Thyreocephalus unicolor Sharp, 1885

Márquez, Juan & Asiain, Julieta, 2016, Taxonomy of the Mexican species of Thyreocephalus Guérin-Méneville (Coleoptera: Staphylinidae, Xantholinini), Zootaxa 4169 (2), pp. 251-285 : 256-258

Thyreocephalus unicolor Sharp, 1885

(Figs. 1a, b, 5a, 6g, 8a–c, 9a, 11a, 12a)

Thyreocephalus unicolor Sharp, 1885: 500

Total body length 17.0– 21.5 mm. Body glossy black, except maxillary and labial palps, and genital segment that are reddish; antennomeres 4–11 gray.

Head round shaped, with convex lateral margins, not forming posterior corners; proportion length/width of head 0.93 in males and 1.04 in females; width of head respect to width of pronotum 1.59 times in males and 1.37 in females; dorsal and ventral surfaces almost flat in lateral view. Dorsal surface with sparse umbilicate punctures heterogeneously distributed, dense at median level of eyes backward and laterally, sparse at anterior half; some punctures arranged in two (sometimes three) short rows at center of head (Fig. 1a). Ventral surface with very dense umbilicate punctures on sides, sometimes combined with roughness, becoming less dense toward the center (Fig. 1b). Eye 0.23 times as long as head. First antennomere twice the length of second and third antennomeres combined, third 1.7 times the length of second, fourth and fifth almost quadrate, 6–10 transverse. Labrum with two pairs of apical teeth, the external pair smaller and acute, the central pair wider and acute on their external corners ( Fig. 5 a). Mandibles 0.67 times as long as head. Neck with a small sunken, arcuate shaped area, with one or two pairs of deep points laterally (Fig. 1a).

Pronotum with anterior corners slightly wider than posterior corners, with punctation as in remaining species (Fig. 1a). Scutellum with 6–8 fine punctures and microsculpture as wavy lines. Elytra 1.12 times as long as pronotum, with sparse punctures heterogeneously distributed, except by an impunctate belt parallel to the lateral border.

Prosternal sclerite faintly divided by a fine longitudinal line. Prosternum with posteromedian carina moderately developed, intercoxal carina acute ( Fig. 6 g). Mesocoxae broadly separated by mesosternum; metasternum with sparse long setae.

Abdomen glossy, with microsculpture as wavy lines; first four visible tergites with an area slightly sunken parallel to anterior border; postero-lateral areas of first three visible sternites with wider and superficial punctures than punctures on remaining areas. Aedeagus median size (length = 1.66 mm), elongate-oval, slightly wider at base; apex of median lobe conic shaped, apical area of median lobe 0.2 times the total length; parameres symmetrical, homogeneously wide (except their acute apex) and long (0.37 times the length of median lobe); internal sac poorly visible, occupying almost all the length of median lobe, slender, microsculpture partially visible ( Figs. 9 a, 11a).

Variation. In addition to the variation of the total body length, the proportion length/width of the head can be sexually dimorphic, because in males (n= 4) the average value was 0.93 (head longer than wide) and in females (n= 4) of 1.04 (almost as long as wide). Another variation possibly related to the sex is the width of head with respect to the width of pronotum, resulting in males having a head wider than pronotum (average 1.59 times, n= 4) in comparison with the same proportion in females (average 1.37 times, n= 4). Finally, the aedeagus shows variation in total length from 1.6 to 1.7 mm (n= 4).

Diagnosis. Thyreocephalus unicolor can be confused with T. jalapaensis and T. sp. aff. subtilis due to their similar pattern color. It is distinguished from T. jalapaensis because this last species has a shorter body length, narrower head, with parallel sides, labrum with three pairs of apical teeth, dense and conspicuous punctation on the elytra, and a distintive size and form of the aedeagus; whereas T. unicolor is bigger, with wider head, with convex sides, two pairs of apical teeth on the labrum, elytra with less dense punctation, and a different size and form of the aedeagus. Thyreocephalus unicolor can be distinguished easily from T. sp. aff. subtilis by the black elytra, without blue metallic reflection, and with lower density of punctation, a long body, head rounded, a sunken area on the neck and by the aedeagus. In T. sp. aff. subtilis the elytra have blue metallic reflection, dense punctation ( Fig. 7 ), body shorter than T. unicolor , head less rounded, different size and form of the sunken area on the neck, and different aedeagus.

Discussion. Even if this species can be distinguished without difficulty from other Mexican species, Sharp (1885) pointed out that it is similar to T. salvini Sharp, 1885 , although also he indicated that it can be easily distinguished by the different color of the elytra (metallic blue in T. salvini ), pattern of punctation on the head, and the posteromedian carina on the prosternum of T. unicolor ( Figs. 6 g, 8a–c). Also, Sharp (1885) observed one specimen with a wider head than remaining two specimens he examined and he considered this as probably sexual variation, as we observed in this work ( Fig. 8 a–c). This discussion and the following in several species point out the need to study the remaining Neotropical species.

Natural history. This species has been collected inside bromeliad flowers, below leaves and below fallen bromeliads in cloud forests ( Sharp 1885).

Distribution ( Fig. 12 a). This species is known only from the southeast of Mexico (part of the Sierra Madre Oriental), particularly in the states of Hidalgo, Puebla and Veracruz ( Table 2 ) ( Sharp 1885, Navarrete-Heredia et al. 2002).

