Chaerilobuthus gigantosternum 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 : 26-31

publication ID	https://doi.org/10.1093/zoolinnean/zlae169
DOI	https://doi.org/10.5281/zenodo.14831490
persistent identifier	https://treatment.plazi.org/id/700187A3-FFCC-FFDF-FCA3-FB58B69CFB28
treatment provided by	Plazi
scientific name	Chaerilobuthus gigantosternum Lourenço, 2016
status

Treatment

( Figs 22–24 View Figure 22 View Figure 23 View Figure 24 )

Chaerilobuthus gigantosternum Lourenço, 2016: 68–72 , figs 12, 13, 15, 16.

Type material: Holotype: one juv. (sex unknown) (Geologisch-Paläontologisches Institut, University of Hamburg, Germany: 11037-1 GPIH4566 View Materials ), Cretaceous (Cenomanian) burmite: MYANMAR: Kachin State (precise locality unknown).

Diagnosis: The following combination of characters is diagnostic for C. gigantosternum : carapace relatively long (L/ Pw = 1.25); carapace anteromedian margin slightly convex and anterosubmedian margin slightly concave ( Figs 22A View Figure 22 , 23A View Figure 23 ); carapace posterior margin linear; lateral ocelli not protruding, macular ( Fig. 23A View Figure 23 ); sternum relatively wide; cheliceral moveable finger with distinct serrula; pedipalp chela slender, manus elongate, with ratio of chela length: chela manus width greater than 4 ( Fig. 24 View Figure 24 ); pectines relatively large, each with five teeth ( Fig. 23F View Figure 23 ); ratio of metasomal segment IV: V length less than 2 ( Fig. 23H, I View Figure 23 ).

Description: Based on the material examined ( NIGP 200654). Carapace: Anterior margin of carapace with few, short microsetae; anteromedian depression not visible; anterosubmedial depressions absent; lateral ocular carinae distinct; posteromedian and posteromarginal sulci not distinct; surfaces almost smooth to sparsely and finely granular ( Fig. 23A View Figure 23 ). Median ocular tubercle situated anteromedially; median ocelli absent; one pair of large posterolateral major lateral ocelli present.

Coxosternal region: Surface smooth, sparsely covered in few macrosetae ( Fig. 23B View Figure 23 ). Distal margins of leg I maxillary lobes (coxapophyses) slightly curved and dilate anteriorly, adorned with serrula comprising c. 13 spiny denticles. Sternum pentagonal; lateral margins sublinear, parallel, ventral surface flat, without distinct concave region or median sulcus;posteromedian depression wide, shallow.

Chelicerae: Fixed finger and manus, prolateral and ventral surfaces each with numerous macrosetae. Cheliceral dentition partly visible, moveable finger strongly overlapping fixed finger; moveable finger with long dorsal distal (dd) denticle, small dorsal subdistal denticle, stout dorsal median denticle and long ventral distal (vd) denticle; fixed finger with long distal denticle. Moveable finger with prominent serrula, comprising c. 10 long spinules and extending almost entire length of ventral surface ( Fig. 23C View Figure 23 ).

Pedipalps: Segments gracile ( Figs 22 View Figure 22 , 23 View Figure 23 ). Femur with three carinae evident; prodorsal, proventral and retrodorsal carinae distinct, smooth and costate. Patella with three carinae evident; retroventral carinae distinct, smooth and costate; prolateral surface, dorsoventral ‘vaulted’ projection (‘anterior process’) distinct, with obsolete pair of apophyses or tubercles (‘patellar spurs’), each possessing one macroseta. Chela relatively slender (CL/ CW = 4.37, Appendix 2); manus elongate; chela with three carinae evident; digital carina complete, distinct, granular medially, becoming costate proximally and distally; prodorsal carina distinct, smooth; retroventral carina obsolete, smooth and costate; other carinae absent or obsolete. Chela finger dentition not visible. Trichobothrial pattern Type D, β configuration ( Fig. 24 View Figure 24 ). Femur with 10 trichobothria visible, five d, three e, and two i trichobothria, trichobothrium e 1 situated proximal to trichobothrium d 3; trichobothrium e 3 situated dorsal to trichobothrium d 6. Patella with eight trichobothria visible, including three d, one i, and four e trichobothria; trichobothrium i 1 situateddistaltotrichobothrium d 3.Chelawith 12trichobothria visible; fixed finger with two d, two e, and three i 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 and near retroventral carina.

Legs: Tibial lateral and ventral surfaces each with scattered macrosetae ( Fig. 23J, K View Figure 23 ). Basitarsi each with pair of spinule rows, comprising c. 12 relatively long spinules, distally. Telotarsi each with slightly irregular pair of ventrosubmedian spinule rows, comprising relatively long spinules. Ungues moderately long, distinctly curved; dactyl pronounced, pointed.

Pectines: Basal piece not visible. Three marginal lamellae and four median lamellae; surface sparsely covered in macrosetae; longitudinal suture between marginal and median lamellae distinct ( Fig. 23E, F View Figure 23 ). Fulcra absent or obsolete. Teeth rounded, distal three-quarters of each tooth occupied by sensillar field; peg sensilla very long and columnar.

Genital operculum: Opercular sclerites not visible.

Mesosoma : Pretergites surfaces almost smooth ( Fig. 23D View Figure 23 ); post-tergites I– VI surfaces finely granular,acarinate ( Fig.23D View Figure 23 ); tergite VII surface sparsely granular with four carinae (paired dorsosubmedian and dorsolateral carinae) in posterior half of segment ( Fig. 23D View Figure 23 ). Sternites surfaces smooth, with scattered macrosetae; respiratory spiracles (stigmata) small, ovoid to round ( Fig. 23E View Figure 23 ).

Metasoma: Segments I– V progressively increasing in length, I wider than long, others longer than wide ( Fig. 23H, I View Figure 23 ). Segments I– V lateral and ventral surfaces each with few, short macrosetae; I– IV dorsal surfaces each with distinct depression. Segments I– III each with six distinct carinae (paired dorsosubmedian, dorsolateral, and ventrolateral carinae), IV and V each with eight distinct carinae (paired dorsosubmedian, dorsolateral, ventrolateral, and ventrosubmedian carinae); dorsosubmedian and dorsolateral carinae distinct, slightly serrate; ventrolateral carinae distinct, costate-granular; ventrosubmedian carinae obsolete.

Material examined: MYANMAR: Kachin State: Noije Bum near Hukawng Valley, precise locality unknown, Cretaceous (Cenomanian) burmite: first instar juv. (sex unknown) ( NIGP 200654 View Materials ). Hypothesized to be in first instar based on small size and weak development of carinae and sulci .