Pilarta aroma, Pati & Rajesh & Raj & Sheeja & Kumar & Sureshan, 2017

Pati, S. K., Rajesh, L., Raj, Smrithy, Sheeja, V. U., Kumar, A. Biju & Sureshan, P. M., 2017, Karkata, a new genus of gecarcinucid freshwater crab with two new species, and four new species of Pilarta Bahir and Yeo, 2007 and Cylindrotelphusa Alcock, 1909 (Decapoda: Brachyura) from Kerala, India, Journal of Natural History (J. Nat. Hist.) 51 (23 - 24), pp. 1295-1330 : 1310-1314

Pilarta aroma sp. nov.

( Figures 7 (a–i) and 8(a–d))

Type specimens

Holotype: male (cw 19.07 mm, cl 13.53 mm, ch 8.36 mm, fw 5.39 mm), Pongalappara Agasthyamala , Thiruvananthapuram district, Kerala, India (8.616°N, 77.246°E; altitude 1784 m), 1 February 2015, coll. Smrithy Raj (ZSI, WRC-C.1529).

Paratypes: 2 males (cw 18.23–19.72 mm, cl 13.81–14.34 mm, ch 8.05–9.27 mm, fw 5.50–5.53 mm), same data as holotype (ZSI, WRC-C.1530).

Diagnosis

Carapace broader than long (cw/cl = ca. 1.3–1.4), sparsely punctate; dorsal surface convex in frontal view, almost smooth; anterolateral and posterolateral margins glabrous; front slightly broad (fw/cw = ca. 0.3); epigastric cristae visible as 2 low, broad, almost smooth protuberances; postorbital cristae not well developed, smooth; external orbital angle broadly triangular, with long outer margin, ca. 3 times length of inner margin; epibranchial tooth very small, blunt; branchial regions inflated, lacking striae; cervical grooves distinct, broad; H-shaped groove deep; epistome posterior margin with rounded median lobe, distinctly sinuous lateral lobes ( Figure 7 (a,b)). Ambulatory legs with dense setae on external surfaces of dactylus, propodus and carpus ( Figure 7 (a,f)). Sutures between male thoracic sternites s2/s3 and s3/s4 undiscernible as grooves ( Figure 7 (c,g)). Male abdomen broadly T-shaped; sixth abdominal somite distinctly longer than telson; telson broader than long ( Figure 7 (c,h)). G1 terminal segment less stout, slightly long, ca. 0.4 times length of subterminal segment, with almost straight outer margin, tip distinctly narrow, straight or slightly curved outwards; subterminal segment with broad median portion, not as broad as widest part of base, outer margin almost straight ( Figure 8 (a–c)). G2 with long distal segment, ca. 0.5 times length of basal segment ( Figure 8 (d)).

Description of male holotype

Carapace broader than long (cw/cl = 1.4), sparsely punctate; dorsal surface convex in frontal view, smooth; anterolateral surface slightly inflated in frontal view; anterolateral and posterolateral margins glabrous; frontal margin bilobed, slightly broad (fw/cw = 0.3); epigastric cristae visible as 2 low, broad, smooth protuberances; postorbital cristae not well developed, smooth; external orbital angle broadly triangular, outer margin long, ca. 3 times length of inner margin, anterior half of outer margin concave; epibranchial tooth very small, blunt, separated from external orbital angle by distinct cleft; postorbital region gently concave; branchial regions inflated, lacking striae; cervical grooves distinct, broad; epigastric groove short, broad; mesogastric groove shallow, long, broad, bifurcated posteriorly; H-shaped groove distinct, deep; frontal median triangle incomplete, with cristate dorsal margin only, lateral margins not developed; epistome posterior margin with prominent, rounded median lobe, distinctly sinuous lateral lobes ( Figure 7 (a,b)).

Chelipeds unequal, left chela larger; fingers of larger cheliped gaping when fingers closed; outer surface of carpus rugose; major tooth of carpus large, broad, blunt; external surfaces of chelipeds glabrous ( Figure 7 (a,c–e)).

Ambulatory legs long, moderately stout, with distinct setae; p3 longest; external surfaces of dactylus, propodus and carpus with dense setae ( Figure 7 (a,f)).

Sutures between thoracic sternites s2/s3 and s3/s4 undiscernible as grooves ( Figure 7 (c,g)).

Abdomen broadly T-shaped; fifth abdominal somite distinctly broader than long; sixth abdominal somite broader than long, distinctly longer than telson; telson broader than long, apex round; sternoabdominal cavity deep, long, extending up to imaginary line joining median part of cheliped coxae ( Figure 7 (c,h)).

Mandibular palp with 2 segments, terminal segment bilobed. First, second maxillipeds each with long flagellum on exopod. Third maxillipeds cover most of buccal cavity when closed; ischium subrectangular, longer than broad, with almost indistinct median sulcus; merus subrectangular, broader than long; exopod longer than ischium, reaching lower third of merus, lacking flagellum ( Figure 7 (i)).

G1 stout, straight; terminal segment less stout, slightly long, ca. 0.4 times length of subterminal segment, with almost straight outer margin, tip distinctly narrow, slightly curved outwards; subterminal segment with broad median portion, not as broad as widest part of base, outer margin straight ( Figure 8 (a–c)). G2 with long distal segment, ca. 0.5 times length of basal segment ( Figure 8 (d)).

Live colour

Carapace, chelipeds and ambulatory legs are all brown.

