Sericosura duanqiaoensis, Wang & Huang & Shi & Lin & Niu, 2018

Wang, Jianjia, Huang, Dingyong, Shi, Xiaofeng, Lin, Rongcheng & Niu, Wentao, 2018, First record and a new species of Sericosura Fry & Hedgpeth, 1969 (Arthropoda: Pycnogonida: Ammotheidae) from a hydrothermal vent of Southwestern Indian Ridge, Zootaxa 4420 (1), pp. 131-138 : 132-134

Sericosura duanqiaoensis sp. nov.

( Fig. 1 , 2 )

Material examined. Male (34IV-TVG0802), Station 34IV-SWIR-S035-TVG08, SWIR, 37.66°S 50.47°E, TV- Grab, 1732 m depth, 13 Apr 2015.

Diagnosis. Cephalon extending forward as a hood. Legs of male dimorphic, third and fourth pairs of legs with inflated propodi; first and second pairs of male legs with slender propodi.

Description. Male holotype. Trunk fully segmented, with smooth dorsal ridges, glabrous except for few setae on distal margin of lateral processes, separated by about 0.2–0.3 diameter of lateral processes. Cephalon smooth, triangular, extending forward as a hood. Ocular tubercle low, eyes unpigmented, with few papillae on top. Abdomen long, horizontal, articulated at base, reaching further than distal margin of first coxae, slightly inflated distally, with two rows of setae. Proboscis long, bending down, fusiform, shorter than the trunk.

Chelifore inside the cephalic hood, almost invisible from dorsal view, one-segmented scape, armed with few setae, chela atrophied, globular.

Palp seven-segmented ( Fig. 1-C ; Fig. 2-E, F ), covered by thick sulfide. P1 short, wide; P2 shorter than P4, with few dorsal setae; P4 longest with dorsal and ventral setae, with ventral tube on low proximal protuberance (at 1/3 length); terminal articles armed with short thick setae, P7 longer than P5, P6 shortest.

Oviger 10-segmented ( Fig. 1-F ), O3, O4 and O5 with ectal row of short setae; O6 densely setose; O7 with fewer long setae; O8 with few long setae dorsally; O10 small, less than half length of O9, glabrous; terminal three oviger articles with denticulate spines, formula 2:1:2, spines on O10 very close together.

Legs dimorphic ( Fig. 1-H, I ; Fig. 2-C, D ), posterior four differing from anterior four legs. Major leg articles with ventral, lateral and dorsal rows of setae. Coxa 2 longer than coxa 1 or 3, with ventral and dorsal protuberances on the two posterior pairs of legs. Femora similar in length and spination, cement gland dorsoproximal, small raised bulge opening anteriorly as short, conical tube. First tibiae robust, subequal in length to femur, with two dorsal setae longer than article diameter. Tibiae 2 dimorphic, slender and longest article in anterior four legs, robust, shorter than tibiae 1 in posterior four legs. Tarsus small, subtriangular, with dorsal and ventral setae, ventral setae as long as article diameter. Propodi of posterior four legs clearly inflated, with scattered short lateral setae, long setae dorsally, distal margin armed with cluster of setae and spines dorsally and ventrally; eleven sole spines. Main claw strong, near 0.6 propodal length, sharply curved; auxiliaries slender, about 2/5 main claw length. Propodi of anterior four legs slender, slightly curved cylinder without heel, with dense sole spines of varied length, and dense cluster of dorsodistal setae. Main claw gently curved, half length of propodus; auxiliaries strong, half main claw length.

The female and juvenile unknown.

Measurements of holotype in mm: Trunk length from chelifore insertion to tip of 4th lateral processes, 3.25; trunk width across 2nd lateral processes, 2.23; proboscis length, 2.94; abdomen length, 1.12.

Length of palp articles 1 to 7 respectively: 0.22; 1.25; 0.19; 1.34; 0.21; 0.15; 0.29.

Third leg, coxa 1, 0.67; coxa 2, 1.07; coxa 3, 0.71; femur, 2.45; tibia 1, 2.42; tibia 2, 1.79; tarsus, 0.33; propodus, 2.00; claw, 1.16; auxiliary claw, 0.46.

Measurements of second leg: coxa 1, 0.71; coxa 2, 1.14; coxa 3, 0.72; femur, 2.44; tibia 1, 2.42; tibia 2, 2.48; tarsus, 0.22; propodus, 1.36; claw, 0.69; auxiliary claw, 0.34.

Etymology. From the Chinese “Duan Qiao”, meaning Broken Bridge, referring to the hydrothermal vent field from which the new species was collected.

Remarks. The most striking features of the new species were the posterior pairs of legs with expanded propodi; only Sericosura heteroscela Child & Segonzac 1996 from the Mid-Atlantic Ridge and Sericosura dimorpha Arango & Linse 2015 from the Scotia Ridge were hitherto known to have similar characters. Arango and Linse (2015) had discussed the differences between the species with dimorphic propodi. The evident differences found in S. dimorpha compared to the new species are the undiscovered femoral cement gland, simple oviger spines, longer main claw and ridged trunk. Based on Bamber's key for the genus ( Bamber, 2009), the new species resembles S. heteroscela which has a taller ocular tubercle, no extended cephalon, fine denticulate spines of oviger and fewer setae on coxa 2.

Figures

FIGURE 1. Sericosura duanqiaoensis sp. n., 34IV-TVG0802, male holotype: A, trunk, dorsal view; B, trunk, lateral view; C, palp; D, tubercle on the fourth article of palp, inner view, enlarged; E, terminal articles of palp, enlarged; F, oviger; G, terminal articles of oviger, enlarged; H, leg 3; I, leg 2; J, tarsus, propodus and claws of leg 3, enlarged; K, tarsus, propodus and claws of leg 2, enlarged; L, cement gland tube of leg 3, enlarged. Scale bars A, B, H, I = 1.0 mm; C, F, J, K = 0.5 mm; E, G = 0.2 mm.

FIGURE 2. Sericosura duanqiaoensis sp. n., 34IV-TVG0802, male holotype: A, trunk, dorsal view; B, trunk, ventral view; C, leg 2; D, leg 3; E, F, palp, lateral view, arrow indicating the protuberance and tubercle.