running clear stream, elev. 914 m, 5° 55' S, 145° 58' E, 11 x 1964, M. E. Bacchus (MEB 47) ( NHM) . Paratypes (34): Central Province: Kokoda , under stones, river side, elev. 365 m, 8° 39' S, 147° 15' E, 1–30 viii 1933, L. E. Cheesman (577) (3 NHM) ; nr. Port Moresby, Sogeri Plateau, Musgrave River , ex dead leaves caught among rocks, elev. [est.] 100–200 m, 9° 46' S, 147° 41' E, 16 iii 1965, M. E. Bacchus (MEB 200b) (1 NHM) ; Madang Province: Finisterre Mts., Naho River Valley, Budemu-Kikipei track, ex gravel banks of small stream, elev. 1220 m, 5° 56' S, 146° 40' E, 24 x 1964, M. E. Bacchus (MEB 74) (1 NHM) ; Finisterre Mts., Naho River Valley, Damanti , ex gravel bank of shallow stream, elev. 1082 m, 5° 55' S, 145° 58' E, 12 x 1964, M. E. Bacchus (MEB 49) (7 NHM) ; Finisterre Mts., Naho River Valley, Damanti , ex gravel banks of very fast-running clear stream, elev. 914 m, 5° 55' S, 145° 58' E, 11 x 1964, M. E. Bacchus (MEB 47) (9 NHM) ; Morobe Province: Herzog Mts., Vagau [Wagau], ex gravel banks of small clear river in dense forest, elev. 1220 m, 6° 48' S, 146° 48' E, 6 i 1965, M. E. Bacchus (MEB 140a) (2 NHM) ; Herzog Mts., Vagau [Wagau], ex muddy gravel banks of shallow clear swift river, elev. 1220 m, 6° 48' S, 146° 48' E, 9 i 1965, M. E. Bacchus (MEB 147b) (11 NHM) .

Differential Diagnosis. Very similar to H. thumbelipes in habitus, size, and shape of the male protibia ( Figs. 27 , 30 ). The shapes of the male metatibiae differ in the two species: in H. thumbelipes the metatibia is expanded subapically (SEM Fig. 291 ), whereas in H. thumbelina the metatibia is weakly sinuate on the medial margin ( Fig. 27 ). Reliable determinations will also be based on close examination of the quite similar male genitalia ( Figs. 29 , 32 ).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.40/0.53; head 0.24/0.33; pronotum 0.33/0.43, PA 0.36, PB 0.35; elytra 0.83/0.53. Dorsum of head piceous; pronotum brown in front of and behind piceous fascia, ratios of color bands, as measured in midline, ca. 4/15/4; elytra brown; legs and maxillary palpi light brown to testaceous, tip of palpus not darker.

Frons punctures ca. 1–2xef, slightly larger near eyes than medially; interstices shining, 1–4xpd. Clypeus microreticulate laterally, very finely sparsely punctate medially. Mentum very sparsely very finely punctulate, shining; postmentum micropunctulate. Genae raised, shining, without posterior ridge. Pronotum cordiform, median 1/2 of anterior margin emarginate; punctures on disc ca. 1xpd those of frons, interstices shining, 1–4xpd, punctures slightly larger and denser at anterior and posterior; PF1 absent; PF2 very shallow, obsolete; PF3 deep; PF4 absent.

Elytra with summit of posterior declivity at or very near midlength; lateral explanate margins moderately wide; 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, a few punctures subserial. Apices in dorsal aspect 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. 3/2.5/8/1. P1 laminate; median carina sinuate in profile. P2 raised, l/w ca. 2/1, sides converging toward blunt apex. Plaques large, very narrowly separated, more narrowly so at posterior than at anterior, weakly raised, each plaque tapering from posterior to anterior. Metaventrite without midlongitudinal ridge. AIS width at straight posterior margin slightly greater than P2. All legs moderately long and slender. Profemur (male) with tubercle next to trochanter; protibia slightly arcuate, medial margin widened in distal 1/3, apex with cluster of short spines. Mesotibia straight. Metatibia distal 2/3 emarginate on medial margin. Abdominal apex symmetrical, densely setose, penultimate tergite and ventrite fused; last tergite (male) notched. Aedeagus as illustrated ( Fig. 29 ).

Etymology. Named after the character of the childrens' book, who was shrunk to a very small size. Named in reference to the small body size of this species, and to the prominent cluster of spiniform setae that form a "thumb" near the apex of the male protibia.

Distribution. A moderately wide distribution in eastern PNG, found in Areas 5–7, and 11; elevation range 100–1220 m ( Fig. 442 ).

Figures

FIGURE 27. Hydraena thumbelina, holotype, dorsal and lateral habitus, and venter.

FIGURE 30. Hydraena thumbelipes, holotype, dorsal and lateral habitus, and venter.

FIGURES 28–29. Aedeagi of holotypes. 28. H. sepikramuensis. 29. H. thumbelina.

FIGURES 439–442. Geographical distributions of Hydraena species.

FIGURES 286–291. Scanning electron micrographs of H. thumbelipes.

FIGURES 32–33. Aedeagi of holotypes. 32. H. thumbelipes. 33. H. phainops.