Three new minute leaf litter beetles discovered by citizen scientists in Maliau Basin, Malaysian Borneo (Coleoptera: Leiodidae, Chrysomelidae)

Abstract Background We coin the term "taxon expeditions" for citizen scientists' field courses to carry out publishable taxonomic work in close association with trained taxonomists. New information During the first-ever taxon expedition, in Maliau Basin Studies Centre, Sabah, Malaysian Borneo, the participants sampled leaf litter beetles from lowland dipterocarp forest using the Winkler apparatus. The collected material proved to contain at least three undescribed species of small-bodied (ca. 1 mm long) hemispherical litter-dwelling Coleoptera. As part of the field course work, taxonomic descriptions were prepared for the chrysomelid Clavicornaltica sabahensis sp. n. and the leiodids Colenisia chungi sp. n. and Dermatohomoeus maliauensis sp. n.


Introduction
During tropical biology field courses, it is common for students to practise field ecological methods using quantified sampling of various groups of invertebrates. Except for rare exceptions (e.g. Miller et al. 2014), after sorting and (coarse) identification, the specimens are usually discarded or stored as bulk samples, even though the materials are likely to be of taxonomic importance. We have recently begun a series of field courses for citizen scientists (which we term "taxon expeditions"; see http://www.taxonexpeditions.com) in which a taxonomic treatment of selected taxa forms a central part of the course work. We believe that this serves two important purposes: (i) a better appreciation for the practice of taxonomy amongst the general public and (ii) valid taxonomic output.
The Taxon Expeditions concept involves ten days of lectures and workshops in a wellequipped field research centre, during which the citizen scientists are trained in basic field and lab. techniques for biodiversity assessment and identification. Under the guidance of embedded taxonomists, the participants identify and describe new taxa belonging to the taxonomists' field of expertise. The collected materials are stored in a local collection and provided with voucher numbers that are referred to in all output such as published taxonomic treatments, web-based taxonomy platforms, and 3rd-generation DNA sequencing of DNA barcodes in the field (Menegon et al. 2017).
In this paper, we provide the first output from this model, viz. taxonomic treatments for three new species of minute Coleoptera that were collected from leaf litter in tropical lowland forests in Borneo using Winkler extraction. The taxa belong to (a) the leaf beetle genus Clavicornaltica Scherer, 1974 (a relatively recently discovered genus that is likely to be highly diverse in tropical leaf litter biotas; Scherer (1974), Konstantinov and Duckett (2005)) and (b) the leiodid genera Dermatohomoeus Hlisnikovský, 1963 andColenisia Fauvel, 1903, two speciose genera that are widespread thoughout Africa, Asia, Australia, and the Pacific islands, but which have not yet been studied extensively in Borneo. An accompanying paper on Elmidae (Coleoptera) will appear elsewhere.

Materials and methods
We sampled at 4. 7389°N, 116.9696°E, at 260 m elevation, at a location where a small stream enters the Maliau River along the Seraya Trail of the Maliau Basin Studies Centre (Sabah, Malaysian Borneo). Six course participants and two course instructors collected leaf litter from the space between the plank roots of large trees ("buttress sample") and from the open forest floor in between ("floor sample"). The two samples were similar in amount (ca. 15 l). The litter was first sieved using a 1-cm-mesh beetle sieve (Fig. 1) and the flow-through was then placed inside Winkler bags, which accumulated the emerging invertebrates in pure ethanol over a period of four days. Then, the Coleoptera were picked from the samples and from these, the Leiodinae (Leiodidae) and Galerucinae (Chrysomelidae) were selected for further treatment.
In the buttress sample, 1 specimen of Clavicornaltica (Galerucinae), 2 specimens of Colenisia Fauvel and 2 specimens of Dermatohomoeus Hlisnikovský (Leiodinae: Pseudoliodini) were found. The floor sample yielded no materials from these genera. Citizen scientists on the first Taxon Expedition in Malaysian Borneo performing leaf litter sieving. During this exercise, three new species of minute leaf litter beetles were discovered.
Three new minute leaf litter beetles discovered by citizen scientists in ... The specimens were studied and their morphological features documented using the limited equipment available at the field centre, i.e. a Nikon SMZ445 with 20x eye pieces (magnification up to 70x), a Canon EOS 500D with MP-E 65 mm lens placed on a Kaiser copy stand with micro-drive, and basic dissection materials. Lengths of body parts were measured by photographing a ruler with 0.5 mm line spacing alongside the specimen and then measuring both the ruler and the body parts from the photographs. Ratios of antennomeres and body parts were also calculated from measurements taken from photographs. Spacing of punctures and other microsculptural elements was, where possible, measured from electron micrographs. Drawings were done freehand and proportions may therefore deviate somewhat from reality. The material was compared with all relevant taxonomic literature (see below). Dissected genitalia, antennae, and other body parts were embedded in PVP embedding medium (Lompe 1986) and mounted either on a mounting board or on a glass micro-slide and attached to the same pin as the specimen. All specimens were given collection numbers of the Borneensis (BORN) collection of the Institute for Tropical Biology and Conservation at Universiti Malaysia Sabah and stored there permanently.
In addition, specimens were studied of the same genera collected by Winkler extraction at another site in Maliau Basin (Ginseng Camp, 670 m elevation; Chung et al. 2010) and held in the collection of the Forest Research Centre at Sepilok, Sabah (FRCS). These specimens were used for scanning electron micrographs using a JEOL JSM-7600F. The FRCS does not use collection numbers. Colenisia Fauvel, 1903; Type species: Colenisia caledonica Fauvel, 1903 Nomenclature Colenisia Fauvel, 1903;(Fauvel 1903, Newton 1998, Daffner 1991, Švec 2013

