Redescription of Xenicopoda Moore and Legner (Coleoptera: Staphylinidae, Omaliinae), with Supplementary Notes.
Psyche 84(2):142-149, 1977.
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REDESCRIPTION OF XENICOPODA MOORE AND LEGNER (COLEOPTERA: STAPHYLINIDAE, OMALIINAE),
WITH SUPPLEMENTARY NOTES*
Museum of Comparative Zoology, Harvard University, Cambridge, Mass. 02138
Moore and J-egner (1971) described a new genus and species of Omaliinae, Xenicopoda helenae, on the basis of a unique specimen of undetermined sex collected on Mt. Wilson, California. The ma- jor distinguishing character they noted for this genus (op. cit. and Moore and Legner, 1974) was the bizarrely modified protarsi, quite unlike any previously described in the Omaliinae. Since then I discovered a series of six X. helenae in the H. C. Fall Collection at the Museum of Comparative Zoology. Exam- ination of these specimens showed that the unusual front tarsi found on the type are present only in males. Females have normal female omaliine protarsi, slender and with equal tarsal claws. This distinct difference between the sexes and the availabil- ity of additional specimens of Xenicopoda made it seem worth- while to publish an amplified description of the genus. Detailed study of the type and the six other specimens also led to the dis- covery of a number of discrepancies between the specimens and the original description. The proportions as given in the description and as shown in the original habitus drawing are rather distorted, owing partly, perhaps, to the fact that the type is somewhat curled up. Proportions based on careful measurements of the seven avail- able specimens will be mentioned below. The head shape in the original drawing is rather distorted as well, and a new figure is given.
*Manuscript received by the editor November 3, 1977 142
Thyer - Redescription of Xenicopoda
Length: mean 2.5 mm (2.0-2.7 mm), measured as is (slightly curled); estimated actual length 3.0 mm (2.5-3.6 mm). Head about seven-tenths as long as wide (from clypeal apex to nuchal constriction), epistomal sulcus absent (fig. 3). Vertex with well-impressed dorsal tentorial pits and small, rather obscure pale ocelli. (The dorsal tentorial pits are presumably what Moore and Legner (1971) meant by anterior tentorial pits. The latter are ac- tually very slight depressions antero-medial to the antennal inser- tions, indicated by short lines there in figure 3.) Weak nuchal constriction across dorsal surface just behind ocelli. Faint micro- sculpture on dorsal and ventral surfaces of head. Labrum nearly rectangular with rounded anterior corners, about 2.2 times as wide as long; margins entire. Mandibles as illustrated (figs. 1, 2) with well-developed molar areas composed of many small, sharp, buc- cally directed teeth. Maxillary palp four-segmented, more or less filiform, with first segment small; second and third segments larger, subequal to each other, more or less obconical; fourth segment at least twice as long as wide (2.1-3.3x, mean 2.5x), tapering toward apex, the whole segment twice as long as the third, but narrower than its apex. Labial palp three-segmented, each segment slightly longer and narrower than the preceding; third segment two to three times as long as wide. Gular sutures distinctly separate, closest at a level just before the hind margins of the eyes and diverging an- terior and posterior to this. Antenna filiform, basal segments dis- tinctly longer than wide, more distal ones becoming successively shorter and broader up to tenth segment, which is very slightly wider than long. First five or six antennal segments glabrous ex- cept for sparsely scattered long setae; segments six or seven to eleven with shorter setae in addition. The shorter setae become progressively denser on the more distal segments, while the longer setae diminish in number and become increasingly restricted to the apical area of each segment.
Pronotum about seven-tenths as long as wide, about half as long as elytra; fairly evenly convex except for a small median basal de- pression; lateral margins evenly arcuate, slightly explanate in basal half; reticulate microsculpture on dorsal surface. In ventral view, postcoxal process of pronotum extends about halfway from lateral
19771 Thayer - Redescription of Xenicopoda 145 pronotal margin to midline of prothorax. Procoxa and protro- chantin very strongly and sharply carinate externally. Prosternum with short acute process barely extending between procoxae ex- ternally. Mesosternum not longitudinally carinate, having a fairly even surface with no distinct depressions fitting against procoxae; with a short rounded process between mesocoxae. Mesocoxae slightly separated, but meso- and metasternum not touching exter- nally. Metasternum without external process between mesocoxae, with a short pair of processes between metacoxae. Metacoxa tri- angular in ventral view, with posterior surface slightly excavate. Apex of coxa slightly explanate laterally, overlapping part of the trochanterofemoral joint when the leg is in a retracted position. All tibiae with vague row of spines along part or all of outer face. Tibiae and tarsi slender except male prolegs as described below. Metatarsus about three-fourths as long as metatibia, first four seg- ments subequal in length, fifth about twice as long as each of first four. Pair of empodial setae between claws on all tarsi, generally about half as long as claws.
