Arra legalovi, 2014

Peris, David, Davis, Steven R., Engel, Michael S. & Delclòs, Xavier, 2014, An evolutionary history embedded in amber: reflection of the Mesozoic shift in weevil-dominated (Coleoptera: Curculionoidea) faunas, Zoological Journal of the Linnean Society 171 (3), pp. 534-553 : 537-541

ARRA LEGALOVI PERIS, DAVIS ET DELCLÒS SP. NOV.

( FIGS 1–3 )

Coleoptera Nemonychidae , in Soriano et al. (2010: fig. 3).

Etymology

The specific epithet legalovi is in honour of Andrei Legalov, for his contribution to the knowledge of the fossil weevils.

Holotype

CPT –4106 ( Figs 1 , 2 ), housed at the Conjunto Paleontologico de Teruel-Dinópolis (Teruel, Spain). The holotype is a well-preserved specimen inside a relatively transparent piece of amber with some impurities, imaged by synchrotron microtomography. The holotype was initially conserved as a syninclusion with a chironomid fly ( CPT –4107).

Paratype

CES –576 ( Fig. 3 ), from the El Soplao amber outcrop, housed at the Institutional Collection located in the laboratory of the El Soplao Cave . The holotype is a well-preserved specimen, but the piece of amber in which it is contained has several impurities and there are limitations to viewing the individual .

Type locality

CPT –4106 is from the San Just site, in the municipality of Utrillas, near the village of Escucha ( Teruel , Spain). The piece was found in the Escucha Formation (upper part of the Regachuelo Member), early Albian in age ( Peñalver et al., 2007) . CES –576 is from the El Soplao site, in the municipality of Celis (Cantabria, Spain). The piece was found in the Las Peñosas Formation, early Albian in age ( Najarro et al., 2009) .

Diagnosis

As for the genus (vide supra).

Description

Body length 1.82 mm (including rostrum), maximum body width 0.47 mm, ratio of body length to greatest width 3.87; body dorsoventrally flattened with very few rounded margins, elliptical in section in metathorax and abdomen; dorsal surface with appressed pubescence dense and sparse.

Head slightly narrower than pronotum, long, straight behind compound eyes, not constricted; compound eyes large, slightly elongate, rather coarsely faceted, convex and moderately protruding; compound eyes not separated by more than one compound eye diameter ( Fig. 1A ). Rostrum 3.7 times as long as wide in apex, 6.0 times as long as wide in middle and at base, 1.4 times as long as prothorax, as narrow as forehead and nearly linear, apex widened ( Fig. 1A ). Mandibles protruding at oblique angle with rostrum. Antennae subapical, dorsally inserted close to mandibular articulations; antennae not reaching pronotum when directed posteriorly. Antennae with 11 articles, last three forming a very loose club. Scape large, forming longest article, 1.3 times length of pedicel, somewhat rounded apically and laterally straight; pedicel (funicular article 1) to funicular article 7 similar in shape, narrower at base and wider apically, pedicel 1.6 times as long as funicular article 2, slightly increasing in size from funicular articles 2 to 6; article 7 slightly narrower than 6 ( Fig. 3A ); club articles 1 and 2 (antennomeres 9 and 10, respectively) 1.3 times wider than funicular article 6, both similar in shape; club article 3 (antennomere 11) similar in width to club article 2 but 1.6 times longer and acute apically ( Figs 1B–C , 3A ).

Prothorax length 0.31 mm, width 0.27 mm; prothorax 1.1 times as long as wide; pronotum semiquadrate, anterior angles close to orthogonal; pronotal lateral margins subacute, distinctly carinate, nearly parallel; base of prothorax narrower than elytra. Precoxal part elongate, 3.0 times as long as diameter of procoxal cavities. Procoxal cavities situated near posterior margin of prosternum, separated by about one procoxal diameter; procoxae hemispherical and weakly protruding ( Fig. 1B–D ). Mesocoxal cavities somewhat widely separated, distance more than width of antennomere, longitudinally orientated. Metacoxal cavities horizontally orientated, widely separated but less than width of one metacoxa; metacoxae extending laterally, but not reaching elytra, completely separated from metaventrite by transverse suture of metaventrite.

Mesoscutellum wider anteriorly and acute posteriorly, subtriangular and with rounded angles ( Fig. 3A ). Elytral length 0.91 mm, width 0.41 mm. Elytra elongate, 2.0 times as long as combined width at middle and 1.4 times as wide as pronotum at humeri; weakly convex, slightly wider at middle, gently arcuate apically and basally, almost parallel-sided, widely rounded at apex, with humeri subrectangular and only slightly rounded; about 1.3 times wider at middle than at humeri, distinctly punctate-striate and with sutural striole; rounded apically; epipleura distinct ( Figs 1 , 3 ).

Abdomen with five visible ventrites ( Fig. 1D ). Abdominal process on anteromedial margin of ventrite 1 wide and rounded apically. Abdominal ventrite 1 longest, 1.8 times as long as ventrite 2, with anterior part excavated behind metacoxae; ventrites 1 to 5 decreasing in width and length, with a reduction in length of 0.9 times previous segment. All tergites covered by elytra.

All legs similar in length ( Fig. 1 ); trochanters long, femora attached to trochanters obliquely; femora compressed, wider medially; femora excavated on inner part for reception of tibiae; tibiae similar in length to femora, wider apically; tibial spurs 2–2–2. Tarsal formula 5–5– 5; tarsal length shorter than tibiae; pro- and mesotarsi with tarsomeres narrow, linear, tarsomeres 1 to 4 decreasing in length and slightly lobed ventrally, tarsomere 5 longest, almost 0.3 times total tarsal length; metatarsi with five tarsomeres, but tarsomeres 4 and 5 partially fused, seemingly forming a single tarsomere ( Fig. 1B, C ), only separated by faint suture ( Fig. 2B ), tarsomeres 2 and 3 slightly bilobed ventrally ( Fig. 2B ); pretarsal claws appendiculate, nearly appearing bifid.

