Betaburmesebuthus villosus sp. nov.

(Figs 22–26)

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Material. Holotype, NIGP200652, one probable subadult male.

Etymology. The species name derives from the Latin ‘ vill -’, meaning villous, and ‘- osus ’, meaning fully, indicating the fully hairy telson. The name is masculine in gender.

Diagnosis (emended). This new species can be clearly distinguished from other congeners by the following set of characters: 1) anterior margin of carapace with a strongly marked median concavity (Fig. 24A); 2) posterior margin of carapace broadly and gently incurved (Fig. 24A); 3) spiracles slit and not oblique (Figs 24E, 25C); 4) pectines with 15 teeth (Figs 23D, 24B); 5) surface of telson fully covered by fine and hair-like setae, vesicle very elongated, aculeus very long and strongly curved, base of aculeus very wide (Figs 23H, 25J, K); 6) dorsal patellar spur carina with four small tubercles and several spinous granules (Figs 23E, 24G); and 7) Chela manus with three spinous tubercles on internal surface (Fig. 25 F, G); 8) telotarsus with numerous ventrosubmedian setae (Figs 23F, 24I, 25H, I).

Locality and horizon. Noije Bum near Tanai, Hukawng Valley, Kachin State of northern Myanmar; upper Albian to lower Cenomanian (mid-Cretaceous).

Description. Carapace (Fig. 24A). Densely covered by relatively coarse granules, median furrow evident; median eyes partly damaged and probably separated by more than one ocular diameter; some coarse granules surrounding lateral ocelli, PDMi posterodorsal to PLMa, ADMi mixed with coarse granules, not clear (Fig. 25A).

Coxosternal region (Figs 23B, 24C). Lateral margin of sternum very long, and posterior margin of sternum slightly incurved, posterior depression region evident; genital operculum longitudinally divided, surface covered by short setae, wider than posterior margin of sternum, two valves nearly rounded.

Chelicerae. Not visible except distal denticles of movable finger.

Pedipalps. Femur very slender with five carinae (Figs 23D, 24F, 25B): internomedian carina with several strong tubercles; dorsointernal carina well-developed and serratocrenulate; dorsoexternal carina feebly marked with few granules; ventroexternal carina well marked with several small tubercles; ventrointernal carina costate with few granules and incomplete, remarkably, a macroseta evident and situated on distal of ventroexternal carina (Fig. 24F). Patella with seven carinae (Figs 23E, 24G): Dorsal Patellar Spur carina (DPSc) and Ventral Patellar Spur carina (VPSc) well-developed and with several small tubercles; dorsointernal, dorsomedian, ventroexternal and ventrointernal carinae well-developed and costate with some granules; dorsoexternal carina feebly marked with few granules. Carinae on chela not evident; Chela relatively slender (Cl/Cw = 6.98, Table 1); finger dentition exhibiting granule rows and large spiniform accessory granules from lateral view.

Trichobothrial pattern (Fig. 26). Pedipalp femur with 10 trichobothria, 5 dorsal, 3 internal and 2 external trichobothria, trichobothrium d 2 straddling dorsointernal carina and trichobothrium e 1 proximal to trichobothrium d 5. Patella with 13 trichobothria, including 5 dorsal (d 2 petite), 1 internal and 7 external trichobothria; trichobothrium d 3 external or straddling to dorsomedian carina and trichobothrium d 4 external to dorsomedian carina. Fixed finger with 1 internal, 2 external, and 2 dorsal trichobothria observed (trichobothrium et not visible). Chela manus with 4 external and 2 ventral trichobothria observed (trichobothria Et and Esb not visible).

Legs. Trochanter bearing a lateral apophysis (Fig. 23B). Prolateral and retrolateral pedal spurs present on all legs. Tibial spurs well marked (Fig. 25D, E). Ungues moderately long, dactyl pointed (Fig. 25H, I). Tibia and patella with serrated internal carina (Fig. 22).

Pectines (Figs 23B, 24D). Basal piece with an anterior median furrow (Fig. 24D). Pectines partly visible, boundary between marginal lamellae and median lamellae evident, three median lamellae observed, fulcra present; short sensory hairs extending from surface of lamellae. Teeth elongated and terminal one ovoid.

Mesosoma (Figs 23A, 24B). Tergites finely granular, median carina evident on posterior half of all tergites; dorsolateral carinae feebly marked on tergites V and VI; tergite VII with five carinae (Fig. 5A): paired dorsolateral and lateral carinae evident and costate, axial carina reduced to few middle granules. Sternites covered by few fine granules and sparse setae.

Metasoma (Figs 23G, 24H).All segments longer than width and covered by macrosetae ventrally. Segments I– III with week depression dorsally; segments I and II with ten carinae (paired ventromedian, ventrolateral, lateral, dorsolateral, and dorsal carinae); segments III and IV with eight carinae (paired ventromedian, ventrolateral, dorsolateral, and dorsal carinae); segment V with five carinae (single ventromedian carina, paired ventrolateral and dorsolateral carinae); all carinae on segments I–IV distinctly serrated, carinae on segment V costate.

Telson (Figs 23H, 25J, K). Vesicle with relatively smooth ventromedian and ventrosubmedian carinae, a blunt subaculear tuberance observed and subaculear setal pair not evident; vesicle/aculeus juncture very wide and greater than half of vesicle.

Remarks. The most distinguishing characters differentiating the new species from others are the morphology and ornament of telson, the anterior and posterior margins of carapace and the shape of spiracles. However, the strongly marked median concavity on anterior margin of carapace shared by B. bidentatus (Lourenço, 2015a) and the slit spiracles share by B. larafleissnerae (NIGP201155).