Description
Length of body 1.25 mm. Maximum width of elytra 0.86 mm. Head width (including the eyes) 0.46 mm. Greatest width of pronotum 0.8 mm. Winged. Short and oval, shiny and sparsely pubescent, dark chestnut, angles of pronotum, strip along suture, and head dark ochre (Fig. 2). Legs and antennomeres I-VI yellow, antennomeres VII-XI orange. Entire dorsum transversely microsculptured.
Head: Ratio of horizontal width of eye (measured in dorsal view and perpendicular to the longitudinal axis of the head) to distance between eyes: 1:7.4. Transverse microsculpture recognisable but too fine to distinguish individual cells at 50x a b Figure 2.
a: Female, dorsal view (paratype, BOR/COL/14091) b: Female, lateral view (paratype, BOR/COL/14091) magnification (distance between individual striae is 3-5 µm; Fig. 3a). At 50x magnification, no punctuation is clearly visible. Length of antennomere III 0.8 times the length of antennomere II. Antennomere XI slightly wider than antennomere X ( Elytra: Broadest at basal quarter, roundly curved to apex. Surface with transverse microsculpture. Microsculpture much more pronounced than on the pronotum, already recognisable at 15x magnification. Individual horizontal striae separated from one another by ca. 20 µm (about the width of antennomere III). Punctures separated by around 5-8 times their own diameter, irregularly arranged, each with a hair that can be up to 30 µm long (Fig. 3c). Sutural stria absent.
Legs: Anterior tarsomeres I-IV not markedly widened in the male.
Aedeagus: Median lobe elongated, parallel-sided, at the tip extended into a flat processus reminiscent of a duck-bill. Parameres thin, short, two-thirds of the length of the median lobe, slightly widened at the tip and provided with two long hairs, each about one-third of the length of the paramere itself (Fig. 4a). In lateral view, the median lobe is gently curved and apically flattened into a wedge (Fig. 4b).
Spermatheca: A near-spherical bulb with a tube about twice as long as the diameter of the bulb and about a third of its diameter. Tube from its base narrowing to about half its own diameter towards the terminus.

Diagnosis
The eye size, dorsal microsculpture, shape of aedeagus and antenna, as well as the presence of irregularly arranged punctuation on the elytra, place this species near C. championi (Portevin 1937) from South India, C. pecki Daffner 1988 from Japan and C. castanea Švec 2011 from China. However, C. championi has longer parameres and a less clearly sinuous outline of the aedeagus apex (Daffner 1991). C. pecki has the 11th antennomere much smaller than in C. chungi. C. castanea has acute posterior angles of the pronotum and a more stocky aedeagus (Švec 2011).

Etymology
Named in honour of Dr. Arthur Y. C. Chung, who collected the first known specimen in 2005.

Distribution
Known only from two locations in the valley where the Maliau river flows out of Maliau Basin, located at 290 m elevation (Maliau Basin Studies Centre) and 670 m elevation (Ginseng Camp).

