Chaerilobuthus serratus Lourenço, 2016

Xuan, Qiang, Prendini, Lorenzo, Engel, Michael S., Cai, Chenyang & Huang, Diying, 2025, Extinct scorpion family Chaerilobuthidae from Mid-Cretaceous Burmese amber reinterpreted as subfamily of extant family Pseudochactidae (Chelicerata: Scorpiones), Zoological Journal of the Linnean Society 203 (1), pp. 1-60 : 39-45

Chaerilobuthus serratus Lourenço, 2016

( Figs 32–39 )

Chaerilobuthus serratus Lourenço, 2016: 72–74 , figs 14, 17–19.

Type material: Holotype: one juv. (sex unknown) (Geologisch-Paläontologisches Institut, University of Hamburg, Germany: 11037-2 GPIH4567), Cretaceous (Cenomanian) burmite: MYANMAR: Kachin State (precise locality unknown).

Diagnosis: The following combination of characters is diagnostic for C. serratus : carapace anteromedian margin aligned with anterolateral margins ( Figs 33A , 34A , 37A ); lateral ocelli not protruding, macular ( Figs 34A, C , 37C ); pedipalp chela slender, ratio of chela length: chela manus width greater than 4 ( Figs 35A, E , 38 ); pectines each with five teeth ( Figs 34G , 37H ); ratio of metasomal segment IV: segment V length less than 2 ( Figs 33I, J , 37G ); metasomal segment V dorsosubmedian carinae distinctly serrate ( Fig. 32I, J ); telson vesicle slightly elongated, not bulbous, aculeus relatively long and moderately curved, base narrow ( Figs 33I, J , 37I ).

Description: Based on the material examined ( NIGP 200656, 201163).

Carapace: Posterior width less than length (L/ PW = 1.19 or 1.24, Appendix 2). Anteromedian depression narrow, shallow; anterosubmedial depressions absent; lateral ocular carinae distinct; posteromedian and posteromarginal sulci distinct; surfaces almost smooth to sparsely and finely granular ( Figs 32A , 33A , 34A , 37A ). Median ocular tubercle situated anteromedially; median ocelli absent; one pair of large posterolateral major lateral ocelli present.

Coxosternal region: Surface smooth, sparsely covered in macrosetae ( Figs 33B , 34D , 37F ). Leg I maxillary lobes (coxapophyses) distal margins not rounded, slightly dilated anteriorly and adorned with serrula comprising 13 or 14 denticles ( Fig. 39A ). Sternum pentagonal; lateral margins sublinear, parallel; ventral surface flat, without distinct concave region or median sulcus; posteromedian depression wide, shallow ( Figs 32B , 33B , 34D , 37F ).

Chelicerae: Fixed finger and manus, prolateral and ventral surfaces each with numerous long, dense macrosetae ( Figs 34B , 37B ). Cheliceral dentition partly visible, moveable finger with long dorsal distal (dd) denticle, long ventral distal (vd) denticle, and three or four small ventral accessory (va) denticles; fixed finger with long distal denticle. Moveable finger with prominent serrula, comprising short spinules in proximal two-thirds.

