Burmadactylus tenuicerci Fan & Gu & Cao 2023, sp. nov.

Burmadactylus tenuicerci sp. nov.

urn:lsid:zoobank.org:act: 0DF8451E-7121-4B2D-9328-64E458B68B8B

Material. Holotype, LNU-22, gender unknown, a nearly complete specimen, including the head, prothoracic leg, mesothoracic leg, metathoracic leg and terminal abdomen. The specimen is in fair condition, covered by a large crack from the head to the end of the abdomen.

Locality and horizon. Hukawng Valley, Kachin Province, Myanmar; lowermost Cenomanian, Upper Cretaceous.

Description. Holotype, LNU-22 (Fig. 1), gender unknown, body 3.12 mm long measured from the head to the abdominal apex; pronotum 0.7 mm long at midline; profemur 0.6 mm long; protibia 0.5 mm long; mesofemur 1.1 mm long; mesotibia1.0 mm long; metafemur 2.1 mm long; metatibia 1.8 mm long. The specimen is in fair condition, covered by a large fissure from the head to the end of the abdomen.

Head. Hypognathous, capsulate; compound eyes large and well developed; ocelli invisible; antennae moniliform, 7 segments visible, flagellomere widening towards apex, inserted beneath the lower margin of the compound eyes (Fig. 1A, D).

Thorax. The thorax dark brown; pronotum large, shield-like, extending posteriorly to entirely cover the metanotum; posterior margin of pronotum broadly rounded; tegmen and hindwing absent (Fig. 1A, D).

Leg. Prothoracic leg brown; profemur slender, distinctly shorter than mesothoracic leg; protibia robust, apex slightly inflated, with a sparse covering of thick setae and four strong teeth; protarsus two-segmented, slender, with second segment longer than first; basitarsus short; apical tarsomere elongate, slightly curved, with two claws. Mesothoracic leg brown; mesofemur slender, curved, over twice as long as the profemur, basally narrow and apically broad, with sparse setae on the ventral margins; mesotibia almost as long as mesofemur, middle inflated, with dorsal and ventral setae; mesotarsus almost identical to the protarsus. Metathoracic leg dark, saltatorial; metafemur slightly longer than abdomen and greatly inflated along its entire length, with prominent dorsal carina; metafemur mostly obscured by cracks, ventral with several irregularly spaced setae (Fig. 1A, D); metatibia slightly shorter than metafemur, very slender, with tiny spines on the dorsal margins, without setae, lacking swimming plates, with two small subapical spurs and longer apical spurs; metatarsus slightly over twice as long as apical spurs, with a subapical denticular process; metatarsus ventral with sparse setae (Fig. 1C, F).

Abdomen. The abdomen dark brown, with sparse and long setae; dorsal of abdomen obscured by cracks; subgenital plate broad, without styli, bearing a marginal fringe of long setae; cercus long, with numerous long setae, two-segmented, the second segment longer and distinctly slender than the first; paraproctal lobe cone-shaped, relatively small, almost the same as the first segment of cercus, covered with sparse setae, one of the setae near the apex thick and long (Fig. 1B, E).

Diagnosis. The new species is similar to Burmadactylus grimaldi Heads, 2009. The major differences are listed in Table 1.

Etymology. The specific epithet is from the Latin ‘tenui’ and ‘cercus’, used to describe the slender and elongated second segment of cercus in Burmadactylus.

Remarks. Owing to the metatarsus of this specimen with a subapical denticular process, it should be assigned in Dentridactylinae Günther, 1979. B. tenuicerci sp. nov. is distinguished from other fossil Dentridactylinae species by presence of small paraproctal lobe which are much longer (as long as the cercus) in other members of the subfamily (Azar & Nel, 2008; Poinar, 2020). This new species can be assigned to Burmadactylus Heads, 2009 by the following characters: paraproctal lobe small, conical shape; swimming plates absent; margin of subgenital plate with long setae; metatarsus slightly over twice as long as apical spurs. The differences between the new species and the type species B. grimaldii Heads, 2009 are demonstrated in the Table 1.