Sericosura dentatus, 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 : 168-170

Sericosura dentatus sp. nov.

( Figs 2–3 )

Material examined: male holotype (TVG0904), one female paratype (TVG0903), 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 (male): Leg span 27.6 mm. Trunk ( Fig. 2 A, B) dorsal segmentation lines raised, swollen, without dorsomedian tubercles. Lateral processes separated by 0.5–1 times their diameters, with few distal short spines. Oviger bases massive, placed just anterior to first lateral processes. Neck with broad anterolateral expansion, elevated dorsally in lateral view. Ocular tubercle a anterior-leaning tube, blind, with bifurcate tip. Proboscis inflated, without constrictions, 0.7 times as long as trunk. Abdomen downcurved, extending to midpart of second coxae of fourth leg pair, with a pair of short dorsal spines and distal short setae.

Chelifores short, scape one-articled, only about twice as long as wide, with distal spines. Chelae atrophied to knobs.

Palps ( Fig. 2 C) nine-articled. First article broad, without spines or setae. Second article longest, with one long dorsal seta and shorter lateral setae. Third article compact, about as long as first article, with long dorsal setae. Fourth article slightly shorter than first article, with more long setae. Distal five articles short, of decreasing diameters and length, with dense long ventral setae.

Ovigers ( Fig. 2 D) first to fifth articles with short setae, fifth article with a long dorsal seta. Sixth article ovoid, with dense long dorsal setae and short ventral spines. Seventh and eighth articles with long dorsal setae. Distal four articles with small denticulate spines in formula 2: 2: 1: 2. Right oviger bearing one egg ball.

Third leg ( Fig. 2 G to I) first coxa with ring of short distal setae. Second coxa longer than first or third coae, with two dorsal setae and cluster of few ventral distal setae. Third coxa distally swollen, densely setose. Femur with dorsal and ventral short setae, and with dense ring of longer distal setae. Cement gland (Fig. 4I) dorsal at centre of femur, basally wide, attenuated. First tibia distally swollen, with dorsal, lateral and ventral setae, and one dorsal seta longer than article diameter. Second tibia slender, with dense dorsal, lateral and ventral long setae, and three dorsal setae longer than article diameter, and with 5–6 ventrodistal spines shorter than article diameter. Tarsus small, subtriangular, with one long dorsal seta, 1–2 short setae and 4–6 longer ventral spines. Propodus without marked heel, with dense sole spines of varied length, and short dorsal setae but with three longer than article diameter, and dense cluster of long dorsodistal setae. Auxiliary claws about 0.6 times as long as main claw.

Measurements of holotype in mm: Trunk length from chelifore insertion to tip 4th lateral processes, 3.26; trunk width across 2nd lateral processes, 2.06; proboscis length, 2.18; egg-ball diameter, 1.32; abdomen length, 1.40; chelifore length, 0.53; chelifore width, 0.22.

Lengths of palp articles 1 to 9 respectively: 0.14; 1.06; 0.16; 0.83; 0.15; 0.14; 0.13; 0.13; 0.07.

Lengths of oviger articles 1 to 10 respectively: 0.40; 0.92; 0.44; 0.94; 0.88; 0.35; 0.12; 0.10; 0.15; 0.06.

Third leg, coxa 1, 0.64; coxa 2, 1.13; coxa 3, 0.71; femur, 2.44; tibia 1, 2.67; tibia 2, 2.44; tarsus, 0.12; propodus, 1.05; main claw, 0.45; auxiliary claw, 0.35.

Measurements of first leg: coxa 1, 0.40; coxa 2, 1.15; coxa 3, 0.55; femur, 2.29; tibia 1, 2.52; tibia 2, 2.31; tarsus, 0.09; propodus, 1.0; min claw, 0.39; auxiliary claw, 0.27.

Distinctions of female ( Fig. 3 ): size slightly larger than male, cement-gland and tube absent, sexuallydimorphic ovigers: ovigers of female almost without setae, and distal four articles with denticulate spines in formula 2: 2: 1: 4.

Etymology. From Latin dentatus , meaning toothed, referring to the species having more finely-denticulate spines on the oviger strigilis than in any other species.

Remarks. There are now five described species of Sericosura with nine-articled palps, including S. verenae (Child, 1987) , S. cochleifovea , S. dissita and S. conta Bamber, 2009 , as well as S. dentatus sp. nov.. The distinct difference between S. dentatus and these other species is the number of denticulate spines on the distal oviger articles. In addition, the proboscis of S. verenae is larger with submedian and subdistal constrictions, and the legs of the female have denser setae. Bamber (2009) has already discussed differences between S. conta and the other three nine-articled species of Sericosura , and those differences also apply to S. dentatus , including more- compact lateral processes, longer auxiliary claws and stouter chelifore scapes. S. dentatus is very similar to S. dissita and S. cochleifovea ignoring the differences in leg spans. Nevertheless, the location of the femoral cement-gland tube in the males is the significant difference between S. dentatus and S. cochleifovea .

From Bamber (2009) this species would key out to Sericosura dissita (of which only the male is known), particularly as the mid-dorsal location of the femoral cement-gland tube in the males of S. dentatus is peculiar in the genus, but similar to that found in S. dissita . A mid-dorsal cement-gland tube is not typical of Sericosura , but the present species increases further the variability of this feature. S. dentatus is distinguished from S. dissita in having denser spination of all leg and oviger articles, no suggestion of secondary articulation of the fourth palp article and a more compact chelifore scape, as well as having denticulate spines on the seventh oviger article (naked in S. dissita ). Sericosura dissita is known only from the type collection, from much further north on the Endeavour Segment of the Juan de Fuca Ridge.

There are some differences between the descriptions and the figures of the male ( Fig. 2 ) with regard to the cement gland on the right first leg and one auxiliary claw, as a result of damage to the specimen.

The body-surface of the specimens is lightly covered with a yellow substance (possibly sulfides), and some white flocculent material is present between the appendages and the trunk ( Fig. 2 A), also between the main claw and the auxiliary claws ( Fig. 3 B), possibly filamentous bacteria.

The sample site was very close to a hydrothermal vent with smoke issuing.

Figures

FIGURE 2. Sericosura dentatus sp. nov., TVG 0904, male holotype: A, trunk, dorsal view; B, trunk, lateral view; C, palp; D, oviger; E, leg 1; F, tarsus, propodus, and claws of leg 1, enlarged; G, leg 3; H, propodus, and claws of leg 3, enlarged; I, cement gland tube of leg 3, enlarged. Scale bars = 1.0 mm.

FIGURE 3. Sericosura dentatus sp. nov., TVG 0903, female paratype: A, leg 3; B, tarsus, propodus, and claws of leg 3, enlarged; C, palp; D, oviger; E, oviger distal articles, enlarged. Scale bars = 1.0 mm.