Isometrus maculatus (DeGeer, 1778)

Deshpande, Shubhankar, Joshi, Mihir, Kawai, Kazusa, Deb, Arnab, Lee, Jeng-Di, Bastawade, Deshabhushan, Gowande, Gaurang & Sulakhe, Shauri, 2023, Molecular and morphological confirmation of Isometrus maculatus (DeGeer 1778) (Scorpiones Buthidae) from Northeast India and East Asia, Euscorpius 374, pp. 1-19 : 5-10

Isometrus maculatus (DeGeer, 1778)

( Figures 1–25 , Tables 1–2) http: //zoobank. org/urn: lsid: zoobank. org: act: 897D4BDF-

4DD1-47BC-A0B4-004EE28B1745

MATERIAL EXAMINED. India, Tripura, Teliamura, 23.84°N 91.65°E, 70 m a. s. l., leg. Arnab Deb, 9 November 2022, 3♂ (IES 521, IES 522, IES 523) 3♀ (IES 524, IES 525, IES 526). Japan, Haterumajima Island, Okinawa Prefecture, 24.06°N 123.75°E, 14 m a. s. l., leg. Kazusa Kawai, 13 October 2019, 1♀ (IES 585); Shimojishima Island, Okinawa Prefecture, 24.83°N 125.14°E, 10 m a. s. l., leg. Kazusa Kawai, 30 March 2020, 3♀ (IES 582, IES 583, IES 584); Kuroshima Island , Okinawa Prefecture, 24.24°N 124.01°E, 13 m a. s. l., leg. Kazusa Kawai, 21 February 2021, 1♂ (IES 541) 1♀ (IES 542). Taiwan, Cijin Island , Kaohsiung City, 22.61°N 120.26°E, 6 m a. s. l., leg. Jeng-Di Lee, 3 March 2023, 2♀ (IES 580, IES 581) .

DIAGNOSIS. (♂ ♀) Total length 29.68–55.57 mm. Base colouration yellowish brown and variegated with yellowish brown stripes and spots; appendages yellowish with blackish yellow stripes and spots. Basal segments of chelicera yellowish with black reticulation ending anteriorly into blackish transverse patch. Pectinal teeth number 17–20 in both sexes. Median supra-ocular area finely granular. Median ocelli anteriorly situated in the ratio 1:2.0. Promedian carina on pedipalp patella weakly developed. Tergites I–VI with fine granulation, with median carina stronger on posterior region. Colouration ( Figs.3–4 ): Body yellowish brown and variegated with blackish brown stripes and spots; appendages yellowish with blackish brown stripes and spots; dark brownish to blackish last metasomal segment, darker on posterior portion; pedipalp fingers dark blackish to brown with yellow on one third distal portion. Ventral portion yellow anteriorly and light brown posteriorly. Basal segments of chelicera yellowish with black reticulation ending anteriorly into blackish transverse patch. Fingers of chelicera brownish black with tip of fingers black. Telson yellowish brown in color.

Carapace ( Fig. 10, 11 ): Surface of carapace with mixed (coarse and fine) and dense granulation. Carapace without carinae. Median supra-ocular area finely granular. Interocular area with fine and dense granules. A pair of median eyes situated anteriorly in the ratio 1:2.0 (Ratio of median eyes to anterior margin and median eyes to posterior margin). Anterio-lateral ocular tubercle granular with type 5 lateral ocelli. Three pairs of large major ocelli and two small minor ocelli situated behind the major ocelli. Longitudinal furrow shallow anteriorly and deep posteriorly. Anterior margins finely granular. Lateral margins finely crenulated below lateral ocelli. Posterior margin almost entirely smooth.

Chelicerae: Characteristic of the family Buthidae . Basal segments and movable fingers with tuft of short and firm setae on basal and ventral surfaces.

Pedipalp ( Figs. 3–4 , 8–9 , 12–17 ): Femur with five carinae (prodorsal, retrodorsal, promedian, retromedian and proventral). All carinae crenulated. Intercarinal surfaces with coarse and sparse granulation except ventral surface smooth with few fine granules on proximal portions. Patella with seven distinct carinae (dorsomedian, prodorsal, retrodorsal, promedian, retromedian, proventral, retroventral). Promedian carina moderately developed. Intercarinal surfaces weakly and sparsely granular on dorsal surface and smooth on ventral surface. Chela smooth. Movable and fixed fingers with six rows of prolateral and retrolateral denticles in pairs and one additional single row of retrolateral denticles on proximal portion. Fingers slightly scalloped at the base. Trichobothrial pattern of type A, typical for the genus (chela dorsal 12, chela ventral 2, patella dorsal 6, patella retrolateral 7, femur dorsal 7 and femur prolateral 4).

