Sericosura gemmaemonsis, Wang, Jianjia, Lin, Rongcheng, Bamber, Roger N. & Huang, Dingyong, 2013

Wang, Jianjia, Lin, Rongcheng, Bamber, Roger N. & Huang, Dingyong, 2013, Two new species of Sericosura Fry & Hedgpeth, 1969 (Arthropoda: Pycnogonida: Ammotheidae) from a hydrothermal vent on the East Pacific Rise, Zootaxa 3669 (2), pp. 165-171 : 166-168

Sericosura gemmaemonsis sp. nov.

( Fig. 1 )

Material examined. one female, holotype (TVG0901), two females, paratypes (TVG0902, TVG0905), DY115- 21III Station 9, EPR, “Precious Stone Mountain” hydrothermal vent-field, 1.22°N 101.49°W, 1628 m depth, TVG, 2nd November 2009.

Description of the holotype (female): Size large for the genus, leg span 43.1 mm. Trunk ( Fig. 1 A, B) glabrous, dorsal segmentation lines raised, swollen, without dorsomedian tubercles. Lateral processes closelyspaced, separated by 0.25–0.3 times their diameters, with few short distal spines. Cephalon flaring from narrow neck to broad anterior. Ocular tubercle leaning towards anterior, with bifurcate tip, without eyes. Proboscis fusiform, longer than trunk, without constrictions. Abdomen downcurved, extending to midpart of second coxae of fourth pair of legs, with five or six pairs of short dorsal spines.

Chelifores short, scape one-articled, about twice as long as wide, with five or six distal spines, two dorsodistal spines almost as long as scape diameter. Chelae atrophied to knobs, fingers reduced to tiny bumps.

Palps ( Fig. 1 D) seven-articled. First article broad, a truncate cone. Second article longest, slightly longer than fourth, with dorsal and lateral short setae. Third article short with numerous shorter setae and one longer than article diameter. Fourth article with row of erect long setae, three clearly longer than article diameter. Distal three articles very short, seventh longest, of decreasing diameters, with dorsal and distal long setae.

Ovigers ( Fig. 1 C) with few spines and setae. Second article longest, fourth article slightly longer than fifth, and with short lateral setae. Sixth article with short ventral setae. Seventh and eighth articles with dorsal setae longer than article diameters. Seventh, eighth, ninth and tenth with small denticulate spines in formula 2: 2: 1: 2.

Third leg ( Fig. 1 G to H) first coxa with short distal setae. Second coxa distally swollen, longer than first or third coxae, mid-dorsally raised with two longer setae, ventrally with shorter distal setae. Third coxa dorsally with two raised eminences bearing short setae. Femur with row of dorsal and lateral longer setae, and with distal ring of shorter setae, one almost as long as article diameter. Tibiae with dorsal, lateral and ventral setae mostly shorter than article diameters, but some longer than article diameters. Tarsus nearly triangular, with one dorsal spine and 6–8 ventral spines, of length increasing distally. Propodus cylindrical, without heel, with row of short sole spines, 5–6 dorsal and distal setae longer than article diameter. Main claw slender, curved, with two auxiliary claws little more than half main claw length.

Male and juvenile are unknown.

Measurements of holotype in mm: Trunk length from chelifore insertion to tip of 4th lateral processes, 4.61; trunk width across 2nd lateral processes, 2.60; proboscis length, 4.63; abdomen length, 2.44; chelifore length, 0.60; chelifore width, 0.31.

Lengths of palp articles 1 to 7 respectively: 0.35;1.97; 0.43; 1.80;0.32;0.22;0.34.

Lengths of oviger articles 1 to 10 respectively: 0.32; 0.93; 0.49; 0.90; 0.86; 0.48; 0.50; 0.25; 0.32; 0.11.

Third leg, coxa 1, 0.75; coxa 2, 1.72; coxa 3, 1.28; femur, 4.19; tibia 1, 4.23; tibia 2, 4.54; tarsus, 0.28; propodus, 2.16; claw, 0.65; auxiliary claw, 0.48.

Measurements of first leg: coxa 1, 0.69; coxa 2, 1.57; coxa 3, 1.13; femur, 3.94; tibia 1, 4.05; tibia 2, 4.25; tarsus, 0.22; propodus, 1.91; claw, 0.61; auxiliary claw, 0.42.

Etymology. From the Latin gemma mons, meaning Precious Stone Mountain, referring to the new hydrothermal vent field.

Remarks. All the specimens of Sericosura gemmaemonsis sp. nov. collected are females, so we cannot confirm the position of the cement gland tube. However, they are consistent with the genus on other morphological features, such as having the trunk fully-segmented, with transverse ridges, the abdomen articulating, and the cephalon flaring anteriorly; the lateral processes are closely-spaced; the proboscis is large and ovoid; the ocular tubercle has a bifurcate tip; the palps have seven articles, and the ovigers ten articles of which the distal four articles have very small denticulate spines.

Five of the species of Sericosura described previously have seven-articled palps, viz S. venticola , S. cyrtoma , S. hedgpethi Bamber, 2009 , S. heteroscela Child & Segonzac, 1996 and S. mitrata (Gordon, 1944) . S. gemmaemonsis is very similar to the female of the Atlantic species S. heteroscela , although with a much greater leg span. The femur and tibia 2 of S. gemmaemonsis are proportionately more slender and longer, and tibia 2 is the longest article of the leg. In the female of S. heteroscela , the legs are compact, and femur is the longest article. S. gemmaemonsis is also distinct in having two short setae on top of two separate lateral swellings dorsally on the third coxae.

From Bamber (2009) this species would key out to S. cyrtoma , but that species has stouter thorn-like spines on the leg articles and a tapering proboscis, unlike the present species.

There are some differences between the descriptions and the leg of the female ( Fig. 1 E, G) with regard to two longer setae on the mid-dorsally raised of second coxa, as a result of damage to the specimen.

There are some white flocculent material packing on the terminal article of palp ( Fig. 1 D), and few attached on the setae. They are maybe filamentous bacteria.

The specimens from station 21 -S13-TVG9 were taken from the top of a hydrothermal vent, and the television monitor showed smoke issuing from the vent. We could infer from this Sericosura gemmaemonsis may live in the area close to the issuing hydrothermal fluid. Similarly, S. heteroscela were observed in situ one metre from a black smoker (Child & Segonzac, 1996).

The type locality was an active hydrothermal vent.

Figures

FIGURE 1. Sericosura gemmaemonsis sp. nov., TVG 0901, female holotype: A, trunk, dorsal view; B, trunk, lateral view; C, oviger and dentition spine, enlarged; D, palp; E, leg 1; F, tarsus, propodus, and claws of leg 1, enlarged; G, leg 3; H, tarsus, propodus, and claws of leg 3, enlarged. Scale bars = 1.0 mm.