Paratypes

The male paratypes (ZSI, WRC-C.1530) resemble the holotype in their overall carapace and gonopod characters. Nevertheless, the paratypes show the following differences: epigastric cristae that are slightly rugose in the smaller male (vs smooth); a median sulcus on the third maxilliped ischium that is distinct (vs indistinct); and a G1 tip that is straight in the smaller male (vs slightly curved outwards in the holotype).

Etymology

‘Aroma’ means ‘hairless’ in Sanskrit. Used as a noun in apposition, alluding to the smooth or hairless carapace and chelipeds of the crab.

Type locality

Pongalappara , Agasthyamala, Thiruvananthapuram district, Kerala, India (8.616°N, 77.246°E; altitude 1784 m) .

Remarks

The new species, Pilarta aroma , is most similar to P. anuka due to its sparsely punctate carapace, glabrous anterolateral and posterolateral margins of the carapace, epistome posterior margin with distinctly sinuous lateral lobes, sixth male abdominal somite longer than telson, male telson broader than long, less stout G1 terminal segment, and comparatively short G2 distal segment, ca. 0.4–0.5 times the length of the basal segment ( Figures 7 (a–c,h) and 8(a–d) for P. aroma ; see Bahir and Yeo 2007, figs 25(a,d,f– h) and 26(a–c) for P. anuka ). However, P. aroma is distinguished from P. anuka by the smooth postorbital cristae ( Figure 7 (a,b)) (vs rugose postorbital cristae; see Bahir and Yeo 2007, figs 25(a) and 26(a,b)), branchial regions lacking striae ( Figure 7 (a)) (vs branchial regions with distinct striae adjacent to lateral margins; see Bahir and Yeo 2007, fig. 26(a)), deep H-shaped groove ( Figure 7 (a)) (vs comparatively shallow H-shaped groove; see Bahir and Yeo 2007, fig. 26(a)), G1 terminal segment relatively long, ca. 0.4 times the length of the subterminal segment, with almost straight outer margin ( Figure 8 (a–c)) (vs G1 terminal segment relatively short, ca. 0.3 times the length of the subterminal segment, with slightly convex outer margin; see Bahir and Yeo 2007, fig. 25 (f,g)), G1 subterminal segment with almost straight outer margin ( Figure 8 (a,b)) (vs G1 subterminal segment with convex outer margin; see Bahir and Yeo 2007, figs 25(f,g)).

Pilarta aroma is very distinct from P. punctatissima sp. nov. in features of the carapace and gonopods: carapace sparsely punctate (vs densely punctate), dorsal surface of the carapace almost smooth (vs smooth except epigastric and postorbital cristae, postorbital region, frontal region and lateral margins), anterolateral and posterolateral margins of the carapace glabrous (vs with dense setae), postorbital cristae smooth (vs rugose), external orbital angle with comparatively short outer margin, ca. 3 times the length of the inner margin (vs with comparatively long outer margin, ca. 4 times the length of the inner margin), branchial regions lacking striae (vs with distinct striae adjacent to lateral margins), H-shaped groove deep (vs relatively shallow), epistome posterior margin with rounded median lobe, distinctly sinuous lateral lobes (vs with broadly triangular median lobe, medially notched lateral lobes), sixth male abdominal somite longer than telson (vs slightly shorter than telson), male telson broader than long (vs as long as broad), G1 terminal segment less stout, relatively long, ca. 0.4 times the length of the subterminal segment, with almost straight outer margin (vs more stout, relatively short, ca. 0.3 times the length of the subterminal segment, with strongly convex outer margin), G1 subterminal segment with almost straight outer margin (vs with convex outer margin), G2 distal segment relatively short, ca. 0.5 times the length of the basal segment (vs relatively long, ca. 0.6 times the length of the basal segment) ( Figures 7 (a–c,h) and 8 (a–d) for P. aroma ; Figures 9 (a–c,h) and 10(a–d) for P. punctatissima ).

Ecological notes

Crabs were collected from underneath cobblestones in a high-altitude mountain stream (2 m wide, up to 1 m deep) with clear, cold water (10 to 20°C).

Geographic distribution

The new species, Pilarta aroma , is known only from the Western Ghats at Agasthyamala (type locality) in Thiruvananthapuram district of Kerala .

Figures

Figure 7. Pilarta aroma sp. nov., holotype male (ZSI, WRC-C.1529). (a) Dorsal view; (b) frontal view; (c) ventral view; (d) left or major cheliped; (e) carpus of major cheliped; (f) right ambulatory leg (p3); (g) anterior thoracic sternites (s1–s4); (h) abdominal somites 4–6 and telson; (i) left third maxilliped. Scale bars: a–c = 10 mm; d, f = 5 mm; e, g–i = 2 mm.

Figure 8. Pilarta aroma sp. nov., holotype male (ZSI, WRC-C.1529). (a) Dorsal view of left G1; (b) dorsal view of left G1 terminal segment; (c) ventral view of left G1; (d) left G2. Scale bars: a, c, d = 1 mm; b = 0.5 mm.

Figure 9. Pilarta punctatissima sp. nov., holotype male (ZSI, WRC-C.1531). (a) Dorsal view; (b) frontal view; (c) ventral view; (d) right or major cheliped; (e) carpus of major cheliped; (f) right ambulatory leg (p3); (g) anterior thoracic sternites (s1–s4); (h) abdominal somites 4–6 and telson; (i) left third maxilliped. Scale bars: a–c = 10 mm; d, f = 5 mm; e, g–i = 2 mm.