Legs ( Figs. 3–4 , 8–9 ): Femur and patellae carinated. Tibia 3 and 4 without tibial spur. All legs with a pair of pedal spurs. Tarsomere covered with long delicate setae arranged in parallel rows on ventral side. Tarsomere I (basitarsus) with a tuft of short, stout blackish setae on ventral side and a small bulge situated laterally on the proximal portion. Tarsomere II (telotarsus) compressed laterally and ventrally with paired row of short, pointed, anteriorly directed, closely placed setae. Genital operculum ( Fig. 5 ): Wider than long, elliptical, separated with a pair of short male genital papillae.

Pectines ( Fig. 5 ): Basal piece rectangular, notched on anterior median margin. Posterior margin of basal piece curved. Marginal lamella of 3/3 digits and median lamella of 7/6 digits, outer margin armed with a row of stout short red setae and few setae on surface. Fulcra 17/17, very small, roughly triangular, each armed with few short red setae, placed in between adjacent pectinal teeth. Teeth 18/18, strong and stout. Mesosoma ( Figs. 3–4 , 8–9 ): Tergites I–VI with fine granulation. Median carina more strongly developed on posterior side. Posterior and lateral margins granular. Mesosomal tergites V and VI with mixed granulation along margins. Tergite VII granular, narrowed posteriorly, with two pairs of lateral granular carinae. Weak median carina present, more strongly developed on anterior portion. Sternites III–V almost entirely smooth, each with a pair of spiracles. Sternite VI finely granular on lateral portion. Sternite VII granular on lateral portion; two pairs of granular carinae present on two third portion.

Metasoma ( Figs. 3–4 , 8–9 , 18–20 ): All segments longer than wide. Segment I with five pairs of granular carinae (dorsal lateral, lateral supramedian, lateral inframedian, ventral lateral and ventral submedian). Intercarinal surfaces on segments I– IV finely and sparsely granular. Segments II–IV with four pairs of carinae (dorsal lateral, lateral supramedian, ventral lateral and ventral submedian). Lateral supramedian carina and ventral lateral carinae strongly granular on segments II– IV. Dorsal lateral carina on segments I–IV ending in weak tubercles. Intercarinal surfaces almost smooth. Dorsal lateral carina on segments I–IV ending in weak tubercles. Segment V with five carinae (lateral supramedian and ventral lateral pairs and single ventral median). Intercarinal surfaces coarsely to weakly granular; more granular on posterior one third portion. Anal rim weakly granular.

Telson ( Figs. 6–9 , 18–20 ): Telson with slender vesicle. Ventral median carina weakly granular, ending in triangular, subaculear pointed nodule, armed with a pair of minute denticles on inner basal margin. Lateral and ventral intercarinal surfaces weakly granular. Aculeus elongated and moderately curved.

AFFINITIES. Isometrus maculatus differs from all the Indian species of Isometrus based on the following set of morphological characters:

a. Surface of carapace with mixed (coarse and fine) and dense granulation ( Figs 10, 11 ) as opposed to coarse and dense granulation in I. tamhini and I. wayanadensis ; coarse and sparse granulation with some areas without granules in I. sankeriensis and I. thurstoni ; granular throughout with mixed granules, more densely granular in interocular area and median posterior ocular area in I. kovariki .

b. Spiniform granules of promedian carina of pedipalp patella weakly developed ( Fig. 14 ) as opposed to moderately developed in I. tamhini , I. amboli , I. sankeriensis and I. kovariki ; strongly developed in I. thurstoni , I. wayanadensis , I. longitelson .

c. Mixed granulation on mesosomal tergites V and VI along the margins as opposed to coarse granulation in I. tamhini , and I. longitelson ; fine granulation along margins in I. wayanadensis , I. nakshatra , I. sankeriensis , I. amboli , I. thurstoni and I. kovariki .

d. Ventral median carina of telson vesicle weakly granular ( Fig. 6 ) as opposed to moderately granular in I. amboli , I. wayanadensis ; strongly granular in I. tamhini .

