Chthonius halberti Kew, 1916

Gardini, Giulio, 2021, The Italian species of the Chthonius ischnocheles group (Arachnida, Pseudoscorpiones, Chthoniidae), with reference to neighbouring countries, Zootaxa 4987 (1), pp. 1-131 : 57-60

Chthonius halberti Kew, 1916

( Figs 158–172 , 412 )

Chthonius halberti Kew, 1916: 77 , fig. 3.

Kewochthonius halberti: Muchmore 1968: 71 , figs 1–3.

Chthonius (C.) halberti: Judson 1990: 598 , fig. 11.

Type locality: Ireland, Dublin County, Malahide (53°27’N, 6°09’E) .

Distribution. Ireland, United Kingdom, Portugal, France, Italy.

Diagnosis (♂ ♀). A microphthalmic epigean Chthonius that differs from other species of the ischnocheles group in the following combination of characters: anterior margin of carapace without preocular microsetae; posterior margin of carapace with 6 (rarely 5–8) macrosetae; anterior eyes with flat lens; chelicerae without lateral microsetae; chela length 0.505–0.62 mm; movable chelal finger length 0.34–0.41 mm; chelal fingers with contiguous teeth; movable chelal finger with coupled sensilla pc not on a tubercle.

Material examined. FRANCE — Haute-Corse — 2 ♀, Aleria, Étang de Diana, 1 m a.s.l., 1.IX.2019, A. Marata leg.

ITALY — Liguria: Imperia Prov . — 2 ♂ 7 ♀ 1 T, Ventimiglia, Mortola Inferiore, Punta Barbantò , 0 m a.s.l., 13. V.2019, P. Gardini & C. Giusto leg. , Posidonia oceanica banquette. Lazio: Rome Prov . — 1 ♂, Civitavecchia , La Frasca, 0 m a.s.l., 21.I.2008, S. Paribelli & E. De Matthaeis leg. , Posidonia oceanica banquette; 5 ♂ 7 ♀ 1 T, id., 28. V.2008, S. Paribelli & E. De Matthaeis leg. , Posidonia oceanica banquette; 2 ♂ 1 T, id., 20. VIII.2008, S. Paribelli & E. De Matthaeis leg. , Posidonia oceanica banquette; 2 ♂, id., 21.XI.2008, S. Paribelli & E. De Matthaeis leg., Posidonia oceanica banquette. Sicily: Messina Prov . — 1 ♀, Isola di Salina , 7.IV.1990, R. Argano leg. Sardinia: Sassari Prov . — 2 ♂, Palau, near Isuledda , 0 m a.s.l., 15.IV.2000, V. Cottarelli leg. , researching phreatic fauna.

