Hiemalidactylus eileenae, Schall & Gu & Husemann, 2025

Schall, Ole-Kristian Odin, Gu, Jun-Jie & Husemann, Martin, 2025, Two new members of Tridactylidae (Orthoptera: Caelifera) from mid-Cretaceous Kachin amber, Zootaxa 5693 (2), pp. 168-178 : 173-175

Hiemalidactylus eileenae sp. nov.

Zoobank-ID: urn:lsid:zoobank.org:act:

Figs. 3–4

Etymology: The species is named for Eileen Nguyen from the LIB Hamburg in thanks of her continued help concerning imaging and collection access during the first authors’ doctoral studies and the last authors works.

Locality and horizon: The specimen was included in amber found in Hkamti , Sagaing Division, Myanmar or Tanai, Kachin State Burma, Myanmar, two nearby amber mining locations. The amber from Hkamti is ca. 110 My and the amber from Tanai ca. 99 My old.

Holotype: Sex unknown. Specimen part of the LIB-Hamburg collection; collection number GPIH07247 (ex collection Martin Husemann MH0110).

Diagnosis of species: As for genus (monotypic).

Description: Well-preserved, probably late instar nymph. Only missing distal parts of the left metathoracic leg (right side fully intact).

Measurements (mm): Body length 1.12 (head to abdominal apex; not including cerci or paraproct). Head height 0.4. Compound eye width 0.14. Compound eye height 0.16. Pronotum length 0.32. Pronotum height ca. 0.24. Forewing bud 0.09. Prothoracic leg: tibia 0.34, tarsus 0.12. Mesothoracic leg: tibia length 0.42, tibia width 0.15, tarsus 0.17. Metathoracic leg: Femur length 0.85, femur width 0.25, tibia length 0.81, tibia width 0.05. Tarsus 0.2. Subapical spurs 0.06, apical spurs 0.05. Paraproct ca. 0.2. Basal cercus segment length 0.17. Basal cercus segment width 0.04. Distal cercus segment length 0.05-0.08. Distal cercus segment width 0.01.

Head: With conspicuous coloration of contrasting light and dark areas, including compound eye. Compound eye not protruding, lateral position on head. Antennomeres with short setae.

Thorax: Pronotum without elevation, bearing sparse setae, especially on posterior margin. Forewings present as underdeveloped buds. Hindwings absent.

Legs: Prothoracic leg: Femur rather short. Tibia with setae and three long apical dactyli, the longest of which is 0.04 mm long. Tarsus two-segmented; basal segment shorter than distal segment; distal segment bearing two claws.

Mesothoracic leg: Femur inconspicuous. Tibia distinctly inflated with triangularly shaped extension at widest point on one side. Distal part with setae. Tarsus two-segmented; basal segment shorter than distal segment; distal segment bearing two claws.

Metathoracic leg: Femur apically with few dorsal setae. Inflated along entire length, but still rather slender. Tibia with small denticles placed at a distance along the entire length. Subapical and apical spurs present (only one subapical spur can be seen, apical spurs as pair); approximately of same length. Tarsus much longer than spurs, pointed apically and without hair, spines, or denticular process.

Abdomen: Cerci two-segmented, basal segment longer than distal segment. Tapering consistently without distinct reduction in width from basal to distal segment. Both segments with few setae. Paraproct prominent, narrow triangular, extending far beyond the abdominal apex to almost the length of the basal cercus segment; not setulose. Paraproctal processes absent. Subgenital plate not elongated and not visible.

Remarks: The new species is placed in Tridactylidae based on the distinct inflation of the mesotibia as well as the two-segmented cerci. It is suggested to be part of the subfamily Tridactylinae due to the absence of a subapical denticular process on the metatarsus. Hiemalidactylus can be differentiated from all previously described genera of the family except for Birmitoxya Gorochov, 2010 and Duappendactylus described herein, by the absence of paraproctal processes. From these two genera it can be readily separated by the absence of an elongated subgenital plate. Due to the underdeveloped forewings, as well as the very small body size of Hiemalidactylus eileenae , the specimen is probably a nymph. The classification of nymphs of Tridactylidae is problematic, because very little is known about morphological differences between adult and nymphs of the family ( Baena-Bejarano et al., 2018). However, Gorochov (2010) described Birmitoxya intermedia based on a nymphal specimen and in this species the subgenital plate was clearly visible, suggesting that the absence/presence of an elongated subgenital plate can be used as a diagnostic character even in nymphs of Tridactylidae . Likewise, the presence/absence of paraproctal processes can be used to diagnose nymphal specimens, too, as paraproctal processes - if present in the adults - are usually found in the nymphs as well (see Ellipes deyrupi Woo, 2021 and Ellipes eisneri Deyrup, 2005 in Woo (2021)). In terms of species identification, Baena-Bejarano et al. (2018) considered the coloration pattern a reliable character for associating nymphs with the correct species in Mirhipipteryx pulicaria ( Saussure, 1896) . The likeness of coloration between nymphs and adults of Ellipes deyrupi and Ellipes eisneri is apparent too (see Fig. 2 and 7 in Woo (2021)), although coloration is lighter in the nymphs. Hiemalidactylus eileenae has distinct head coloration which should facilitate species identification once adult specimens are found. The description of this well-preserved individual helps to better understand nymph morphology in Tridactylidae .

Figures

FIGURE 2. Duappendactylus melanocephalus gen. et sp. nov. holotype (sex unknown) GPIH07246. A. and B. Detail of prothoracic leg and metathoracic tibia. Red arrows in A mark dactyli on protibia. Abbreviations: as = apical spurs; sas = subapical spurs; mtta = metatarsus; mtt = metatibia. Scale bars = 0.2 mm. C. and D. Detail of forewing, mesothoracic leg and metafemur. Abbreviations: ce = cerci; fw = forewing; mtf = metafemur; msf = mesofemur; mst = mesotibia. Scale bars = 0.5 mm. E. and F. Detail of abdomen. Abbreviations: pp = paraproct; sgp = subgenital plate; ce = cerci. Scale bars = 0.2 mm.

FIGURE 3. Hiemalidactylus eileenae gen. et sp. nov. holotype (sex unknown; nymph) GPIH07247. A. and C. Specimen, left lateral view. B. and D. Specimen, right lateral view. Scale bars = 1 mm.

FIGURE 4. Hiemalidactylus eileenae gen. et sp. nov. holotype (sex unknown; nymph) GPIH07247. A. and B. Detail of head, thorax and prothoracic leg. Abbreviations: ptl = prothoracic leg; e = eye; pn = pronotum; fw = forewing. Scale bars = 0.5 mm. C. and D. Detail of pronotum and prothoracic leg. Red arrows mark dactyli of protibia. Abbreviations: an = antenna; pn = pronotum; pt = protibia; pta = protarsus. Scale bars = 0.5 mm. E. and F. Detail of mesothoracic leg. Abbreviations: mst = mesotibia; msta = mesotarsus. Scale bars = 0.1 mm. G. and H. Detail of metathoracic leg. Abbreviations: mtt = metatibia; sas = subapical spur; as = apical spurs; mtta = metatarsus. Scale bars = 0.5 mm. I. and J. Detail of abdomen. Abbreviations: pp = paraproct; ce = cerci. Scale bars = 0.1 mm.