Remarks

Kuschel (1995) provided a list of synapomorphies for Rhinorhynchinae ( Nemonychidae herein) in adults; larval characters are discussed in May (1993): (1) right mandible with prostheca, (2) punctation on elytra aligned to striae, (3) mesonotum with stridulatory file, (4) tarsomere 2 truncate-emarginate, (5) pretarsal claws appendiculate, (6) aedeagus with apodemal bridge, without flagellum. Of these characters, it was possible to view only characters 2 and 5 in the fossil, thereby assigning the species to Rhinorhynchinae . There are 54 species and 19 genera in this subfamily. Tribal placement of these specimens is somewhat less clear, although the visible suite of characters appears to allow its placement in Mecomacerini . A list of synapomorphies for Mecomacerini was provided in Kuschel & Leschen (2010): (1) terminal segment of maxillary palps about as long as scape, (2) prosternum in front of procoxae as long as or shorter than procoxae, (3) procoxae weakly protruding and hemispherical, (4) mesocoxae about as far apart as antennal club width. Owing to the preservation of the fossil, it is difficult to differentiate the maxillary palpi. The labrum is visible in the synchrotron images, and appears to bear several pairs of setae, although this observation is not definite. Although the procoxae are positioned near the posterior end of the prosternum in this new genus (thereby contrasting with one of the above-hypothesized synapomorphies for the tribe), this character is also observed in some other genera within Mecomacerini (e.g. Aragomacer Kuschel, 1994 ). The mesocoxae are separated slightly more than the antennal club width, although not by much. In agreement with the above list, the procoxae are weakly protruding, the shape being somewhat elongate and hemispherical. Another apparent feature shared by the majority of Mecomacerini is the enlarged, elongate, convex, coarsely faceted compound eyes, which are separated on the forehead by approximately the width of the rostral apex. Although such deviations in the synapomorphies of the extant genera within Mecomacerini exist in this new genus, it is quite possible that this taxon represents an early-diverging branch of this lineage (i.e. a potential stem group). Considering the metatarsi, which display partially fused tarsomeres 4 and 5 ( Fig. 2B ), a condition appearing autapomorphic because extant Mecomacerini clearly have a 5–5–5 tarsal formula, Arra legalovi gen. et sp. nov. could be considered representative of some extinct, Cretaceous lineage amongst rhinorhynchine Nemonychidae . Nevertheless, we consider the set of characters insufficient for erection of a new tribe.

Libanorhinus Kuschel et Poinar, 1993 , was described from Early Cretaceous (Aptian) amber of Lebanon and was placed in the extinct subfamily Eobelinae ( Kuschel & Poinar, 1993) . Libanorhinus is certainly a unique member of the family conserved in Mesozoic amber, but unfortunately the specimen is severely damaged, thereby preventing any revision. The simple pretarsal claws, the contiguous procoxae, and the bilobed third tarsomeres are sufficient characters to differentiate Libanorhinus from Arra gen. nov., which has appendiculate pretarsal claws, separated procoxae, and tarsi that are only slightly lobed ventrally (including the third tarsomeres).

The fossil genus Cratomacer Zherikhin et Gratshev, 2004 , was described in Rhinorhynchini (Rhinorhynchinae) from the Early Cretaceous (Aptian) of Santana in north-eastern Brazil ( Zherikhin & Gratshev, 2004) and later transferred to Mecomacerini (Rhinorhynchinae) by Kuschel & Leschen (2010). It clearly differs from Arra gen. nov. in the antennae being inserted along the middle of the rostrum, a transverse head, and contiguous procoxae, contrasting with Arra gen. nov., which possesses antennae inserted close to the mandibles, a long head, and separated procoxae. Although Cratomacer immersus Zherikhin et Gratshev, 2004 , appears to possess non-bilobed third tarsomeres, this feature is rather uncertain in Cratomacer ephippiger Zherikhin & Gratshev, 2004 (it actually appears more bilobed than not in the holotype). A plethora of additional nemonychid fossils of various forms from the Jurassic of Karatau ( Kazakhstan) was described by Arnoldi (1977), Gratshev & Zherikhin (1995, 1996), and Legalov (2010a, 2010b). Although an impressive diversity is documented from this deposit, it seems that forms with simple, linear tarsomeres (non-bilobed) have yet to be uncovered.

Figures

Figure 1. 3D reconstruction of Arra legalovi gen. et sp. nov. (CPT–4106, holotype), from Early Cretaceous San Just amber (Spain), using propagation phase-contrast X-ray synchrotron microtomography at beamline ID19, ESRF, Grenoble. A, dorsal habitus; B, right lateral habitus; C, left lateral habitus; D, ventral habitus; E, anterior habitus; F, posterior habitus.

Figure 2. Photo and detail of Arra legalovi gen. et sp. nov. (CPT–4106, holotype), from Early Cretaceous San Just amber (Spain). A, dorsal habitus; B, camera lucida drawing and photo of the metatarsus, showing the partially fused tarsomeres 4 and 5, suture marked with an arrow.

Figure 3. Photos and drawing of Arra legalovi gen. et sp. nov. (CES–576, paratype), from Early Cretaceous El Soplao amber (Spain). A, camera lucida drawing and photo of the dorsal habitus, arrows mark the seventh funicular article, slightly smaller than the preceding ones; B, ventral habitus; C, lateral habitus.