An unusual new genus of spider beetle (Coleoptera: Ptinidae) from a guano island of Peru

A new genus and species of spider beetle from Peru is described. One specimen is known to have come from South Chincha Island, while others were intercepted in a guano shipment in Texas, USA. Unusual characters of this genus include a small cavity laterally on each side of the metepisternum and very broad spacing between the antennae. The potential biology and evolutionary relationships of this genus are briefly discussed


INTRODUCTION
The coast and offshore islands of Peru are lined with numerous guano deposits, a resource that has been exploited for use as a fertilizer for centuries by the Inca and in more recent history (Hunt, 1973;Cushman, 2005). The guano boom from 1840-1870 has long disappeared, but a small global demand by organic farmers continues to this day (Romero, 2008). One international guano shipment was intercepted at Corpus Christi, Texas in 1972 containing the species here described, but the original locality of these specimens is unknown. However, an additional specimen collected from one of the Chincha Islands in 1935 was later discovered in unsorted museum material.
Several island-dwelling spider beetle (Coleoptera: Ptinidae) genera exist, with some taxa sharing similarities in morphology. For example, Pitnus Gorham is globally widespread, with described island species in the Antilles and the Galapagos, as well as coastal Central America, western Mexico, southern Australia, and one inland species reported from Arizona, United States (Bellés, 1992). Neoptinus Gahan is found on both Christmas Island and mainland Australia. Three genera, Casapus Wollaston, Piarus Wollaston, and Stereocaulophilus Bellés, are endemic to the Canary Islands. We take this opportunity to describe another possible island endemic that was discovered on South Chincha Island, located about 20 km offshore from Pisco, Peru.
Diagnosis Diagnosis. This genus is distinguished from all other known spider beetle taxa by the combination of the head visible from above (Fig. 1A), relatively short, ninesegmented antennae ( Fig. 2A)   flat interantennal space (Figs 1D,2A). Most notable is the presence of a shallow ovoid cavity located on the anterio-lateral part of each side of the metepisternum (Figs 1C, 3D, 6B). This depression is partially covered by the elytron and there is a darker ring around the perimeter formed by thicker cuticle internally. This taxon is perhaps most similar to Pitnus, but members of this latter genus have a body with a length of ~1 mm and are black in color in contrast to this genus with a body ~2.5 mm in length that is reddish brown in color.
Legs short in length; procoxae conical and strongly projecting, mesocoxae ovoid and projecting; metacoxae completely fused with metathorax with no trace of suture, slightly excavate at trochanter insertion; trochanters small, ovoid, increasing in size from pro-to metatrochanter; femora gradually expanding to apical 1 / 3 , slightly tapering to apex; tibiae slender, increasing in girth slightly from base to apex; all tarsi 5 segmented, fifth distinctly longer than the others, tarsomeres 2-4 on pro-and mesolegs as wide as long (Figs. 1B, C, 3B, C).
Etymology: The generic name comes from the Latinized Greek roots "xeno-", meaning strange, and "cotylus", meaning cup, referring to the unusual cavity on each side of the metathorax. The gender is masculine. Diagnosis. This species can be distinguished from any congeners by its reddish brown coloration with light yellow setae, the rugose texture of the elytra, and arrangement of punctation. The presence (and perhaps the form) of the cavities on the metepisternum may be distinctive to this species if additional taxa belonging to this genus are discovered. Currently the only known precise locality is South Chincha Island, Peru.
Elytra surface rugose, fine suberect setose punctures in somewhat irregular rows along and between remnant puncture rows, punctures sometimes appearing slightly darker than surrounding surface, setae angled towards posterior, in some locations punctures arranged in close pairs spaced roughly the width of one puncture apart (Fig. 6A).
Ventral Surface finely reticulate, except for meso-and metasternum; covered with apically pointing setae, more dense generally than those on elytra.
Etymology: The specific name is from the Latin root "latus" , meaning wide, and frons. This refers to the particularly wide interantennal space.
Distribution: Currently the only record for this species is South Chincha Island of the coast of Peru south of Lima (Fig. 4). A guano shipment from Peru to Corpus Christi, Texas, where several beetles were intercepted, gives no precise information on origin. Hence it remains to be discovered if this genus is present on other islands along the Peruvian coast (Fig. 5) and possibly on the mainland.

DISCUSSION
An unusual ovoid cavity is present laterally on each metepisternum (Figs. 1C, 3D, 6B). The small opening to this chamber is visible below the lateral margin of the elytron and is obscured by a dense brush of minute setae. This visible opening is connected to a larger cavity hidden under the elytra and extending to the dorso-lateral edge of the metepisternum. The role of these cavities is unknown but may function in a similar manner as trichomes. Trichomes, hair-like structures which collect glandular excretions to appease predatory ants, are known in three New World spider beetle genera, Gnostus Westwood, Fabrasia Martinez & Viana (Lawrence & Reichardt, 1966), and Coleoaethes Philips (Philips, 1998). However, ants are reported as being very scarce on Peruvian guano islands (Murphy, 1925). It is possible that the species or lineage evolved on the mainland in the presence of ants before a founder event to the single island from where this species is known.
Nothing is known of the feeding habits of this genus. The only known locality, South Chincha Island, provides one obvious potential food source: seabird guano. Although guano is acidic and possibly an unfavorable food source, Bellesus Özdikmen has been observed feeding on lizard droppings in Venezuela (Philips, unpublished), feces which are similar to those produced by birds. This taxon might also feed on accumulated plant detritus. The morphologically similar Pitnus is notable for its habit of feeding on coastal vegetation as either a leaf miner  or a seed head feeder (Philips & Keller, unpublished). But as plants are mostly absent on Peruvian guano islands, this association seems less likely. Resolving the ecology of this genus may require observation of beetles in situ.
This genus bears close similarities to members of the sphaericine group of spider beetles (see Philips & Mynhardt, 2020). With Pitnus and Neoptinus, it shares the trait of 9-segmented antennae, an uncommon number in spider beetles which typically have 11 antennomeres. These genera also show a relatively broad interantennal space, though not as developed as in Xenocotylus. The structure of the abdominal ventrites in Xenocotylus and Neoptinus is very similar, displaying a high degree of fusion between segments 1-3 and an abrupt narrowing point between these and segments 4 and 5. Due to the wide geographic separation between the two, it is possible that any characteristics shared by Xenocotylus and Neoptinus but perhaps not Pitnus developed independently. The wide distribution of Pitnus, including species nearby in both the Galapagos Islands and coastal Peru (Whorrall & Philips, unpublished), supports Pitnus as the most likely sister group to Xenocotylus.
Of further note is the association of some of these characters with the traditional anobiid beetles. Wide interantennal spacing is a key character differentiating the anobiids from the spider beetles (i.e., Ptinidae sensu stricto). The female genitalia in this genus also bear a resemblance to the typical form in anobiids. Other characters, however, validate placement among the spider beetles, especially the connate first three abdominal ventrites, reduced length of the fourth (Figs. 1B, 3C), and rounded pronotal lateral margins (Figs. 1C,  3A). Nevertheless, this new genus challenges a distinct division of the two groups. Acquisition of DNA quality specimens should be a major goal for use in future family level phylogenetics of Ptinidae.

ACKNOWLEDGMENTS
Our thanks to Warren Steiner who passed onto TKP a vial of these beetles that were intercepted in the USA. Also, our sincere appreciation to the two anonymous reviewers that made some useful suggestions that improved the manuscript.