Description of adults (♂ ♀). Integument slightly pigmented, carapace, tergites, chelicerae and pedipalps reddish-brown; hispid granulation on lateral surfaces of carapace, on cheliceral palm, on base of fixed and movable chelal fingers and on dorsal surface of chelal hand. Carapace ( Fig. 160 ) nearly square, 0.9–1.0 times longer than broad, slightly constricted posteriorly; anterior margin between median macrosetae with a widely prominent epistome in both sexes ( Figs 158–159 ); ocular area as in fig. 160, anterior eyes with flat lens (diameter 0.025 –0.035 mm), posterior eyes seeming absent, but all eyes with tapetum; distance from anterior eyes to anterior margin of carapace 0.030 –0.035 mm; standard chaetotaxy 4:6:4:2:6(22), rarely posterior margin of carapace with 5, 7 or 8 setae; lateral setae of posterior margin variable in length, from one third to equal length of the median ones; length of anteromedian macrosetae 0.065 –0.075 mm; setae mainly thick. Standard chaetotaxy of tergites 4:4:6:6:8:8:8:6:1 T2T1:4:1T2T1:0, rarely tergite I 5, II 5–6, III 5, IV 7–9, V 7, VI 6–7 or 9, VII 7 or 9, VIII 7–9, X 5 setae. Chaetotaxy of sternites 9–10:(3)8–10(3):(2)6–8(2):9–11:9–10:8–10:8–10:8–10:2T1T2:0:2; genital opening of males flanked by 6–7 setae on each side. Chelicerae ( Fig. 161 ) 1.9–2.1 (♂ ♀) times as long as broad, palm with 6 (rarely 7) setae, without lateral microsetae; fixed finger with 6–8 teeth, of which the distal last but one larger; movable finger with an isolated subapical tooth (di) more proximal with respect to the spinneret, a large distal tooth and 5–7 teeth proximally reduced in size; gs ratio 0.58–0.70; spinneret weakly raised both in males and females ( Figs 161–162 ); rallum with 11 blades; serrulae interior and exterior with 12–13 and 14–16 blades respectively. Coxal setae: pedipalp 5 (including 2 on manducatory process), I 3 + 3 marginal microsetae, II 4(5), III (5)6(7), IV 7; coxa II with 5–11 coxal spines, coxa III with 3–4 (rarely 6) coxal spines; intercoxal tubercle bisetose. Pedipalp: femur 4.0–4.25 (♂ ♀) times as long as broad, femoral chaetotaxy 3:6:2(3):5(6):1; chela ( Figs 165, 169 ) 4.8–5.0 (♂) or 4.7–4.8 (♀) times as long as deep; hand of chela 1.6–1.75 (♂) or 1.6–1.7 (♀) times as long as deep, short ovoid in dorsal view ( Figs 163–164 ); fixed chelal finger with 58–66 contiguous teeth, tall and rectangular in the distal half of the finger, apically rounded in the proximal half of the finger ( Figs 166–168, 170–172 ); all teeth with dental canal; base of fixed chelal finger with 3–4 microtubercles; fixed finger at level of est-it with 10 teeth occupying 0.05 mm, distance between successive apices 0.005 mm; tip of fixed chelal finger with apical sensilla af 1- 2, distal paraxial seta slightly sinuous and thin; movable chelal finger with 49–58 contiguous teeth, rectangular in the distal half of the finger, apically rounded in the proximal half of the finger and increasingly reduced towards finger base, reaching back near b, all teeth with dental canal ( Figs 166–168, 170–172 ); movable finger at level of st-t with 9 teeth occupying 0.05 mm, distance between successive apices 0.006 mm; position of coupled sensilla pc variable, from proximal sb to distal of sb; tip of movable chelal finger with apical sensilla am 1- 2; trichobothria as in figs 165, 169; ratio sb -st/sb -b = 1.5–1.7; ratio of movable finger/hand of chela 1.85–2.0 (♂ ♀); ratio of pedipalpal femur/movable finger 0.95–1.0 (♂ ♀); ratio of pedipalpal femur/carapace 1.05–1.1 (♂ ♀).

Measurements (in mm). Body length 1.0–1.3 (♂ ♀). Carapace 0.30–0.34 × 0.31–0.36 (0.29–0.33 anteriorly) (♂) or 0.32–0.36 × 0.32–0.39 (0.31–0.37 anteriorly) (♀). Chelicerae 0.275–0.31 × 0.135 –0.155 (♂) or 0.285–0.34 × 0.145–0.18 (♀); movable finger length 0.14–0.155 (♂) or 0.14–0.165 (♀). Pedipalp: femur 0.32–0.36 × 0.075–0.09 (♂) or 0.34–0.40 × 0.08–0.095 (♀); chela 0.505–0.58 × 0.105 –0.115 (♂) or 0.52–0.62 × 0.11–0.13 (♀); hand length 0.17–0.20 (♂) or 0.175–0.22 (♀); movable finger length 0.34–0.38 (♂) or 0.34–0.41 (♀).

Description of tritonymph. Integument with weak pigmentation, hispid granulation less marked than in adults. Carapace 0.95–1.0 times longer than broad, form of anterior margin and eyes as in adults (tapeta not visible); chaetotaxy 4:6:4:2:6(22), tritonymph from La Frasca with 4 setae on posterior row; length of anteromedian macrosetae 0.045 –0.050 mm. Chaetotaxy of tergites I–VIII: 4:4:5:6:6–7:6–7:6:6. Chaetotaxy of sternites II–VIII 5–6:(2)8(2):(1)6(1):10:8:8:8. Chelicerae 2.0–2.05 times as long as broad, palm with 5 setae, without lateral microsetae; fixed finger with 4–6 teeth, proximally reduced in size; movable finger with an isolated subapical tooth (di) and 6 teeth; gs ratio 0.62–0.63; spinneret as in females. Coxal setae: pedipalp 5 (including 2 on manducatory process), I 3 + 2 marginal microsetae, II 4, III 5, IV 5; coxa II with 6 coxal spines, coxa III with 3 coxal spines; intercoxal tubercle bisetose. Pedipalp: femur 3.7–3.8 times as long as broad, femoral chaetotaxy 3:5:2:5:1; chela 4.5–4.9 times as long as deep; hand of chela 1.65–1.85 times as long as deep; fixed chelal finger with 46–56 contiguous teeth, all with dental canal; movable chelal finger with 40–48 teeth, reduced in size towards finger base, reaching back near b; coupled sensilla pc nearer to b than to st; ratio of movable finger/hand of chela 1.7–1.8; ratio of pedipalpal femur/movable finger 0.95; ratio of pedipalpal femur/carapace 0.9–1.0.

