Arostropsis groehni Yunakov & Kirejtshuk

Yunakov, Nikolai N. & Kirejtshuk, Alexander G., 2011, New genus and species of broad-nosed weevils from Baltic amber and notes on fossils of the subfamily Entiminae (Coleoptera, Curculionidae), ZooKeys 160, pp. 73-96 : 76-81

Arostropsis groehni Yunakov & Kirejtshuk sp. n. Figs 1-16

Material examined.

Holotype "C 7968, GPIH 4516", male (GPIH); the complete beetle with a clear integument is included in an irregular parallelepiped with the largest plane about 18.0 × 14.0 mm and the smallest one 11.0 × 7.0 mm; amber matter on right side from the beetle is rather homogeneous, but that from the left side of the inclusion consists of some layers, in which between the borders is a fine net of dark (almost blackish) organic matter.

Etymology.

The epithet of the new species is formed from the name of Carsten Gröhn, collector of its holotype.

Type strata.

Baltic Amber; Upper Eocene, Prussian Formation.

Type locality.

Baltic Sea coast and Amber quarry Jantarny near Kaliningrad (formerly Koenigsberg), Kaliningrad region, Russia.

Description.

Length 6.4, width 1.8, height 1.3 mm. Body slender, distinctly depressed from above. Pronotum and elytra strongly carinate at sides. Integument densely covered with small, apparently metallic, lanceolate (apparently green) scales at both sides of body and legs.

Head. Rostrum 1.5 times as long as wide, narrow, distinctly narrower than head capsule, laterally depressed. Pterygia weakly extending beyond lateral contour of rostrum. Epistomal area not depressed. Lateral edges of epifrons at middle convex, narrowed towards middle, then parallel-sided, without basal, transverse depression or sulcus. Median sulcus shallow, extending towards pit between eyes, not continuing towards vertex. Head capsule not constricted beyond eyes. Frons distinctly convex, almost twice as wide as epifrons at level of antennal insertions. Maximum width of head at posterior part of eyes. Scape comparatively short, about 1/4 as long as funicle, strongly expanded apically, somewhat compressed dorsoventrally, not extending beyond anterior third of eyes, directed obliquely downwards in folded state. Funicle slender; all segments elongate, funicular segment 1 about three times as long as wide, 2nd about two times as long as wide, 3rd about 1.5 times as long as wide; 4th-5th about two times as long as wide, segments 6 -7 about 1.5 times as long as wide. Club spindle-shaped and comparatively thin, with distinctly separated segments, about as long as funicular segments 1-7 together. Mandibles entirely bare (without scales), moderately extended beyond buccal cavity. The only remaining left mandibular process knife-shaped, in apical third slightly curved inward, without internal prominences, about 1.5 times as long as protruding part of mandibles.

Pronotum elongate, almost parallel-sided, with anterior and posterior constrictions widely expressed, weakly and evenly convex at sides, with disc weakly convex transversely and anterior edge curving upward; posterior edge slightly bisinuate; posterior angles widely rounded and somewhat projecting posteriorly; anterior edge nearly straight.

Elytra elongate, about 4.5 times as long as wide, parallel-sided, humeral prominences distinct (Fig. 8, hp), basal edge of elytra biconvex opposite the posterior pronotal depressions. Elytral declivity gently sloping (Fig. 7).

Legs slender. Femora slender, elongate, obtuse, weakly swollen in apical third. Tibiae slender and elongate. Protibiae gently curved inwards in apical third; with anterior row of thin spines. Metatibiae subflattened and with inner edge sinuate at apical third. Corbels open (Figs 6, cb; 8), without additional row of spines. Tarsi slender, setaceous, pelma well-developed (term after Doyen 1966). Tarsomere 1 almost as long as tarsomeres 2-3 combined. Ultimate tarsomere extended beyond lobes of tarsomere 3 by length of last one. Claws free. Procoxae comparatively small, situated in middle of prothorax (Fig. 8).

Comparison with recent genera.

The new genus differs from all recent genera of Naupactini with open corbels and procoxae not completely separated from the prosternum ( Mesagroicus Schoenherr, 1840, Eurymetopus Schoenherr, 1840, Melanocyphus Jekel, 1875, Trichonaupactus Hustache, 1939) in the following characters: short and depressed scape, rostrum narrow, epistomal area weakly setose, epifrons with a weakly developed median depression and vertex with very small fossa, not continuing to occiput.

Comparison with Baltic amber entimine genera.

Since Arostropsis gen. n. has free claws, only two other fossil genera, Paonaupactus Voss, 1953 and Protonaupactus Zherikhin, 1971, share the same character state and can be compared with the new genus. Arostropsis gen. n. strongly differs from both Paonaupactus and Protonaupactus in the following characters given in the key below.

Key to Baltic amber genera of Entiminae with free claws

Systematic position

This new genus is undoubtedly a member of Entiminae due to the presence of mandibular processes. Due to structural characters: mandibular processes long, knife-shaped (ibt not developed) - claws free, vertex and epifrons combined in uniform structure without transverse sulcus before eyes, the new genus could be assigned to the tribes Naupactini or Geonemini Gistel, 1848. Emden separated these groups from other ‘brachyderoid’ tribes of Entiminae with free claws ( Tanymecini and Anypotactini ) by the following characters (Table 1).

The position of Arostropsis is tested following the table:

Presumption 1 ( Geonemini ). Arostropsis gen.n. lacks the key characters of Geonemini such as: evenly sloping lateral edges of epifrons, very narrow vertex and anterior position of procoxae. Consequently this genus cannot be assigned to this tribe..

Presumption 2 ( Tanymecini ). Arostropsis gen. n. could not be considered in the tribe Tanymecini , due to absence of postocular vibrissae at the prothorax. The amount of vibrissae varies from genus to genus within Tanymecini but at least a few vibrissae are present (some Pandeleteius ). We do not know any case in which vibrissae are completely absent, so it is unlikely that Arostropsis belongs to Tanymecini .

Presumption 3 ( Anypotactini ). Due to absence of transverse sulcus between vertex and epifrons and U-shaped epistome in Arostropsis it is impossible to consider this genus within Anypotactini .

Presumption 4 ( Naupactini ). The strictly lateral position of the eyes, flattened epifrons and very broad vertex resembles that of Arostropsis within Naupactini , however, the shape of the rostrum is very different from that of any known member of this tribe. This transformation of rostrum probably resulted in reduction of the frontal fossa (Fig. 10) that is normally (in genera with broad rostrum) deep, long and continuing from the anterior portion of epifrons to the occiput. Such head shape together with the unusual slender body makes it difficult to recognize Arostropsis as a member of the tribe Naupactini .

Probable bionomy. The long legs and well developed tarsal pelma (term after Doyen 1966) of the new species suggests that this beetle was capable of running swiftly between leaves and, therefore, it was likely a canopy-dweller.