Gastroptychus valdiviae ( Balss, 1913 )

Tiwari, Shivam, Padate, Vinay P. & Cubelio, Sherine Sonia, 2023, Chirostyloid and galatheoid squat lobsters (Decapoda: Anomura) from Andaman and Nicobar Islands, India, with three new species, Journal of Natural History 57 (9 - 12), pp. 520-556 : 523-529

Gastroptychus valdiviae ( Balss, 1913)

( Figures 2 (a), 3, 4, 5, Supplementary Figure S1)

Ptychogaster valdiviae Balss, 1913: 225 (type locality: ′ Valdivia ̍ station 208, SW of Great Nicobar, 6°54´N, 93°28´E, 296 m)

Chirostylus valdiviae: Doflein and Balss 1913: 133 , fig. 3; pl. 17, fig. 1

Gastroptychus valdiviae: Baba 2005: 212 (key to species), 214 (synonymies); Baba et al. 2008: 24 (synonymies)

Material examined

Type material. Syntype male ( PCL 11.5 mm, CW 7.5 mm) ( ZMB 17479 ), ′ Valdivia ̍ stn 208, SW of Great Nicobar , 296 m depth, 7 February 1899 .

Other material: 1 male (6.0 mm PCL, 4.2 mm CW) (IO/SS/ANO/00127), 2 females (3.5, 4.1 mm PCL, 2.2, 2.6 mm CW) (IO/SS/ANO/00128), south-eastern Bay of Bengal , off Car Nicobar Island, FORVSS stn 355II02, 9.22°N, 92.67°E, 250 m depth, Naturalist ̍s dredge, coll . Vimal Kumar K .G., 11 January 2017.

Description

Carapace. PCL 1.4–1.6 times width, dorsal surface spinulose, with 1 pair of large submedian epigastric spines, 5 moderately large spines along midline (including 1 each on epigastric and metagastric regions, 2 on the cardiac region, and 1 on intestinal region); on either side of the midline, small-sized spines including 3 submedian gastric spines, 2 lateral gastric spines, 1 post-cervical spine, 1 cardiac spine, 2 posterior branchial spines. Lateral margin of carapace with irregular longitudinal row of 5 spines increasing in size anteriorly (including 1 anterior branchial, 4–5 posterior branchials). Branchial regions with randomly scattered spinules. Gastric and branchial regions moderately inflated, distinct cervical groove separates gastric region from the anterior branchial and cardiac regions, branchiocardiac groove shallow. Lateral margins gently convex on hepatic region, convex on branchial region, anterolateral spine short, lateral orbital angle blunt ( Figures 2 (a), 3(a,b)). Rostrum spine-like, 0.3–0.4 times as long as PCL ( Figures 2 (a), 3(a,b)), directed dorsad. Pterygostomian flap rounded anteriorly, surface with a few scattered spines ( Figure 3 (b)).

Sternum

Sternal plastron 1.1 times as long as broad, broadened posteriorly. Sternite 3 width half as wide as sternite 7, anterior margin with 4–7 spines, with medially shallow excavations; sternite 4 slightly wider than sternite 5, lateral margin with strong spine, transverse row of 2–3 pairs of submedian spines; sternite 5 with 2 pairs of spinules on anterior margin, 2–3 spinules on lateral margin ( Figure 3 (c)); sternites 6–7 each with 1 or 2 spinules on anterior margin.

Pleon

Tergites 1–5 smooth dorsally, tergite 6 with 1 spine near each lateral extremity; pleura tapering ( Figure 2 (a), 3(a,b, d)). Telson 0.8 times as long as broad, consisting of 2 laterally lobular plates; posterior plate 2.0 times longer than anterior plate ( Figure 3 (d)).

Eyes

Ocular peduncle nearly reaching distal quarter of rostrum, strongly constricted on mesial margin; cornea dilated ( Figure 3 (a,b)).

