Isometrus (Reddyanus) alessandroi, Lourenço & Ythier, 2025

Lourenço, Wilson R. & Ythier, Eric, 2025, A new cave species of Isometrus Ehrenberg 1828 from Myanmar (Scorpiones: Buthidae), Faunitaxys 13 (4), pp. 1-6 : 2-5

Isometrus (Reddyanus) alessandroi sp. n.

(Fig. 1- 9)

ZooBank:https://zoobank.org/ 6F8F95B4-E65F-40EB-A650-FBE0EA362E8F

Holotype, ♂, Myanmar, Kayin State, Hpa-An, Saddan Cave , 250 m, 16.739735° - 097.718175°, about 90 m from cave entry, hidden in wall crevices, 31/VII/ 2015 (Giupponi A. & Kury A. leg.).

Depository. – Type material deposited in the Museu Nacional , Rio de Janeiro, Brazil .

Etymology. – Patronym honours our colleague Dr Alessandro P. L. Giupponi, Fundação

Oswaldo Cruz (Fiocruz), Rio de Janeiro, Brazil, prominent arachnologist and one of the

collectors of the new species.

Diagnosis. – Isometrus species probably of moderate to small size considering that

the holotype is a pre-adult, measuring 17.37 mm. General coloration yellowish to

pale yellow with the presence of several more or less diffuse dark spots. Carinae and granulations moderately to weakly marked. Carapace moderately emarginate, with a weakly shaped angle. Pectines moderately long; pectinal tooth count 14-15 in male.

Pedipalp chela fingers short; dentate margins of fixed and movable fingers with 6-7

almost linear rows of granules. Internal face of pedipalp patella with 4-5 moderate

spinoid granules. Telson moderately to weakly elongated, weakly globular;

subaculear tubercle strongly developed and rhomboid, dorsally with one granule on

each side.

Description based on male holotype (morphometric measurements after the description)

Coloration. – Generally yellowish to pale yellow. Prosoma: Carapace yellowish with two longitudinal spots laterally and one median strip running from the median eyes to the posterior Fig. 1-2. Isometrus (Reddyanus) alessandroi sp. n., margin; presence of a dark inverted triangle running from lateral to median eyes; eyes almost male holotype, habitus. blackish. Mesosoma : Tergites yellow with three longitudinal brownish stripes that continue the

1. Dorsal aspect. 2. Ventral aspect.

3. Metasomal segment V and telson, lateral aspect. 4. Cutting edge of chela movable finger. 5-9. Trichobothrial pattern. 5-6. Chela, dorso-external and ventral aspects. 7. Femur, dorsal aspect. 8-9. Patella, dorsal and external aspects.

median and lateral stripes of the carapace. Metasomal segments yellowish, with some diffuse, brownish spots on segment I-IV; spots better marked on V. Vesicle yellow; aculeus yellowish at base and reddish at tip. Venter yellow all over; pectines paler. Chelicerae yellow with reddish-brown variegated spots; fingers yellow, strongly infuscate, teeth reddish-yellow. Pedipalps yellow, with infuscations on femur, patella and chela; chela fingers reddish-brown; rows of granules on dentate margins of fingers dark reddish. Legs yellow to pale yellow with brownish spots.

Morphology. – Prosoma: anterior margin of carapace moderately emarginate, with a weakly shaped angle. Carapace carinae weakly marked; anterior median and posterior median carinae weakly developed; central lateral carinae inconspicuous. Intercarinal spaces weakly to moderately granular. Median ocular tubercle anterior to the centre of the carapace; median eyes separated by approximately one ocular diameter. Three pairs of lateral eyes. Mesosomal tergites I-VI with a median carina; weak on I, weak to moderate on II-VI. Tergite VII pentacarinate, with lateral pairs of carinae moderate; median carinae present in proximal half, moderately developed. Intercarinal spaces moderately to weakly granular. Sternites III to VI smooth; VII with four weakly marked carinae. Spiracles markedly short. Pectines moderately long; pectinal teeth count 14-15 in male holotype. Metasomal segment I with 10 carinae, crenulate; II to IV with 8 carinae, crenulate; segment V with five carinae; presence of one weak posterior spinoid granule on dorsal carinae of segments II-III. Dorsal furrows of all segments weakly developed, smooth; intercarinal spaces very weakly granular to smooth. Telson moderately to weakly elongated and weakly globular; one vestigial ventral carina; subaculear tubercle strongly marked and rhomboid, dorsally with one granule on each side. Chelicerae with dentition characteristic of buthids (Vachon, 1963); two reduced basal teeth on movable finger. Pedipalps:Femur pentacarinate;all carinae crenulate. Patella with seven carinae, crenulate; dorsointernal carinae with 4-5 weak spinoid granules. Chela weakly crenulated; internal face with a few spinoid granules. Intercarinal spaces moderately to weakly granular. Dentate margins on fixed and movable fingers composed of 6-7 almost linear rows of granules. Trichobothrial pattern type A, orthobothriotaxic (Vachon, 1974); dorsal trichobothria of femur in β (beta) configuration (Vachon, 1975). Legs: ventral aspect of tarsi with a brushlike group of setae. Tibial spurs absent; pedal spurs present and moderately developed on all legs.

Morphometric measurements (mm) of the male holotype.

– Total length 17.37.

– Carapace

length 2.27.

anterior width 1.47.

posterior width 2.14.

– Mesosoma length 4.47.

– Metasomal segments

I: length 1.27; width 1.07.

II: length 1.54; width 0.94.

III: length 1.74; width 0.87.

IV: length, 1.87; width 0.81.

V: length 2.27; width 0.81; depth 0.81.

– Telson length 1.94.

– Telson width 0.74; depth 0.81.

– Pedipalp

femur length 1.87; width 0.67.

patella length 2.21; width 0.87.

chela length 3.41; width 0.81; depth 0.74.

movable finger length 2.14.

Relationships. – In account of its small size, general morphology and pale coloration pattern, Isometrus (Reddyanus) alessandroi sp. n. shows a certain morphological convergence

in relation with I. (R.) schwotti , described from Thailand (and Cambodia).

The new species can, however, be distinguished from this species by a number of features:

(i) a smaller size (considering the holotype is a pre-adult);

(ii) a slightly paler general coloration with dark spots less marked (more diffuse) on carapace and mesosoma;

(iii) different coloration pattern of pedipalp femur and patella;

(iv) telson less elongated and slightly globular, with only one granule on each side of subaculear tubercle, dorsally.

The most important argument however, supporting the description of the new species, is based on its geographical distribution and particularity of its cave environment.