Elytra together about 1 .I times as long as wide; without micro- sculpture between punctures; probably extending to about the apex of tergite 4 in life. Elytral epipleuron delimited by a distinct lateral keel. Wings fully developed, with a typical omaliine folding pat- tern (my unpublished data).
Abdomen with fine reticulate microsculpture on dorsal and ven- tral surfaces; intersegmental membranes with brick-wall pattern (with occasional irregularities) typical of Omaliinae (see Hammond, 1971); sternites of segments 2 and 3 apparently without a keel be- tween metacoxae; tergites 2 and 3 somewhat sclerotized, 4 and fol- lowing more so; tergites 4 and 5 each with a pair of small patches of medially-directed microtrichia ("pruinose" or "tomentose" spots of authors; see fig. 4); only segments 3 and 7 bearing paratergites ("margined segments"), segment 2 with sternites extending onto dorsal surface, other segments with narrow membranous joint di- Figs. 1-8.
Xenicopoda helenae Moore and Legner. 1-2. Mandibles; 1 ., ventral; 2., dorsal view. 3. Head, dorsal view (large circles = ocelli, small circles = dorsal tentorial pits). 4. Abdomen, segments 2-8 and (male) genital segment, dorsal view. 5. Eighth abdominal sternite and external female genitalia, ventral view. 6-8. Male genitalia; 6., Genital segment, ventral view; 7.. Aedeagus (as positioned within ab- domen), dorsal view; 8., Genital segment, dorsal view. Membranous areas of geni- talia stippled. Scale line = 0.5 mm.
146 Psyche [June
rectly between tergite and sternite; sternite 8 with median basal process as illustrated in figure 5.
Male: Protibia abruptly broadened just beyond base, its maxi- mum width about twice that of a mesotibia; apical half of outer face with an irregular row of spines intermixed with a few setae; rounded notch at apex on outside of tibia. Protarsus with first four tarsomeres expanded: the first a pedunculate triangle, next three roughly triangular with their anterior apical corners succes- sively more prolonged; ventral surfaces of first four segments with large strap-like setae (except medially); fifth tarsomere distinctly curved ventrally, apex twice as wide as base. Anterior protarsal claw much longer and thicker than all other tarsal claws, about four-fifths as long as protarsus. Posterior protarsal claw normal. Empodial setae on protarsus shorter than usual, about one-fourth as long as posterior claw. Peg setae (see Hammond, 1972) appear to be absent from legs. Genital segment and aedeagus as in figures 6-8. Aedeagus with parameres dorsal within abdomen, internal sac with dense armature.
Female: Protibia slender, similar to meso- and metatibia, spinose along entire outer face. Protarsus narrow (as meso- and metatar- sus), fifth tarsomere only slightly wider at apex than at base; nor- mal slender setae on ventral surface of tarsomeres 1-4. All tarsal claws similar in size and shape. Genitalia as in figure 5, sclerotized spermatheca apparently absent.
Material examined: CALIFORNIA: Los Angeles Co.: Mt. Wilson, 6-111-46, G. P. Mackenzie (Holotype, male) [California Academy of Sciences]; Pasadena, Echo Mt., 18-111-16, 3500 ft., (1 male, 1 female) [Museum of Comparative Zoology]; (Los Angeles Co.?) Pomona Mts., 11-22 (2 males, 1 female) [MCZ]. Santa Barbara Co.: Santa Barbara, 8-11-91 (1 male) [MCZ]. DISCUSSION
The distinctive protarsi of Xenicopoda males may be modified to facilitate grasping females during copulation. There seem to be no corresponding special structures in females, but both the pro- notum and the elytra have fairly sharp lateral margins. Assuming that a male mounts a female dorsally (I have collected Eusphalerum mating this way), he might use his protarsi to grasp her pronotum or elytra in either of two ways: 1) with his tarsi dorsal and tarsal claws ventral to the lateral edge of the body; 2) with the anterior
19771 Thayer - Redescription of Xenicopoda 147 side of the tarsus (including anterior protarsal claws) dorsal and posterior side ventral to the lateral edge of the body. The bifurcate nature of the second to fourth protarsal segments of the male and the lack of setae along the midline of the tarsus lend some credence to the latter hypothesis, but of course only direct observation of mating can confirm or deny any of this speculation. Why only one genus, out of all known Omaliinae, has these tarsi remains a mys- tery. The large strap-like setae on male Xenicopoda protarsi also may be an aid to grasping females in copulation. The presence of modified protarsal setae in at least the males is characteristic of nearly all omaliine genera I have seen (approximately 40, of which at most 5 lack these setae entirely). The form of the modified setae varies: some, like those of Xenicopoda, are strap-like, while others are spatulate, more or less like those of Xanthonomus Bernhauer, as illustrated by Steel (1955). Those of other genera form a con- tinuum