Material examined. " Mexico: Hidalgo, 3 km N de Tlanchinol, N 21° 1.328´, W 98° 38.77´, 1430 m, bosque mesófilo de montaña, en hojarasca, 1-IV-2003, J. Asiain y J. Márquez cols." (1♂ 1♀, CC-UAEH); " Mexico: Hidalgo, Tepehuacán de Guerrero, Chilijapa, N 21° 12´5.1", W 98° 51´8.21", 1401 m, bosque mesófilo de montaña, en tronco podrido, 19-IV-2013 , J. Márquez col." (1♂, CC-UAEH); " Mexico: Puebla, km 3 carretera Xicotepec—Barranca de Patla , 1130 m, 12-VII-1994 , A. Casasola col." (1♂, CNIN); " Mexico: Puebla, km 40 carretera Tulacingo—Xicotepec de Juárez , 13-VII-1994, E. Barrera y C. Mayorga cols." (1♀, CNIN) ; " Mexico: Veracruz, Xalapa , Rancho Guadalupe, km 2.5 Antigua Carretera a Coatepec, bosque mesófilo de montañacafetal, 1360 m, en luz, VIII-2000, col. R. Novelo. " (1♂, IEXA) ; " Mexico: Veracruz, Xico , camino a Oxtlapa, N19° 25´46", W 97° 01´42", parche de bosque, ex bromelia caída, 21-VI-2000, 1390 m, E. Montes de Oca y Q. Santiago cols." (1♀, MUZ-UV); same data as previous, except: " N19° 25´10", W 97° 02´09", 1330 m " (♂ 1, MUZ- UV).

Additionally we analyzed a photograph of one syntype of T. unicolor from Jalapa, Veracruz, Mexico provided by R. Booth from The Natural History Museum.

Figures

FIGURE 5. Dorsal view of the labrum of: a) Thyreocephalus unicolor, b) T. sp. aff. subtilis, c) T. jalapaensis, d) T. scutellaris, e) T. puncticeps, g) T. rufipennis, h) T. halffteri, i) T. arizonicus.

FIGURE 6. Ventral view of the pronotum showing the posteromedian carina (lacking in b) and the postcoxal process in: a) Thyreocephalus puncticeps, b) T. sp. aff. subtilis. Lateral view of the pronotum showing the develop and variation of the posteromedian carina in: c) T. puncticeps, d) T. arizonicus, e) T. scutellaris, f) T. jalapaensis, g) T. unicolor.

FIGURE 7. Photographs of: Thyreocephalus subtilis, a) syntype mounted on a plate with label data (provided by BMNH), b) close-up of the same syntype specimen (BMNH). Thyreocephalus sp. aff. subtilis, c) male specimen studied (Xalapa, Veracruz), d) female specimen studied (Xalapa, Veracruz), e) specimen of T. subtilis from Peru (not studied, only photo; AMNH). Scale = 5 mm.

FIGURE 8. Photographs of Thyreocephalus unicolor: a) syntype mounted on a plate with label data (not studied, only photo provided by BMNH), b) male specimen studied (Xico, Veracruz), c) female specimen studied (Xico, Veracruz). Thyreocephalus arizonicus: d) dorsal view of the examined paratype (male, CNC), e) ventral view of the aedeagus of the paratype, with internal sac everted, f) ventral view of the aedeagus of an examined specimen from Morelos, Mexico. Scale = 5 mm (a – d), 1 mm (e – f).

FIGURE 9. Ventral view of the aedeagus of: a) Thyreocephalus unicolor, b) T. sp. aff. subtilis, c) T. jalapaensis, d) T. scutellaris, e) T. cribripennis, f) T. rufipennis, g) T. halffteri. Scale = 0.5 mm.

FIGURE 12. Geographic distribution and individual track of: a) T. puncticeps (black squares) and T. unicolor (black circles); b) T. arizonicus (gray squares), T. jalapaensis (black circles) and T. rufipennis (white circles).

Tables

TABLE 2. Mexican species of Thyreocephalus with country and state records (Herman 2001, Navarrete-Heredia et al. 2002, Asenjo 2004, Newton et al. 2005, Asenjo et al. 2013). * First Mexican record, ** first Mexican state record.

Species	Previous records	First Mexican (*) and state records (**)
T. unicolor	Mexico: Veracruz	**Hidalgo and **Puebla
T. sp. aff. subtilis ( T. subtilis )	None (Antilles, Brazil, Colombia, Panama, Peru and Venezuela)	Possibly: *Mexico: Veracruz (The identification need verification, see discussion in taxonomic information)
T. jalapaensis	Mexico: Hidalgo and Veracruz. USA: Texas
T. scutellaris	Mexico: Chihuahua	**Hidalgo, **Jalisco, **Morelos and **Zacatecas
T. cribripennis	Mexico: Veracruz
T. puncticeps	Mexico: Colima, Estado de México, Guerrero, Jalisco, Michoacán, Morelos, Nayarit, Oaxaca and Sonora	**Zacatecas
T. rufipennis	Guatemala: San Geronimo. Mexico: Oaxaca
T. halffteri	Mexico: Jalisco and Nayarit	**Estado de México, **Guerrero, **Michoacán, **Morelos and **Zacatecas
T. arizonicus	USA: Arizona	*Mexico: Estado de México, Jalisco and Morelos