Ecology
Only collected from leaf litter on the forest floor in lowland dipterocarp tropical rainforest. The two specimens from the Maliau Basin Studies Centre were both collected from between buttress roots, whereas leaf litter from the forest floor yielded no specimens. Perhaps this is an indication of its preferred microhabitat.

Description
Length of body c. 1.4 mm (Fig. 6). Oval, 1.45x longer than wide, greatest width at the shoulders. Pronotum 2.0x wider than the head. Winged. Reddish brown, with yellow legs and antennae. Eyes large. Antennae slender, antennomere VII 1.5x as long as wide. Pronotal posterior angle not drawn out, only a very faint convex curve next to the rounded angles. Elytra sparsely pubescent, with distinct punctuation, here and there arranged into longitudinal rows. All punctures on the elytra connected by microreticulation.
Head: Eyes large, each with an estimated 40-50 ommatidia. Ratio of horizontal width of eye (measured in dorsal view and perpendicular to the longitudinal axis of the head) to distance between eyes: 1:4.4. A thin supraorbicular groove runs along the inner margin of the eyes and over the antennal insertion. Length of antennomere III 0.7 times the length of antennomere II. Antennomere IX slightly narrower than antennomere X. Antennomeres X and XI of equal width (Fig. 9). Punctuation (when viewed at 50x magnification) distinct, individual punctures spaced by 3-5 times their diameter (Fig.  7a). No microreticulation visible.
Pronotum: Broadest at the base. Pronotal posterior angle rounded, not drawn out, the pronotal basis near the posterior angle with only a very faint convex curve. Pronotum smooth, glossy, hairless, without any microreticulation but with very fine and sparse punctuation, punctures spaced at 3-5 times their diameter, nearly invisible at 50x magnification (Fig. 7b). A fine, continuous margin runs along the lateral and anterior margin.
Aedeagus: Median lobe in dorsal view gradually narrowing towards the apex, terminally shaped into a broad, mushroom-shaped plate that is twice as wide as long (Fig. 8a). scanning electron microscopy). In lateral view (Fig. 8b), the median lobe is basally strongly curved ventrad, but in the terminal one-third curved gently dorsad and flattened into the shape of a thin wedge. Dermatohomoeus maliauensis sp. n., male, antenna (drawn after electron micrograph) (paratype, FRCS)

Diagnosis
As pointed out by Švec (2009), Dermatohomoeus species are often very similar externally and the male genitalia offer the only certain identification. The shape of the aedeagus separates D. maliauensis sp. n. from nearly all Dermatohomoeus species for which the male genitalia are known. One species with similar male genitalia is the widespread D. portevini (Champion, 1923). The size of the body and eyes, the microsculpture of the dorsum, and the shape of the pronotum indeed place the new species in the close vicinity of D. portevini. However, in D. portevini the median lobe of the aedeagus displays a bulge directly basal of the terminal plate (Daffner 1988), which is not the case in D. maliauensis sp. n. Also, the 7th antennomere is broader in D. maliauensis. A second species with a similar aedeagus is D. bidentatus Švec & Cooter 2015 from Yunnan, China which, however, is characterised by the two lateral teeth at the terminus of the median lobe; moreover, it is nearly twice as large (Švec and Cooter 2016). Another species that appears to possess similar external characteristics is D. terrenus (Hisamatsu 1985) from Korea and Japan. This species is thought to be parthenogenetic, as no males are known (Park and Ahn 2007). D. terrenus differs from D. maliauensis sp. n. in having an 11th antennomere that is distinctly broader than the 10th and by transverse microsculpture on the pronotum, which is absent in D. maliauensis sp. n.

Etymology
Named after Maliau Basin Conservation Area in Sabah, Malaysian Borneo. This 30km-wide circular depression, covered with montane forest on poor soils and surrounded by steep sandstone cliffs, is known as "Sabah's Lost World". It is the focal area for the Borneo work of Taxon Expeditions. The species epithet was selected during a naming ceremony in Maliau Basin Studies Centre on 6 October 2017, in which expedition participants as well as a large number of field centre staff and porters took part. As far as the authors are aware, this is the third animal species named for this under-explored area (Disney 2016, Buhl 2009).

Distribution
Known only from two locations in the valley where the Maliau river flows out of Maliau Basin, located at 260 m elevation (Maliau Basin Studies Centre) and 670 m elevation (Ginseng Camp).

