Georissus (Neogeorissus) nemo, Fikáček & Delgado & Gentili, 2012

Fikáček, Martin, Delgado, Juan A. & Gentili, Elio, 2012, The Hydrophiloid beetles of Socotra Island (Coleoptera: Georissidae, Hydrophilidae), Acta Entomologica Musei Nationalis Pragae 52, pp. 107-130 : 112-116

Georissus (Neogeorissus) nemo sp. nov.

( Figs. 8 , 9–14 , 17–18 )

Type locality. Yemen, Socotra Island, Hallah Arhar, 12°33.0′N 54°27.6′E, 15 m a.s.l.

Type material. HOLOTYPE: J ( NMPC): ‘ YEMEN: Socotra Isl. / Hallah Arhar (spring) / 12°33.0′N 54°27.6′E, 15 m / 11.xi.2010, leg. J. Hájek’ . PARATYPES: 1 ♀, 6 spec. ( NMPC, KSEM, NHMW, IRSNB): same label data as the holotype ; 62 spec. ( BMNH; NMPC, KSEM, 10 spec. in DNA grade in coll. NMPC): ‘ YEMEN: Socotra island / Halla area , Arher ; freshwater / spring in sand dune / 9.-10.+ 15.vi.2012 / 12°33.0′N 54°27.6′E, 5 m // Socotra Expedition 2012 / J. Bezděk, J. Hájek, V. Hula / P. Kment, I. Malenovský, / J. Niedobová & L. Purchart’ ; 1 spec. ( NMPC): ‘ YEMEN: Socotra Island / ca. 3 km NE of Shuab / Avicennia marina mangrove ; / sand dunes, 20.-21.vi.2012 / 12°34.1′N 53°23.9′E, 3 m // SOCOTRA expedition 2012 / J. Bezděk, J. Hájek, V. Hula / P. Kment, I. Malenovský, / J. Niedobová & L. Purchart leg. ’.

Description. Body weakly elongate, lowly convex in lateral view. Body length 1.3–1.5 mm (holotype 1.4 mm), width of head 0.35–0.45 mm (holotype 0.37 mm), maximum width of pronotum 0.5–0.6 mm (holotype 0.5 mm), maximum width of elytra 0.75–0.95 mm (holotype 0.80 mm). Coloration elytra and pronotum reddish brown to brown with olive reflections, head dark brown.

Head ( Fig. 10 ). Clypeus weakly convex, with scattered sparsely arranged granules, anterior margin with marginal row of densely arranged granules; each posterolateral portion of clypeus anteriorly to eye declined, divided from mesal portion by ridge arising from frons, ridge high and sharp posteriorly, but more weakly defined anteriorly before joining with marginal clypeal row of granules. Frons with central elongate depression surrounded by elevated ridges each bearing several weakly pronounced granules; anterior portion of frons with sharp sublateral ridge without granules at midlength between central depression and inner margin of each eye (this ridges continues to clypeus more anteriorly); submesal portion with transverse blunt ridge connecting midlength of central ridge with posterior portion of sublateral ridge. Eyes large, oval in lateral view.

Prothorax ( Figs. 11–12 ). Pronotum 1.1× as wide as long, with maximum width at posterior 0.4; lateral portions very small, slightly projecting laterad as blunt elongate lobes only. Anterior portion with two closely situated submedian ridges delimiting shallow median groove, each side laterally of ridges weakly convex, with scattered granules. Central portion of pronotum with large but rather shallow rhomboid depression delimited by wide granuliferous ridges anteriorly and narrow ones posteriorly, posterior ridges not joining but converging to posterior margin; posterolaterally of central depression with pair of large but shallow impressions delimited laterally by small granuliferous bulge; posterolateral portion of pronotum each with high granuliferous protuberance. Posterolateral pits absent. Ventral morphology of prothorax corresponding with G. crenulatus .

Mesothorax. Elytra ( Figs. 9, 13 ) combined 1.2× as long as wide, 2.2× as long as pronotum; base of elytra ca. as wide as maximum width of pronotum, maximum width of elytra between anterior 0.1–0.5, elytra gradually narrowing in posterior 0.5–0.2, apex strongly narrowed. Elytral suture and intervals 2, 4 and 6 elevated into high narrow ridges, ridge on interval 6 arising from large humeral protuberance; lateral portion with Y-shaped structure formed by highly elevate interval 8 and anterior portion of interval 9; odd intervals (1, 3, 5) flat, not elevate, interval 7 flat anteriorly and becoming slightly elevate posteriorly. All ridges and humeral protuberance with very weak and low granules only, hence the elytral ridges nearly smooth; odd elytral intervals only with scattered and extremely low granules, hence appearing nearly totally flat. Elytral series regular, serial punctures small but sharply impressed. Lateral-most portion of elytron declined, hence elytral laterally without clear projections. Median pentagonal protuberance of mesoventrite flat, without distinct pits.

Metathorax. Metaventrite ca. 2× as long as mesoventrite, flat, only with few scattered indistinct granules, without distinct median discrimen. Metathoracic wings present in specimens examined for this character (n=2).

Abdomen ( Fig. 14 ) gradually narrowing posteriad. Ventrites 1 flat, only with sparsely arranged indistinct granules especially in posterior third (anterior portion of some specimens totally bare), ventrites 2–4 without granules, ventrite 5 flat with few indistinct granules along posterior margin.

Male genitalia ( Fig. 8 ). Aedeagus 0.4 mm long (measured in holotype only). Parameres 0.85× as long as phallobase, their combined width slightly narrower than maximum width of phallobase; lateral margins of parameres very slightly convergent in basal 0.6, arcuately bent inward apically; apex widely obtusely pointed; inner margins straight, well sclerotized. Median lobe 0.75× length of parameres, narrowly triangular apically, apex sharp, gonopore situated subapical, struts ca. 0.4× as long as apical portion of median lobe. Phallobase slightly widening posteriad, with wide but indistinct latero-posterior band along margins, without posterior opening.

