Palaeochiridiinae, Turbanov & Kolesnikov & Vorontsov & Shadrin & Vasilenko & Perkovsky, 2025

Turbanov, Ilya S., Kolesnikov, Vasiliy B., Vorontsov, Dmitry D., Shadrin, Danila S., Vasilenko, Dmitry V. & Perkovsky, Evgeny E., 2025, Palaeochiridiinae subfam. nov. (Arachnida: Pseudoscorpiones: Pseudochiridiidae) from mid-Cretaceous Burmese amber, with a description of new genus and species, Zootaxa 5686 (4), pp. 536-554 : 538-539

Subfamily Palaeochiridiinae subfam. nov.

Type genus. Palaeochiridium gen. nov.

Diagnosis. As for type and only genus.

Remarks. Chamberlin (1923) established the subfamily Pseudochiridiinae Chamberlin, 1923 for the genus Pseudochiridium With, 1906 , then assigned to the family Cheliferidae Risso, 1827 , to show the uniqueness of its morphology within that family. However, the same researcher ( Chamberlin 1931) raised this subfamily to the level of a family, and together with the families Cheiridiidae and Sternophoridae Chamberlin, 1923 placed them in the superfamily Cheiridioidea Hansen, 1894 . Subsequent studies of sternophorid pseudoscorpions ( Murienne et al. 2008; Harvey et al. 2016; Benavides et al. 2019) showed that they are the sister group of Cheiridioidea , thereby reestablishing the clade first identified by Chamberlin (1931) as the superfamily Sternophoroidea Chamberlin, 1923 . Beier (1932) subsequently considered Pseudochiridiidae as a subfamily of Cheiridiidae ; however, Harvey (1992) transferred Cheiridiidae and Pseudochiridiidae to the superfamily Garypoidea Simon, 1879 . Judson (2000) restored Cheiridioidea , indicating various reevaluation of some characters used by Harvey (1992). Thus, at present, the pseudochiridiid pseudoscorpions include only one subfamily— Pseudochiridiinae Chamberlin, 1923 , stat. nov.

The family Pseudochiridiidae has only two genera, Paracheiridium and Pseudochiridium , which differ mainly in the number of visible tergites dorsally (11 tergites in Paracheiridium vs. 10 tergites in Pseudochiridium ) and number of rallum blades (3 blades in Paracheiridium vs. 2 blades in Pseudochiridium ). Vitali-di Castri (1970) and Judson (2007a) such a division seems rather artificial. However, the description of a new subfamily from Burmese amber significantly expands the morphological characteristics of this family.

The new subfamily is assigned to Pseudochiridiidae based on the following characters: carapace with cucullus; abdomen subovate; pseudosternum absent; anal plate surrounded by sternite XI and is subventral; coxa IV much wider than coxa I; galea setae ( gs) of chelicerae subdistal; serrula exterior present, fused; trichobothrium isb on internal face; legs monotarsate; femur and patella of legs fused to form femoropatella; legs all plainly 6-segmented; arolium shorter than claws.

The new subfamily differs from Pseudochiridiinae on the basis of the following characters: carapace trapezoidal with a length to width ratio of more than two ( vs. trianglular with a length to width ratio of less than two in Pseudochiridiinae ); posterior margin of tergites rounded or very weak chevroned ( vs. clearly chevroned in Pseudochiridiinae ); tergites triangular in lateral view ( vs. rounded in Pseudochiridiinae ); setae b of chelicera absent ( vs. present in Pseudochiridiinae ); galea long, twice as short as movable finger of chelicera ( vs. small, ten times or more shorter than movable finger in Pseudochiridiinae ). In addition, the new subfamily has an unusual shape of the trochanter and femur of palp—strongly expanded and flattened, which resembles those of Feaellidae .

The tergites chevroned shape is a unique and easily noticeable apomorphy of Pseudochiridiidae ( Harvey 1992) . However, in Palaeochiridiinae subfam. nov. this character is expressed extremely weakly: only the median tergites have a barely noticeable angle in the medial part, and are almost rounded (plesiomorphy). The presence of a weakly developed apomorphic character is either a result of the primitivism of this character in the family group, or a dead-end return to plesiomorphy, which gives Palaeochiridiinae subfam. nov. an isolated position in the group (obviously a dead-end).

Two other groups of characters can be defined as apomorphies within Pseudochiridiinae , since they are not found in any other representative. However, these characters are found in a completely unrelated group, namely, Feaellidae , so they are obviously homoplasy. These characters include widened trochanter and femur of palp and a strongly elongated carapace. The presence of widened and flattened trochanter and femur of palp, serving as a grasping apparatus, is a unique character of Feaellidae and was not found in any other. It cannot be argued that in Palaeochiridiinae subfam. nov. widening of trochanter and femur of palp serves the same purpose (grasping function), since chela is normally developed and quite mobile in relation to patella, and in addition, the carapace and palps lack specific projections that help to hold prey. But it is obvious that such a strong expansion of the segments played an important functional role. Moreover, the presence of widened trochanter and femur with a large chela has already been observed in a single representative of the subfamily Archaeofeaellinae Kolesnikov, Turbanov, Eskov, Propistsova & Bashkuev, 2022 , which is presumably located in the root group of Feaellidae ( Kolesnikov et al. 2022) . Therefore, we regard this form of palps as homoplasy and a dead-end branch in the family Pseudochiridiidae . The second character—an elongated carapace—is also unique to Feaellidae , namely the fossil subfamily Protofeaellinae Kolesnikov, Turbanov, Eskov, Propistsova & Bashkuev, 2022 . However, unlike Protofeaellinae, Palaeochiridiinae subfam.nov. carapace trapezoidal and among groups with trapezoidal or triangular carapace there are no representatives with such an elongated carapace. Therefore, we also consider this character to be homoplasy.

Based on the presence of a number of significant unique features, some of which are homoplasy, we believe that Palaeochiridiinae subfam. nov. is a separate branch of the Pseudochiridiidae group that did not leave living descendants, significantly different from other representatives of the family.

Etymology. It comes from the name of the subfamily's type genus.

Genus Palaeochiridium gen. nov.

Type species (present designation): Palaeochiridium insolitum gen. et sp. nov.

Diagnosis. Setae of dorsal surfaces large and strongly clavate, with jagged tops; carapace trapezoidal; posterior margin of tergites rounded or very weak chevroned; tergites triangular in lateral view, with setae located along their posterior margin; pedipalpal coxae with strong granulation; coxae of legs I–IV with large, nearlysmooth (microgranulate) areas that lack macrogranules; coxa IV with 42–46 very short setae; tergites not divided; chelicera with 4 simple setae on hand, b absent, ls more than twice longer than es; movable finger smooth and without teeth; galea long, twice as short as movable finger, forked at end; serrula exterior with at least 12–13 blades; rallum of two blades, in distal part with a small tooth in middle; trochanter and femur of pedipalp noticeably widened (2–3 times wider than patella); position of trichobothrium t variable: from proximal to distal st; fixed chelal finger with 21–22 rounded blunt teeth; movable finger with 16–18 teeth, most of which are cuspidate and inclined backwards, with 2–6 rounded blunt teeth at base of finger; venom apparatus present on both chelal fingers.

Etymology. From palaeo- (Ancient Greek πᾰλαιός), a prefix meaning old or ancient, and - chiridium, part of generic names in a family Pseudochiridiidae ; referring to the hypothetical ancient position of the new taxon in the phylogeny of this family. The name is neuter in gender.