Pedipalps: Segments gracile; surfaces sparsely covered by short microsetae and few macrosetae ( Figs 35A, E , 38B, E ). Femur with four carinae evident; prodorsal and proventral carinae obsolete, crenulate; retrodorsal and retroventral carinae smooth, costate; ventral surface sparsely and finely granular ( Figs 35C, G, I, J , 38A, F, I ). Patella with five carinae evident; prodorsal carina obsolete, comprising several tubercles; prolateral surface, dorsoventral ‘vaulted’ projection (‘anterior process’) moderately developed with prominent pair of apophyses or tubercles (‘patellar spurs’), each possessing one macroseta; retrodorsal and retroventral carinae smooth, costate ( Figs 35A, D, E, H , 38C, G, J ). Chela relatively slender (CL/ CW = 4.94–5, Appendix 2); manus globose; chela with six carinae evident; digital carina complete, distinct, granular medially, becoming costate proximally and distally; dorsomedian carina reduced to few granules at base of fixed finger, becoming obsolete proximally on manus; prodorsal, promedian, and proventral carinae obsolete, each comprising few isolated granules; retroventral carina distinct, disjunct proximally; dorsal secondary, subdigital, retromedian, and ventromedian carinae absent or obsolete ( Figs 35A, B, E, F , 38D, H, K ). Chela finger dentition partly visible, fixed and moveable fingers median denticle rows each comprising oblique, slightly imbricate subrows of c. 12 denticles (first subrow with five denticles), separated by large, serrate prolateral and retrolateral denticles ( Fig. 33C ). Trichobothrial pattern Type D, β configuration ( Figs 35 , 38 ). Femur with 10 trichobothria, four d, three i, and three e trichobothria; trichobothria d 1, d 2, d 4, and d 6 noticeably smaller than others (‘petite’); trichobothrium e 1 situated proximal to trichobothrium d 3; trichobothrium e 3 situated dorsal to trichobothrium d 6 ( Fig. 35A, C, E, G, I, J ). Patella with 10 trichobothria, including three d, one i, and six e trichobothria; trichobothrium i 1 situated distal to trichobothrium d 3 ( Fig. 35A, D, E, H ). Chela with 12 trichobothria; fixed finger with three i, two e, and two d trichobothria; manus with four E and one V trichobothria; trichobothrium Et 1 situated distally on manus, almost aligned with or proximal to moveable finger condyle; trichobothrium eb situated on fixed finger, slightly distal to moveable finger condyle; trichobothrium esb situated medially on fixed finger; trichobothrium V 2 situated distally on manus near retroventral carina; macroseta situated medially on manus and near retroventral carina ( Fig. 35A, B, E, F ).

Legs: Tibia lateral and ventral surfaces each with scattered macrosetae ( Figs 33D, G, H, K , 37D ). Basitarsi each with pair of spinule rows, comprising 10–13 relatively short spinules, distally ( Fig. 34I–L ). Telotarsi each with slightly irregular pair of ventrosubmedian spinule rows, comprising relatively long spinules ( Fig. 33K, L ). Ungues moderately long, distinctly curved; dactyl pronounced, pointed ( Figs 34I–L , 37D ).

Pectines: Basal piece long, narrow with shallow median sulcus ( Figs 33B , 34D , 37H ). Three marginal lamellae and four median lamellae; surface sparsely covered in macrosetae; longitudinal suture between marginal and median lamellae distinct ( Figs 33B , 34G , 37H ). Fulcra absent or obsolete. Teeth rounded, distal three-quarters of each tooth occupied by sensillar field; peg sensilla relatively long, columnar ( Fig. 34G , 37H ).

Genital operculum: Two opercular sclerites narrow and completely separated, as long as pectinal plate ( Figs 33B , 34D , 37F ).

Mesosoma : Pretergites surfaces almost smooth ( Figs 33A, E , 37E ); post-tergites I– VI surfaces finely granular, acarinate ( Fig. 34E , 37E ); tergite VII surface sparsely granular with four serrate carinae (paired dorsosubmedian and dorsolateral carinae) in posterior half of segment ( Fig. 34H ). Sternites surfaces smooth, with scattered macrosetae; posterior margins broadly recurved ( Figs 33F , 34F ); respiratory spiracles (stigmata) small, ovoid to round ( Fig. 34F ).

Metasoma: Segments I– V progressively increasing in length, I wider than long, others longer than wide ( Figs 33I, J , 34H , 37G ). Segments I– V lateral and ventral surfaces each with few, short macrosetae; I– III dorsal surfaces each with distinct depression. Segment I with six distinct carinae (paired dorsosubmedian, dorsolateral, and ventrolateral carinae), segments II – V each with eight distinct carinae (paired dorsosubmedian, dorsolateral, ventrolateral, and ventrosubmedian carinae); dorsosubmedian carinae distinct on all segments, serrate throughout length, converging posteriorly; dorsolateral carinae distinct, serrate on segments I– III, smooth, costate on IV and V; ventrolateral carinae obsolete on segments I and II, distinct, slightly granular on III – V; ventrosubmedian carinae absent on segment I, obsolete on II and III, distinct, serrate on IV and V.

Telson: Vesicle elongate; dorsal surface relatively smooth; lateral and ventral surfaces finely and densely granular; ( Figs 33I, J , 37I ); ventral surface with several macrosetae; subaculear tubercle absent; prominent subaculear setal pair. Aculeus moderately long, shallowly curved; base moderately wide, less than half vesicle width.