Differential diagnosis. Based on the general sculpture of the pronotum (i.e., rhomboid central depression and low submedian and higher lateral tubercles, Fig. 11 , 17 ) and elytra (i.e., odd intervals more elevated than even ones), Georissus nemo sp. nov. belongs to the G. costatus species group sensu DELÈVE (1967a,b). It may be distinguished from other species of the group by the combination of the following characters: elytral ridges highly elevated, very weakly denticulate in lateral view; intervals 2, 4 and 6 nearly completely flat with very few indistinct granules; lateral portions of pronotum not projecting into acute lobes; abdomen with very indistinct granules on ventrites 1 and 5 only; phallobase slightly longer than parameres, only indistinctly widened posteriad; parameres widely arcuate apically. By elytral morphology, G. nemo sp. nov. especially resembles the African species G. alticosta Grouvelle, 1909 and G. decorsei Paulian & Legros, 1943 , and G. decoratus Delève, 1972 from Sri Lanka, all of which may be easily distinguished by the morphology of the aedeagus which is much narrower in both African species ( DELÈVE 1967a, Fig. 8 ) and much wider in G. decoratus ( DELÈVE 1972, Fig. 16 ). Georisus nemo sp. nov. also differs from both African species by the indistinctly denticulate elytral costae (costae are totally smooth in G. alticosta and G. decorsei ) and from G. decoratus by flat elytral intervals 2 and 4 (slightly convex in the latter species).

Georissus nemo sp. nov. may be easily distinguished from the following unidentified species from Socotra Island by its smaller body size (the other species is 1.8–2.0 mm long), elytral costae with very indistinct denticulation (strongly denticulate in the other species), elytral intervals 2 and 4 flat (convex and bearing many distinct granules in the other species), abdominal ventrites with extremely indistinct granulation (with very distict granulation on whole ventrites 1 and 5 in the other species), and by the weakly metallic coloration (head and pronotum strongly and elytra moderately metallic in the other species). From the third Socotran species of Georissus , G. maritimus sp. nov., it differs by its costate odd elytral intervals.

Etymology. The species name refers to Captain Nemo, a fictional character of two novels by Jules Verne, who lived underseas (in a submarine Nautilus), hence in an environment unusual for a human. This resembles specimens of Georissus nemo sp. nov. collected in 2010 which were found underwater, in an environment unusual for this genus.

Collection circumstances. The vast majority of specimens in the type series were collected in Arhar along the permanent stream rising below the sand dunes on the base of rock cliffs of the Socotra Plateau falling to the sea coast. The specimens inhabited the sandy waterlogged surroundings of the stream partly overgrown by short-grazed lawn of few undetermined Poaceae and Cyperaceae and surrounded by shrubs of Tamarix nilotica (Ehrenb.) Bunge (Tamaricaceae) . The majority of the specimens were collected at night, creeping on the bare wet sand, while a portion of the specimens were attracted at light trap installed close to the stream. In 2010, when the locality was only shortly visited in the daytime, few specimens were found on the submerged underside of the stones directly in the stream. One specimen was also found among a large number of G. maritimus sp. nov. from the type locality of the latter species (see above).

Distribution. Known from two distant localities on Socotra Island, indicating that the species may be widely distributed on suitable habitats of the island.

Notes. Although the relationships between the species of Georissus Latreille, 1809 are poorly known and the species groups defined by the pronotal and elytral sculpture may be easily polyphyletic, the strong resemblance of G. nemo sp. nov. to some African and Sri Lankan species (see Differential diagnosis) is rather striking. Moreover, there is a long series of an undescribed Georissus species in NMPC which was collected in southern India (Tamil Nadu state, S of Tuticorin) in salt marshes at the Támbrapathi river estuary, hence in a habitat somewhat resembling that of G. nemo sp. nov. The Indian species is very similar to G. nemo sp. nov. by dorsal sculpture, male genitalia and highly reduced abdominal granulation, although it shows some weak differences from G. nemo sp. nov. (elytral intervals 2 and 4 slightly convex, body coloration strongly metallic) and therefore seems to represent a separate species. Even though further studies of the Indian specimens are needed to completely understand their identity, the strong resemblance between both taxa suggests that G. nemo may possibly represent a South Indian element of Socotran fauna.

Figures

Figs. 7–8. Genitalia of Socotran endemic Georissus species. 7 – G. maritimus sp. nov. (a, b: two different ventral views of the same aedeagus; c: lateral view); 8 – G. nemo sp. nov., ventral view.

Figs. 9–14. Georissus nemo sp. nov. (9–13 – paratype; 14 – holotype). 9 – pronotum and elytra in dorsal view; 10 – head, dorsal view; 11–12 – detail of pronotum (11 – dorsal view; 12 – dorsolateral view); 13 – elytron, dorsolateral view; 14 – abdomen.

Figs. 15–22.Socotran endemic Georissus species and their habitats. 15–16 – G. maritimus sp. nov.(15 – dorsal view; 16 – lateral view). 17–18 – G. nemo sp. nov. (17 – dorsal view; 18 – lateral view). 19–20 – the sand tongue 3 km NE of Shuab, type locality of G. maritimus sp. nov. (19 – general view of the habitat; 20 – satellite view showing the position of the locality); 21–22 – the stream at Arhar, type locality of G. nemo sp. nov. (21 – general view of the habitat; 22 – satellite view showing the position of the locality).