Oosternum latum, Hebauer, Martin Fiká Č Ek Franz & Hansen, Michael, 2009

Hebauer, Martin Fiká Č Ek Franz & Hansen, Michael, 2009, Taxonomic revision of New World species of the genus Oosternum Sharp (Coleoptera: Hydrophilidae: Sphaeridiinae) I. Definition of species groups and revision of the Oosternum aequinoctiale group, Zootaxa 2054, pp. 1-37 : 34-35

Oosternum latum sp. n.

( Figs. 35 , 41, 45, 54–55, 63, 69, 75, 78, 84)

Type locality: Saint Vincent and the Grenadines (Windward Islands), Saint Vincent island.

Type material: Holotype. male ( BMNH): “ St. Vincent / W.I. / H. H. Smith / 6”. Paratypes (18). SAINT VINCENT AND THE GRENADINES: 1 male, 2 unsexed specimens ( BMNH, NMPC): same data as holotype; 2 unsexed specimens ( BMNH): “ St. Vincent / W. I. / H. H. Smith / 263.”; 5 unsexed specimens ( BMNH, NMPC): “ St. Vincent / W. I. / H. H. Smith / 47.”; 1 unsexed specimen ( NMPC): “ St. Vincent / W. I. / H. H. Smith / 41.”; 1 unsexed specimen ( BMNH): “41. [refers most probably to same locality as in previous specimen]”; 1 unsexed specimen ( BMNH): “Leeward side / St. Vincent W. I. / H. H. Smith / 34.”; 1 unsexed specimen ( BMNH): “Windward side / St. Vincent, W. I. / H. H. Smith”; 1 unsexed specimen ( KSEM): “12. / Windward side / St. Vincent, W. I. / H. H. Smith”; 2 unsexed specimens ( BMNH. KSEM): “ St. Vincent / H. H. Smith / 99-37”.

Differential diagnosis. Body widest at junction of pronotum and elytra; pronotum highly convex; pronotal punctation moderately dense, consisting of minute punctures; pronotal interstices with microsculpture; median carina of prosternum with anterior tooth; preepisternal elevation of mesothorax 2.0× longer than wide; median portion of metaventrite without intersticial microsculpture; eyes large, separated by 5.0× of one eye; parameres with moderately large inner projections; lateral projections of median lobe wide, developed in apical 0.3 of median lobe.

The species is easily recognizable by wide body-shape, body widest at junction of pronotum and elytra ( Figs. 35 , 41) and microsculptured pronotum (Figs. 54–55). By the combination of the mentioned characters it differs from all remaining species of O. aequinoctiale species group. It is also unique by prosternal carina producing into small tooth anteriorly (this character is best seen in lateral view, Fig. 78 ).

Description. HABITUS: Body widely oval, widest on base of elytra, highly convex in lateral view, strongly narrowing posteriad; TL/TW ratio = 1.5. Length: 1.20–1.50 mm, length of HT: 1.35 mm; width: 0.80–0.95 mm, width of HT: 0.85 mm.

COLORATION. Coloration of dorsal side reddish brown. Ventral side rusty brown, ventral surface of head reddish, epipleuron yellow. Femora, tibiae and antennal club pale reddish brown, tarsi and antennomeres 1–6 yellowish.

HEAD. Clypeus with moderately dense punctation, consisting of minute, nearly indistinct punctures, lacking setae; interstices with fine microsculpture; anterior margin slightly concave. Frons with moderately dense punctation, consisting of minute, indistinct setiferous punctures, punctures of same shape medially and laterally; interstices with fine mesh-like microsculpture. Eyes moderately large, separated by 6.0× of width of one eye. Mentum 2.8× wider than long, anterior margin deeply emarginate; punctation consisting of minute, nearly indistinct punctures bearing minute setae; interstices with very fine microsculpture, opaque. Submentum with poriferous disc-like fields. Maxillary palpus palpomere 4 ca. 1.3× longer than palpomeres 2 and 3. Scapus ca. as long as antennomeres 2–6 combined; antennal club ca. 2× longer than wide.

PROTHORAX. Pronotum apparently more convex than elytra, punctation consisting of small, rasp-like, weakly impressed punctures, similar on whole surface of pronotum; interstices with microsculpture. Median carina of prosternum with anterior portion elevated into small tooth in lateral view. Median portion of prosternum 1.2× wider than long, postero-mesal projection with shallow notch, pits laying next to ridges delimiting prosternal plate minute.

MESOTHORAX. Scutellar shield bearing a few small punctures, interstices with fine mesh-like microsculpture. Elytral series 1–6 arising basally, series 7–8 subbasally, series 9 abbreviated anteriorly, undetectable in ca. basal 0.2. Elytral series 7 and 8 markedly closer to each other than to other series. Serial punctures fine and sparse. Elytral intervals weakly convex at suture; intervals 5, 7 and 9 distinctly higher than adjacent intervals; punctation irregular on all intervals, consisting of sparsely arranged, minute punctures. Elytral interstices opaque, with very fine microsculpture. Epipleuron narrowing posteriad, reaching elytral apex. Preepisternal plate suboval, 2.0× longer than wide; median part concave, bearing sparsely arranged coarse setiferous punctures; interstices without microsculpture.

METATHORAX. Punctation of median portion of metaventrite consisting of small, sharply impressed, slightly rasp-like punctures becoming indistinctly smaller laterally, interstices without microsculpture, shiny. Anepisternum 7.2× longer than wide.

LEGS. Tarsi with short and sparse pubescence ventrally.

ABDOMEN. Ventrite 1 without additional longitudinal ridges laterally.

MALE GENITALIA. Parameres 1.2× longer than phallobase, with moderately large inner projection, bearing two short setae apically. Phallobase narrow, 1.8× longer than wide. Median lobe nearly parallel-sided basally, narrowing apicad in apical 0.2; lateral projections large, developed in apical 0.3 of median lobe.

Variation. Anteromedian tooth-like projection of the median carina of the prosternum slightly varies in shape, being lower and less clearly projecting ventrad in some specimens. Fine microsculpture of elytra is only vaguely developed and elytra therefore seem to be more shiny than in holotype in two paratype specimens. In remaining characters, mentioned variable specimens correspond with the holotype. It is probable that the pale coloration of the type specimens is caused by the teneral character of these specimens.

Etymology. Latin latus = broad, the name refers to the wide body shape of this species.

Habitat. Unknown.

Distribution. So far known only from Saint Vincent Island in the Lesser Antilles.

Figures

FIGURES 32 – 35. Habitus of the representatives of O. aequinoctiale group. 32: O. aequinoctiale; 33: O. gibbicolle; 34: O. holosericeum; 35: O. latum.

FIGURES 78 – 83. Prosternal plate in lateral view (78 – 79), elytral intervals (80 – 81) and median portion of metaventrite (82 – 83). 78: O. latum; 79 – 80, 82: O. aequinoctiale; 81, 83: O. holosericeum.