Lilioceris groehni sp. n.: the first authentic species of Criocerinae (Coleoptera, Chrysomelidae) from Baltic amber

Abstract Based on a single well-preserved specimen from Eocene Baltic amber, Lilioceris groehni sp. n. is described and illustrated using phase-contrast X-ray microtomography. It is the first described species of Criocerinae (Coleoptera: Chrysomelidae) from Baltic amber. A check-list of fossil Criocerinae is provided. Placement of Crioceris pristiana (Germar, 1813) is discussed, this species is removed from Criocerinae and placed in Coleoptera incertae sedis.


Introduction
The subfamily Criocerinae (shining leaf beetles) contains ca. 1500 extant species (Schmitt 1996) in 20 genera (Seeno and Wilcox 1982), of which 211 species in 6 genera are recorded from the Palaearctic region (Schmitt 2010). The genus Lilioceris Reitter, 1913 comprises ca. 170 extant species distributed over the temperate, subtropical and tropical regions of the Palaearctis, Orientalis, Aethiopis including Madagascar, and the Australis, and was introduced to North America by man (Monrós 1960, plus records from the Zoological Record up to present as taken from the Index to Organism Names).
Shining leaf beetles are rarely represented in fossil material and especially in Baltic amber (Table 1). Two fossil species from Baltic amber were mistakenly described within Criocerinae. Electrolema baltica Schaufuss, 1892 was described as member of Criocerinae but later transferred to Hispinae (Korschefsky 1939). According to modern classification (Staines 2012), it is placed in Gonophorini Chapuis, 1875 within Cassidinae. Another species, Crioceris pristina (Germar, 1813) originally described as Criocerina (Germar 1813) was mentioned within Criocerinae (e.g. Giebel 1856aGiebel , 1856bSpahr 1981;Santiago-Blay 1994). In our opinion it is not a member of the Criocerinae (see Discussion).

Material and methods
The specimen is included in an amber piece that was polished by hand and facetted on their sides, allowing improved views of the included specimens. The material examined is deposited in the collection of the Geological-Palaeontological Institute of the University of Hamburg, Germany [GPIH], as part of the collection of Carsten Gröhn.
Observations were made using a Nikon SMZ 745T stereomicroscope. Photographs were taken using a Canon EOS 70D with a 100 mm macro lens, and a Canon EOS 5D with the Canon MP E 65 mm macro lens in a visionary digital bk plus lab system by Dun Inc. The microCT-images were produced by means of an Xradia Micro XCT-200 (Carl Zeiss X-ray Microscopy Inc.), using the 4x object lens units, at 30kV and 4W, with a pixel size of 5.36 µm. Tomography projections were reconstructed using the reconstruction software provided by XRadia. Volume rendering of image stacks was performed by using Amira 5.6.0 (FEI Visualization Science Group, Burlington, USA) using the "Volren" or "Voltex" function. The specimen considered here was assigned to the family Chrysomelidae based on the pseudoteramerous tarsi and the lack of a rostrum and of antennae not inserted on pronounced tubercles, to the subfamily Criocerinae because the prothorax does not bear side borders and the frons has distinct diverging grooves behind the antennal insertions, and to the genus Lilioceris based on (1) free tarsal claws and (2) divided vertex separated from the neck by a dorsal constriction.
Differential diagnosis. Head, body, and elytra of Lilioceris groehni sp. n. appear unicolorous black and thus similar to the extant species L. hitam Mohamedsaid, 1990 from Borneo, which differs from the new species in (1) the shape of the pronotum (distinctly longer than wide with its constriction at the middle), (2) metaventrite glabrous in the middle, (3) pubescent scutellum, (4) impunctate elytra (with few moderately large punctures at base only), (5) vertex with sparse pubescence, (6) a distinct conical neck between head and pronotum, and (7) a larger body (10 mm).
Head hypognathous, transverse, widest across eyes, together with eyes nearly as wide as pronotum, strongly constricted behind the eyes forming a neck (Fig. 3); shiny, hairless and without distinct punctures dorsally. Compound eyes large, strongly convex, deeply and acutely notched at antennal insertions; distance between eyes nearly as wide as transverse diameter of one eye. Frontal grooves deep, crossed forming X. Vertex convex, hairless, with median longitudinal groove. Genae large, with sparse pubescence. Antennae poorly visible because of a beetle location in amber piece. Antennae robust, covered with fine pubescence, moderately long, extending nearly to basal one-fourth of elytra, slightly widened apically; antennomere 2 shortest, about 0.4 times as long as antennomere 3, antennomere 4 sligthly longer than antennomere Pronotum nearly as long as wide, deeply constricted medially, distinctly narrower than elytra, widest in anterior one-third; impunctate, shiny; disc flattened, with an arcuate transverse depression subbasally (Figs 3 and 4). Anterior margin straight me- dially; posterior margin convex; lateral margins rounded anteriorly and strongly constricted just behind middle; all margins not bordered. Anterior and posterior angles obtusely rounded. Scutellum large, triangular; apparently hairless and impunctate. Elytra subparallel, widest in the middle, about 1.5 times as long as wide; humeri prominent. Elytral punctures small and dense (in basal one-third deeper), arraged in rows; scutellar row present, short; intervals flat, only at apices weakly convex.
The interior of the abdomen does not contain any identifiable structure, as revealed by the microCT-analysis. No traces of an aedeagus could be found, and none of the smaller particles -all covered with homogeneous material -could be addressed as the spermatheca.
Derivatio nominis. This new species is named after Carsten Gröhn (Glinde, Germany) -he enabled us to study this specimen.

Discussion
The specimen of Lilioceris groehni sp. n. appears externally complete. However, the fact that we found no traces of internal structures in the abdomen, especially of an aedeagus, does most probably mean that (1) the specimen was a female, and (2) that it remained openly accessible for scavengers and/or detritivores before it was covered by resin. This could also provide a possible reason for its black appearance as the dead individual might have been exposed to humic acids before being fossilised. If this should be the case, the live animal had most probably a habitus similar to the extant lily beetles. Actually, L. groehni sp. n. is hardly distinguishable from extant Lilioceris-species. In this respect, the new species is quite normal. Hennig (1966) wrote that it is "a long known fact" ["eine altbekannte Tatsache"] that the morphological differences between fossils from Baltic amber and their extant relatives are only minute".