Clavicornaltica Scherer, 1974
Nomenclature Clavicornaltica Scherer, 1974;(Medvedev 1996, Scherer 1974, Konstantinov and Duckett 2005 Diagnosis Small (0.7-2.2 mm), convex flea beetles, with strongly developed jumping hind legs and characteristically clavate antennae. Frons is broad, antennal insertions widely separated. Antennae 11-segmented, clavate after the 3rd antennomere. The first three antennomeres are long and slender, the next three very small, the final five are enlarged and form a club. Pronotum with two setal pores, the anterior of which is placed behind the middle of the lateral margin. Metasternum with an anterior-pointing, broad processus. Posterior femora strongly dilated. Metatibia slender and with a long terminal spore and a row of smaller terminal setae on the lateral edge.

Description
Body dark reddish brown, small, oval and convex, ca. 0.75 mm long and ca. 0.58 mm wide (Fig. 10a). Eyes ca. 1/7 the width of the head. Antennae yellowish brown; clava long and moderately robust. Female wingless. Tibia and tarsus yellowish brown, femur dark brown and robust. Male unknown.
Pronotum: Lenticular in dorsal view, convex, four angles angular with a deep furrow along the length of the edge, which itself is somewhat angular in the middle with two deep seta-bearing pores: one at ¼ of the margin's length, the other in the posterior angle. Punctuation covers the entire surface in an irregular pattern and is the same strength as the dorsal surface of the elytra.
Elytra: Striae punctiform, punctures shallower dorsally, more deeply impressed laterally and becoming less visible towards the very apex. A deep but narrow punctuated groove runs along the entire margin continuing to the apex; apex itself slightly drawn out.
Legs: Metafemur robust, oval, covered in fine white setae. Metatibia bearing eight minute setae which cover the terminal one-quarter along the external edge and one long spine, slightly shorter than the first tarsomere, provided with three minute teeth (Fig. 12).

Etymology
Since this is the first species of Clavicornaltica found in Sabah, the specific epithet sabahensis ("inhabitant of Sabah") was chosen. This was one of several names suggested during a naming ceremony in Maliau Basin Studies Centre on 6 October 2017, in which expedition participants as well as a large number of field centre staff and porters took part.

Distribution
Known only from one location in the valley where the Maliau river flows out of Maliau Basin, at 260 m elevation (Maliau Basin Studies Centre).

Taxon discussion
Only a single female was at the authors' disposal. Nonetheless, the authors felt confident that this specimen represents an undescribed species. First of all, given their small size, apterism/brachypterism, and habitat (leaf litter in forests), it is unlikely that Clavicornaltica species have wide ranges (Konstantinov and Duckett 2005) and the only species known from Borneo and its immediate vicinity have external characters that do not match C. sabahensis sp. n. (see under Diagnosis). Moreover, C. sabahensis sp. n. carries a combination of traits that make it easily recognisable. Specifically, these are its extremely small size, highly vaulted shape, dark colouration, narrow ridge on the first abdominal sternite, angular, thick pronotal margin, and strong punctuation on the entire elytra.

Discussion
While we believe that taxonomic work is best carried out in the context of large, genusencompassing revisions by experts, we think that rapid taxon treatments of single species based on limited materials, such as we present here, have value. As digital techniques are becoming available that allow the aggregation of information from various sources, even small studies such as this one contribute to the knowledge of taxa. Provided that care is taken to (a) diagnose each species such that it can be recognised when found again and (b) avoid the introduction of junior synonyms, we think that even citizen scientists, if guided by properly trained taxonomists, can help close the large gap in the knowledge of the biodiversity of the world's invertebrates.
Moreover, the present results are the outcome of the first field trip of what is aimed to become a twice-yearly series of taxon expeditions to Maliau Basin. As our future work and publications will also focus on small leaf litter Coleoptera, we expect that knowledge of these and related, co-existing species will rapidly expand.

Author contributions
I.N. conceived and initiated this study. As part of the field course exercises, under the guidance of M.S., L.S. studied and drew Clavicornaltica sabahensis. S.O. wrote the descriptions of Colenisia chungi and Clavicornaltica sabahensis. M.S. wrote the description of Dermatohomoeus maliauensis. M.S. and I.N. drafted the final manuscript. J.S. provided logistical support and was instrumental in organising the event during which names for the new species were selected.