Thyreocephalus

Márquez, Juan & Asiain, Julieta, 2016, Taxonomy of the Mexican species of Thyreocephalus Guérin-Méneville (Coleoptera: Staphylinidae, Xantholinini), Zootaxa 4169 (2), pp. 251-285 : 255

Key for the identification of adults of the Mexican species of Thyreocephalus

1. Body completely black or black with elytra having a fine metallic blue tint......................................... 2

1´. Body black or dark brown, with elytra reddish to yellow....................................................... 4

2(1). Head big, rounded, wider than long in males (proportion length/width = 0.93) and almost as long as wide in females (proportion = 1.04) (Fig. 1a). Labrum with two pairs of teeth, external acute and internal less developed, near plane ( Fig. 5 a). Neck with a sunken area more or less rounded and small, and several small pits on sides (Fig. 1a). Elytra with superficial, sparse punctures. Length of aedeagus l.6– 1.7 mm, apical area of median lobe 0.20 times the total length, parameres slightly wider, except at apex ( Figs. 9 a, 11a)............................................................... T. unicolor Sharp

2´. Head smaller and less rounded, slightly longer than wide in males and females (1.07–1.10 times) (Figs. 1c, 2a). Labrum with two or three pairs of teeth larger than in T. unicolor ( Figs. 5 b, c). Neck with sunken area formed by two cavities that are interconnected by a fine anterior suture (Figs. 1c, 2a). Elytra with dense and deep punctation. Aedeagus small (length 1.0– 1.4 mm), apical area of median lobe 0.26–0.28 times the total length, slim parameres ( Figs. 9 b, c)............................. 3

3(2). Dorsal surface of head with fine punctures denser than umbilicate punctures (Fig. 1c). Ventral surface of head with corners and sides with dense umbilicate punctures, sometimes forming rugose areas (Fig. 1d). Labrum with two pairs of acute teeth, the internal pair slightly larger ( Fig. 5 b). Prosternum without posteromedian carina, only with intercoxal carina ( Fig. 6 b). Elytra having a fine metallic blue tint, slightly longer than pronotum (1.1 times). Aedeagus 1.4 mm in length, apical area of median lobe narrow at anterior third ( Fig. 9 b)......................................... Thyreocephalus sp. aff. subtilis Sharp

3´. Dorsal surface of head with sparse umbilicate punctures on anterior half (at eye level) and denser toward posterior half, at center of head some punctures form two closed rows ( Fig. 2 a). Ventral surface of head with sparse umbilicate punctures, almost homogeneously distributed, without rugose areas ( Fig. 2 b). Labrum with three pairs of teeth ( Fig. 5 c). Prosternum with posteromedian carina poorly developed in addition to intercoxal carina ( Fig. 6 f). Elytra dark brown to black, without metallic tint, as long as pronotum. Aedeagus 1.0– 1.1 mm in length, apical area of median lobe conical (narrowed from the base) ( Fig. 9 c)....................................................................................... T. jalapaensis Bordoni

4(1). Total body length less than 14 mm. Apical half or apical third of fifth visible abdominal segment, all sixth and genital segments reddish to yellow. Neck with a sunken area of median size with pyramidal shape ( Fig. 2 c). Prosternum with posteromedian carina poorly developed ( Fig. 6 e). Aedeagus small (length 0.85–0.95 mm), with large parameres, 0.4 times length of median lobe ( Figs. 9 d, 11d)................................................. T. scutellaris (Sharp) (? = T. dugesi (Casey))

4´. Total body length more than 14 mm. Abdomen homogeneously black or dark brown, only genital segment can be slightly paler, but not clearly reddish. Neck with one or two sunken areas moderately long and with form not pyramidal. Prosternum with posteromedian carina more developed. Aedeagus longer than 1 mm, parameres less than 0.4 times as long as median lobe (" puncticeps " species group)............................................................................. 5

5(4). Dorsal surface of head with sparse, wide umbilicate punctures, heterogeneously distributed, with several smooth areas, with three or four punctures on middle part forming two closed rows ( Fig. 2 e). Ventral surface of head with very scarce umbilicate punctures ( Fig. 2 f). Neck with a conspicuous sunken area ( Fig. 2 e). Aedeagus long (length 1.9 mm), parameres 0.27 times as long as median lobe ( Figs. 9 e, 11e)........................................................ T. cribripennis Sharp