between these two types. Rarely, females also have modi- fied setae on the protarsi, and in Eusphalerum, Amphichroum, and PelecomaZium, modified setae are found on all tarsi of both sexes, although in all these cases the setae of the males seem to be broader than those of the females. Males of several genera have modified setae on their mesotarsi as well as on their protarsi. Most Omatiinae have a pair of paratergites on the second through seventh abdominal segments. In their description of Xenicopoda, Moore and Legner (1971) stated that paratergites are present on the fourth and fifth "visible abdominal segments" (=sixth and sev- enth segments), although their figure seems to show paratergites on the seventh and eighth segments. Examination of a cleared Xeni- copoda specimen reveals that only the third and seventh segments bear paratergites. The second segment appears at first to have paratergites, but closer examination reveals that the sternite ex- tends continuously onto the dorsal surface, whereas there is a mem- branous articulation between paratergites 3 and 7 and their respec- tive sternites. Xanthonomus appears to have a simiiarabdomen, but has paratergites present only on the seventh segment (Steel, 1955, description and Figs. 1-2; also I have examined specimens of an apparently undescribed Xanthonomus sp. in the Bemhauer Col- lection). I do not intend to imply, however, that these two genera are related because of their similarity in abdominal structure. To include females of Xenicopoda in Moore and Legner's (1 974) key to North American omaliine genera, couplet 29 should be
replaced by the following:
Abdomen lacking paratergites except on segments 3 and 7; male with large unequal protarsal claws, anterior one much longer and thicker than posterior, sometimes ............................
nearly as long as tarsus
..................... Xenicopoda Moore & Legner -Abdomen with paratergites on segments 3 through 7; protarsal claws equal in both sexes, same size as those .........................
on meso- and metatarsi .30
There are no ecological data on any of the specimens seen. Exam- ination of one cleared specimen, however, revealed the gut to be packed with pollen grains, as in Eusphalerurn spp., Arnphichroum spp., Pelecornaliurn spp., and some Elonium spp. which are found on flowers. The presence of a mandibular mola composed of small sharp teeth is fairly restricted within the Omaliinae, but all of the above-named genera except Eloniurn share this character with Xeni- copoda. (Brathinus spp. and Olophrurn spp., which are not flori- colous, also have molar surfaces composed of separate teeth, but the teeth differ in size, shape, and orientation from those of Arnphi- chroum, Eusphalerurn, Pelecornaliurn, and Xenicopoda.) Pollen- feeding in Eloniurn may well be a secondary development, as most species of this genus seem not to be found on flowers; this possi- bility makes the lack of a toothed mola in the flower-dwelling Eloniurn species less surprising. The other genera mentioned are apparently entirely floricolous as adults. This evidence and the collection dates on the seven known specimens of Xenicopoda sug- gest that an intensive search in February and March on flowers in the fairly restricted area where the genus has been collected might turn up additional specimens of this interesting beetle. The genus Xenicopoda was placed in the tribe Anthophagini by its authors. For the time being it may remain there, pending badly- needed further study of the higher classification of the Omaliinae. I would like to thank D. H. Kavanaugh, California Academy of Sciences, for the prompt loan of the type of Xenicopoda helenae; H. S. Dybas and E. H, Smith, Field Museum of Natural History, for the opportunity to study the type of Xanthonornus toxopeanus
19771 Thayer - Redescription of Xenicopoda 149 (Bernhauer) and to borrow specimens of Xanthonomus sp.; Nancy Hinnebusch for typing the manuscript; and especially my husband, A. F. Newton, Jr., for continual encouragement and advice in the preparation of this paper.
HAMMOND, P. M.
1971. The systematic postition of Brathinus LeConte and Camioleum Lewis (Co1eoptera:Staphylinidae). J. Ent. (B) 40(1): 63-70. 1972.
The micro-structure, distribution and possible function of peg-like setae in male Coleoptera. Ent. Scand. 3: 40-54. MOORE, 1. AND E. F. 1-EGNER.
197 1. A new genus and species of rove beetle from California (Coleoptera: Staphylinidae). Coleopt. Bull. 25: 5 1-53. 1974. Bibliography (1758 to 1972) to the Staphylinidae of America north of Mexico (Coleoptera). and Keys to the genera of the Staphylinidae of America north of Mexico exclusive of the Aleocharinae (Coleoptera: Staphylinidae). Hilgardia 42(16): 5 1 1-563. STEEL, W. 0.
1955. Notes on the Omaliinae (Col., Staphylinidae) (7) The genus Xanrho- nomus Bernhauer. Entomol. Mon. Mag. 91: 275-278.
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