Antennule

Antennular peduncle article 1 with unequal distal spines ( Figure 3 (e)).

Antenna

Antennal peduncle overreaching eye. Article 2 with small distolateral spine, article 4 unarmed, article 5 length 1.6 times article 4 length (measured along lateral margin), with elongated distoventral spine. Antennal acicle reaching midlength of article 5, slen- der, breadth half that of article 5 ( Figure 3 (e)).

Mxp 3

Endopods slender, bases widely separated; ischium with crista dentata with 23–24 denticles; merus 1.4 times longer than ischium, with distolateral spine; carpus with 3–4 lateral spines; propodus unarmed ( Figure 3 (f)).

P1

Length 4.0 times PCL, subcylindrical, sparsely setose. Ischium dorsal margin with distal spine, ventral margin with 1 spine at midlength ( Figure 4 (a)); merus, carpus and palm with spines in 6, 6 and 5 rows, respectively ( Figure 4 (b–d)). Merus length 1.2 times as long as carpus. Carpus subequal to palm length. Palm 6.3 times as long as wide, 1.6 times dactylus length. Fingers more densely setose than other articles, gaping moderately, tips corneous, fixed finger with subdistal corneous tooth; occlusal margins of fingers dentate, dactylar occlusal margin with 1 proximal tooth, corresponding margin of fixed finger with 2 teeth flanking dactylar tooth ( Figure 4 (e)).

P2–4

Slender, coarsely setose, merus to propodus with extensor and flexor rows of spines. Meri 2.0, 1.4–1.8 and 1.7 times as long as carpi, respectively, with extensor spines larger than flexor spines ( Figure 4 (f, i, l)). Carpi 0.9, 0.8–1.0 and 0.8 times as long as propodi, respectively, in the Indian male specimen, extensor margins with more numerous slender spines than flexor margins ( Figure 4 (g, j, m)). Propodi 3.3, 2.7–3.5 and 3.2 times as long as dactyli, extensor margins with numerous inclined spines, flexor margins with row of 11–14 slender, movable spines, distal 2 paired, subequal, smaller than antepenultimate spine ( Figure 4 (h, k, n)). Dactyli short, terminating in strong corneous spine, preceded by 9 progressively smaller flexor spines ( Figure 4 (o–q)). P2 overreaching P1 carpus.

Distribution

South-eastern Bay of Bengal off the Nicobars, 250–296 m depth ( Balss 1913; present study) ( Figure 1).

Remarks

During this study, we examined digital images of a syntype of Gastroptychus valdiviae ( Balss, 1913) ( ZMB 17479 ), kindly provided by Dr C .O. Coleman . Our specimens differ from this syntype in the presence of 3–4 spines on the maxilliped 3 carpus (vs only 1 spine in the syntype) . Doflein and Balss (1913, fig. 3) reported the presence of 3 carpal spines in their specimen. Gastroptychus valdiviae shares the presence of numerous gastric spines in addition to epigastric spines, and P2–4 propodi being much longer than carpi, with G. sternoornatus ( Van Dam, 1933) from the western Pacific Ocean . The former, however, differs from the latter in the following characters:

(1) Anterolateral angle of carapace rounded and unarmed (vs armed with 1 small but distinct spine in G. sternoornatus );

(2) Pleonal tergite 6 with 1 spine near each lateral extremity (vs unarmed in G. sternoornatus );

(3) Mxp 3 carpus with a few lateral marginal spines other than distolateral one (vs only distolateral spine in G. sternoornatus );

(4) P1 palm 1.6 times as long as fingers (vs 2.0 times in G. sternoornatus );

(5) P2–4 propodi slightly longer than carpi, with 14 movable flexor spines including the distal pair (vs distinctly longer than carpi, with 3 or 4 movable spines including distal pair in G. sternoornatus );

(6) P2–4 dactyli with 10 movable flexor spines (vs 4–5 spines in G. sternoornatus ).