5´. Dorsal surface of head with dense umbilicate punctures, separated by one or two times their width, only less dense toward borders, not forming two rows and less wide. Ventral surface of head with umbilicate punctures variably dense, but not as sparse as in previous species. Neck with one or two small sunken areas. Aedeagus median size (length 1.4 mm or less), or if it has similar or more length than T. cribripennis , parameres are less than 0.20 times length of median lobe....................6

6(5). Head long (1.18 times as long as wide), with umbilicate punctures very dense (in contact) both dorsally and ventrally ( Figs. 3 a, b). Neck with two sunken areas (occasionally united by a fine anterior suture) ( Fig. 3 a). Scutellum with four fine punctures.Ventral surface of body darker than in following species. Aedeagus largest, length 3.0– 3.6 mm, with short apical area (0.12 times as long as median lobe) and parameres notably slender, short (0.19 times length of median lobe), each with a small basal tooth ( Figs. 10 a, 11f)............................................................... T. puncticeps Sharp

6´. Head shorter than in T. puncticeps (1.11 times or less as long as wide), dorsal surface with umbilicate punctures moderately to very dense, but on ventral surface are less dense than in previous species ( Figs. 3 c, d, 4). Neck with a long sunken area resulting from faint to clear connection of two small cavities. Scutellum with six to eight fine punctures. Ventral surface of body frequently dark brown to reddish. Aedeagus smaller than in T. puncticeps , with apical area of median lobe and parameres variably developed, parameres without basal tooth..................................................................7

7(6). Dorsal surface of head with umbilicate punctures moderately dense, on denser areas separated by one or two times their width ( Fig. 3 c). Ventral surface of head with scarce umbilicate punctures, leaving wide smooth areas ( Fig. 3 d). Head 1.30 times wider than pronotum, oval shaped, with lateral and posterior borders more convex than in following species ( Fig. 3 c). Aedeagus 1.4 mm of length, parameres slender, with acute apex ( Figs. 9 f, 11g)............................ T. rufipennis Sharp

7´. Dorsal surface of head with very dense umbilicate punctures, in most dense areas they are in contact (Figs. 4a, c). Ventral surface of head with umbilicate punctures from dense to very dense, some of them wider than others, with smooth areas less extended than in previous species (Figs. 4b, d). Head 1.26 times or less as wide as pronotum, oval shaped, with lateral and posterior borders less convex than in T. rufipennis . Aedeagus longer or shorter than in previous species, with wide parameres at least in basal third, and their apex moderately acute ( Figs. 11 h, i)................................................ 8

8(7). Dorsal surface of head with a longitudinal, narrow smooth belt from level of eyes to posterior border (Fig. 4a). Ventral surface of head with dense umbilicate punctures, heterogeneously distributed, but less dense than in T. arizonicus (Fig. 4b). Head almost as long as wide (proportion length/width = 1.06). Neck with two rounded, sunken areas faintly connected by a fine anterior suture (Fig. 4a). Aedeagus small (length 1.2–1.3 mm), with parameres as long as 0.38 times length of median lobe, with internal sac moderately visible, occupying near 2/3 of space of median lobe ( Figs. 9 g, 11h)........... .. T. halffteri Smetana

Figures

FIGURE 2. Thyreocephalus jalapaensis: a) dorsal view of the head and pronotum; b) ventral view of the head (mandibles excluded). Thyreocephalus scutellaris: c) dorsal view of the head and pronotum; d) ventral view of the head (mandibles excluded). Thyreocephalus cribripennis: e) dorsal view of the head and pronotum; f) ventral view of the head (mandibles excluded). Scale = 2 mm.

FIGURE 3. Thyreocephalus puncticeps: a) dorsal view of the head and pronotum; b) ventral view of the head (mandibles excluded). Thyreocephalus rufipennis: c) dorsal view of the head and pronotum; d) ventral view of the head (mandibles excluded). Scale = 2 mm.

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 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 10. Ventral view of the aedeagus of: a) Thyreocephalus puncticeps, b) T. arizonicus (" wrinkled " variation), c) T. arizonicus (normal). Scale = 0.5 mm.

FIGURE 11. Left paramere of the aedeagus of: a) Thyreocephalus unicolor, b) T. sp. aff. subtilis, c) T. jalapaensis, d) T. scutellaris, e) T. cribripennis, f) T. puncticeps, g) T. rufipennis, h) T. halffteri, i) T. arizonicus.