Measurements (in mm). Body length 0.7–0.8. Carapace 0.25–0.265 × 0.25–0.28 (0.235–0.26 anteriorly). Chelicerae 0.215–0.23 × 0.105 –0.115, movable finger length 0.10–0.11. Pedipalp: femur 0.23–0.26 × 0.06–0.07; chela 0.37–0.41 × 0.075–0.09; hand length 0.14–0.15; movable finger length 0.24–0.27.

Remarks. Among the species of the Chthonius ischnocheles group, C. halberti is morphologically similar to the epigean C. jonicus , that also occurs in central Italy, Sicily and Sardinia, but differs in the following main characters: posterior margin of carapace with 5–8 macrosetae (4 macrosetae in C. jonicus ); chela length 0.505–0.62 mm (0.40–0.51 mm in C. jonicus ); movable chelal finger length 0.34–0.41 mm (0.275–0.34 mm in C. jonicus ); fixed and movable chelal fingers with 58–66 and 49–58 teeth respectively (with 56–58 and 39–49 teeth in C. jonicus ). Moreover, C. halberti is a strictly halophilic species, while C. jonicus is mainly a Mediterranean maquis species.

For a comparison of Chthonius halberti with C. marciai from Sardinia, see Remarks under the latter species.

The above description of Chthonius halberti partially incorporates the ones of Muchmore (1968) and Judson (1990). Two females from England (Axmouth, Devon) studied by Muchmore (1968) are slightly larger than the species examined here: chela length 0.68–0.70 mm, movable chelal length 0.44–0.47 mm.

The fragmentary distribution of Chthonius halberti is undoubtedly due to the lack of targeted searches in supralittoral environments. The only other record from the Mediterranean Sea ( Judson 1990) is from southern France.

Figures

FIGURES 158–164. Chthonius halberti Kew, 1916, La Frasca (Civitavecchia, Roma). 158, male, anterior margin of carapace; 159, female, anterior margin of carapace; 160, male, carapace; 161, male, right chelicera; 162, female, movable finger of right chelicera; 163, male, right chelal hand, dorsal view; 164, female, id.

FIGURES 165–172. Chthonius halberti Kew, 1916, La Frasca (Civitavecchia, Roma). 165, male, right chela, antiaxial view; 166, male, detail of fingers at the chelal tip, antiaxial view; 167, male, detail of fingers at level of trichobothria est-it and st-t, antiaxial view; 168, male, detail of fingers at level of trichobothrium sb, antiaxial view; 169, female, right chela, antiaxial view; 170, female, detail of fingers at the chelal tip, antiaxial view; 171, female, detail of fingers at level of trichobothria st-t, antiaxial view; 172, female, detail of fingers at level of trichobothrium sb, antiaxial view.

FIGURES 410–413. Distribution maps for the Italian species of the Chthonius ischnocheles group. 410, Chthonius caoduroi Callaini, 1987, Chthonius gallettii n. sp., Chthonius inguscioi n. sp., Chthonius marciai n. sp. and Chthonius multidentatus Beier, 1963; 411, Chthonius caprai Gardini, 1977, Chthonius jonicus Beier, 1931 and Chthonius leoi (Callaini, 1988); 412, Chthonius halberti Kew, 1916, Chthonius nicolosii n. sp., Chthonius ressli Beier, 1956 and Chthonius stammeri Beier, 1942; 413, Chthonius horridus Beier, 1934, Chthonius italicus Beier, 1930 and Chthonius lanai n. sp.