Material examined: MYANMAR: Kachin State: Noije Bum near Hukawng Valley, precise locality unknown, Cretaceous (Cenomanian) burmite: two juv. (sex unknown) ( NIGP 200656 , 201163 ) .

Figures

Figure 32. Chaerilobuthus serratus Lourenço, 2016, one juv.(NIGP 200656), habitus under incident light.A, dorsal aspect.B, ventral aspect. Scale bars: 1 mm.

Figure 33. Chaerilobuthus serratus Lourenço, 2016, 1 juv. (NIGP 200656), morphology under epifluorescence. A, carapace and tergites I–III. B, coxosternal region and pectines, ventral aspect.C, pedipalp chela denticle rows, dorsal aspect. D, leg I tarsus, dorsal aspect. E, tergites III–VII. F, sternites III–VII.G, leg II tarsus, lateral aspect. H, leg III tarsus, lateral aspect. I, J, metasoma and telson, lateral aspect.Scale bars: 400 μm (A, B, E, F, I, J); 200 μm (C, D, G, H, K).

Figure 34. Chaerilobuthus serratus Lourenço, 2016, one juv. (NIGP 200656), morphology under confocal microscopy. A, carapace.B, chelicera, ventral aspect. C, lateral ocelli. D, sternum and genital operculum. E, tergites I–V.F, sternites III–V.G, sinistral pecten, ventral aspect. H, tergites VI, VII, and metasomal segment I, dorsal aspect. I–L, pedipalp chela fingers dentition, lateral aspect. Scale bars: 400 μm (A, D, E, F; H); 100 μm (B, C, G, I–L); 200 μm (M).

Figure 35. Chaerilobuthus serratus Lourenço, 2016, one juv. (NIGP 200656), pedipalp trichobothrial pattern under confocal microscopy (B–D, F–H, J) and epifluorescence (A, E, I). A–D, sinistral pedipalp, dorsal aspect. E–H, sinistral pedipalp, ventral aspect. I, J, dextral femur, dorsal aspect. Scale bars: 400 μm (A, E); 200 μm (B–D, F–J).

Figure 36. Chaerilobuthus serratus Lourenço, 2016, one juv. (NIGP 201163), habitus under incident light. A, dorsal aspect. B, ventral aspect. Scale bars:1 mm.

Figure 37. Chaerilobuthus serratus Lourenço, 2016, one juv. (NIGP 201163), morphology under confocal microscopy. A, carapace.B, chelicera, dorsal aspect.C, lateral ocelli. D, leg III tarsus, lateral aspect. E, tergites. F, coxosternal region.G, metasoma and telson, lateral aspect. H, pectines, ventral aspect. I, telson, lateral aspect. Scale bars: 200 μm (A, E–G); 50 μm (B, H); 100 μm (C, D, I).

Figure 38. Chaerilobuthus serratus Lourenço, 2016, one juv. (NIGP 201163), pedipalp trichobothrial pattern under confocal microscopy (A, C, D, F, G, H, I–K) and epifluorescence (B, E). Scale bars: 100 μm (A, C, D, F–K); 200 μm (B, E).

Figure 39. Scorpion taxa illustrating presence or absence of serrula on maxillary lobes (coxapophyses) of legs I and II under confocal microscopy. A, Chaerilobuthus serratus Lourenço, 2016, one juv. (NIGP 200656).B, Chaerilobuthus enigmaticus Lourenço, 2015, one juv. (NIGP 201158). C, Chaerilobuthus enigmaticus Lourenço, 2015, one juv. (NIGP 201159).D, Chaerilobuthus complexus Lourenço, 2011, one juv. (NIGP 200655). E, Chaerilobuthus knodelorum Lourenço, 2018, one juv. (NIGP 200657).F, Chaerilobuthus gigantosternum Lourenço, 2016, one juv. (NIGP 200654).G, Chaerilobuthus hansgeorgmuelleri Lourenço, 2019, one subad.(NIGP 201164). H, Betaburmesebuthus bellus Lourenço 2016, one juv.(NIGP 200649). I, Chaerilus sp., one juv. (NIGP 180155). Scale bars: 100 μm (A–E, G–I); 50 μm (F).