e. Chela length to width ratio in males 7.5–10.4 as opposed to 6.1–6.5 in I. tamhini , 5.3–5.9 in I. amboli ; 5.7–5.8 in I. sankeriensis , 5.1–6.4 in I. kovariki , 5.0–5.2 in I. thurstoni , 5.0–5.3 in I. wayanadensis , 10. 6 in I. nakshatra and 5.0–5.4 in I. longitelson ; in females 5.6–6.3 as opposed to 4. 8 in I. kovariki ; 4.8–5.5 in I. thurstoni ; 4.8–5.0 in I. wayanadensis ; 5.0–5.4 in I. longitelson ( Table 1, 2).

f. Metasomal length to carapace length ratio 7.4–8.2 in males as opposed to 8.8–9.1in I. tamhini ; 6.5–7.3 in I. kovariki , 5.3– 5. 8 in I. nakshatra , 6.8–7.2 in I. wayanadensis and 8.2–8.9 in I. longitelson ( Table 1, 2).

g. Telson vesicle length to depth ratio in males 2.1–2.8 ( Figs. 6, 7 , 18–20 ) as opposed to 2.0–2.4 in I. kovariki , 2.3–2.4 in I. wayanadensis and 3.5–3.7 in I. longitelson ( Table 1, 2).

Molecular analysis

Molecular phylogenetics ( Figs. 24 , 25 ). All known species of the genus Isometrus found in India and Sri Lanka were included in our phylogenetic analyses along with I. maculatus from Northeast India, Japan and Taiwan of a 525 bp fragment of the COI gene. Maximum Likelihood and Bayesian Inference analyses generated trees with different topologies, but I. maculatus from Sri Lanka, India, Japan and Taiwan in both these analyses were recovered as monophyletic. I. maculatus was recovered as sister to I. nakshatra in ML analysis with ultrafast bootstrap support (bp) of 46 and was recovered as sister to I. longitelson in BI analysis with posterior probability (pp) values of 0.65. The low support values in ML and BI analyses could be attributed to the use of a single mitochondrial marker.

Genetic distance (p-distance) (Appendix 1)

I. maculatus was found well separated from all congeners based on a 525 bp fragment of the COI mitochondrial gene. It was recovered as nearest to I. wayanadensis but can be separated with a minimum divergence of 12.6% and a maximum divergence of 13.7%. The maximum intra-specific divergence within I. maculatus was recovered as 3.6%.

Distribution and Ecology

I. maculatus from Teliamura, Tripura, India was only observed on the trees with money plants coiled around the bark ( Fig. 22, 23 ). Intriguingly, such trees were only found near human settlements where the individuals were observed, photographed and collected. The rigorous surveys conducted in the forested areas in Tripura did not yield any different species of Isometrus . In Nansei Islands of Japan, I. maculatus was only found where the minimum temperature is higher than 10˚C ( Kawai, 2021).

Figures

Figure 24. Maximum Likelihood phylogenetic tree (ML) for Isometrus. Values along the nodes are ultrafast bootstraps for 1000 iterations. The lineage in red indicates Isometrus maculatus.

Figure 25. Bayesian phylogenetic tree for Isometrus. Values along the nodes are Bayesian posterior probabilities for Bayesian Inference. The lineage in red indicates Isometrus maculatus DeGeer, 1778.

Figures 1–2. Figure 1. Isometrus maculatus, male, IES-522, from Teliamura, Tripura, India in vivo habitus. Figure 2. Isometrus maculatus, female, IES-525, from Teliamura, Tripura, India in vivo habitus with newborns. Photos taken by Arnab Deb.

Figures 3–7. Isometrus maculatus, male, IES-522, from Teliamura, Tripura, India, dorsal (3) and ventral (4) views, sternopectinal area (5), telson lateral (6) and ventral (7) views. Scale bars = 5 mm (3– 4); 2 mm (5–7).

Figures 8–11. Isometrus maculatus, male, IES-522, from Teliamura, Tripura, India, dorsal (8) and ventral (9) views under UV light, carapace under white light (10), carapace under UV light (11). Scale bar = 5 mm (8, 9).

Figures 12–17. Isometrus maculatus, male, IES-522, from Teliamura, Tripura, India, Pedipalp chela dorsal (12) and ventral (13) views, patella dorsal (14) and external (15) views, femur dorsal (16) and internal (17) views. Trichobothrial pattern indicated by yellow circles. Scale bars = 1 mm.

Figures 18–21. Isometrus maculatus, male, IES-522, from Teliamura, Tripura, India, metasoma in dorsal (18), lateral (19) and ventral (20), movable finger under UV light (21), Scale bars = 5 mm (18–20); 2 mm (21).

Figures 22–23. A tree on which individuals of Isometrus maculatus were observed in Teliamura, Tripura, India.